Car Won't stay running after engine swap

[crankycowboy]

Hey guys. I have had an interesting journey with this. If you want the history...see here: http://www.aleromod.com/forums/showthread.php?t=35829

In summary, my daughter blew her head gasket (2003 3.4 alero). The heads were warped too bad so I opted to pull a 1999 engine from a junk yard and throw it in there using several of the 2003 components. That engine had a slightly blown head gasket as well. I changed that out, had the heads surface ground etc. and I got two of the push rods swapped and bent a valve. Pulled it all apart again, had the valve work done, new gaskets, and now finally it runs smooth, no overheating...everything is back to normal....ALMOST.

I let the car idle in the driveway for about 20 min to let it get to temp etc before driving it. I then drove it through the neighborhood and everything seems fine. Only problem I'm having is the car won't idle. If I completely remove my foot from the gas it may sputtter a little, and then die. I have verified that the IAC is moving in and out when the ignition is started. I made sure the throttle body is nice and clean and there is no buildup in the IAC. Some people have suggested that since the car sat for so long without a battery (and that I changed several components), that the car needs to be driven more so that the computer can re-learn all the parameters. Does this sound feasible or does it sound like something else? Any help would be greatly appreciated as I am SICK of this project. Thanks!

[zearchyo]

couldnt it be fuel related, like fuel pump going bad

[jabartram]

have you tested fuel pressure? try a new fuel pressure regulator. unplug the MAF sensor to see if it will idle, but be prepared the tranny will shift very very hard from neutral to drive and to reverse.

[Starglow]

The computer will not cause a stall condition. Check the fuel pressure readings at idle and also check for vacuum leaks. How old is the gas in the fuel tank? Try some fresh fuel to see if that helps.

[jabartram]

The computer will not cause a stall condition. Check the fuel pressure readings at idle and also check for vacuum leaks. How old is the gas in the fuel tank? Try some fresh fuel to see if that helps.

mine does, it hunts at idle sometimes because im still working on my fuel trims, so yes a PCM will cause stall conditions, but it is less likely in this scenario, but a MAF sensor going bad can cause the same issue.

[crankycowboy]

Thanks for the replies guys. If it was a MAF sensor wouldn't I be getting some sort of code like a P0101-P0103? Or a Lean/rich or fuel trim type code indicating a fuel problem?

And the reason I inquired about the computer was because on my Dodge Ram, it did the exact same thing until I drove it for about 40 miles. I researched on the net, and it's a pretty common problem when battery has been disconnected for quite some time...but didn't know if any of you guys had experienced somethign similar with these cars.

[crankycowboy]

couldnt it be fuel related, like fuel pump going bad

Fuel pump was replaced about 6 months ago. And once again, it's not showing any signs or rough idle or anything other than it just won't stay running if you take your foot off the gas. And didn't have any issue prior to doing the engine swap. I probably should have also mentioned that when I drove it, I can give it gas and it revs and accelerates fine, no bogging or other issues, aside from idle.

[xXManwhoreXx]

Does your pcm still think your running the old motor? 99 motors had some slight diffrences

[crankycowboy]

Does your pcm still think your running the old motor? 99 motors had some slight diffrences

Good point. I haven't done anything to the PCM, which is why I thought my question regarding "re-learning" was valid. I used most of the components from the 2003 motor (fuel rail, injectors, cps, all the sensors etc....so I think I should be good?

[jabartram]

check the fuel pressure.

[xXManwhoreXx]

Fuel pressure should be fine... What about the throttle body is it closing at idle to far and choking itself out???

[Redog]

I didn't think 99's had EGR? but that wouldn't cause the issue your having.

I agree with Eric and wonder if the TB is closing too much. Never heard of it on a FI car, but it could be possible. What about the fuel filter? A faulty fuel pump on these cars is never in the "going" stage. It has two different operating moods. Working or Not working.

Check to see if the coil packs are tight. Plug wires aren't loose on the plugs. No burn connections bewteen the ICM and wireing hardness

[a.graham52]

if you drove it for 10 miles thne you probably let the computer relearn what ever it needs to to make adjustments. have you driven it since? as far as any of the sensor going bad and not throwing a light: if the sensors still within "spec" but is no where near the useable area (such as maf sensor thinking there is a shit-ton of air going in when realy your idleing) thne it can cause weird things and no lights.

[03glgold]

i will say that when i had to replace my fuel pump a couple months ago, i went to a friends and the store and back to my dorm and everything was fine...i went out 5 minutes later to go check on something and it had a slight stall at idle, drove it about 3 miles in the country and as soon as i let it drop to idle it was gone...the code came on about 30 seconds before it got to the point of refusal to start.

[comanche]

Car most likely needs a crank relearn, performed with a Tech 2 at your local friendly money-loving dealership.

I've done 10-15 GM engine swaps with no mishap, about 5 were 3400s, but I did have one that ran fine for 5 minutes, then bogging down. Only fixed was a crank relearn. (First the dealership sold me a MAF, but I made them take it back when it didn't fix the problem -I was selling the car anyways)

[[ion] C2]

unplug o2 sensor(s) (upstreams)

see if problem goes away

[crankycowboy]

Fuel pressure should be fine... What about the throttle body is it closing at idle to far and choking itself out???

It sort of seems like this could be what's happening, but how do I check that?

[crankycowboy]

if you drove it for 10 miles thne you probably let the computer relearn what ever it needs to to make adjustments. have you driven it since? as far as any of the sensor going bad and not throwing a light: if the sensors still within "spec" but is no where near the useable area (such as maf sensor thinking there is a shit-ton of air going in when realy your idleing) thne it can cause weird things and no lights.

I have driven it, but probably only about a mile or so through the neighborhood. Maybe just to mark that out of the equation, I should take it for a "spin"

[crankycowboy]

C2;617512']unplug o2 sensor(s) (upstreams)

see if problem goes away

I will give this a go and report back. Thanks.

[crankycowboy]

Car most likely needs a crank relearn, performed with a Tech 2 at your local friendly money-loving dealership.

I've done 10-15 GM engine swaps with no mishap, about 5 were 3400s, but I did have one that ran fine for 5 minutes, then bogging down. Only fixed was a crank relearn. (First the dealership sold me a MAF, but I made them take it back when it didn't fix the problem -I was selling the car anyways)

Thanks, I will exhaust all the other suggestions made here first before going the "dealership" route, ouch!

Speaking of MAF sensor....When I was pulling the air intake "box lid" off I lifted too much and broke one of the tabs that holds it down. Could it be "sucking" air without going through the filter first and causing additional problems, or is that a stretch (I'm sure you can tell I'm grasping at straws at this point).

[[ion] C2]

I will give this a go and report back. Thanks.

In case you're curious, the reason behind my suggestion:

O2 sensor might suck and is maxing rich occasionally, causing car to pull all fuel til it corrects it. Mine currently is failing and sometimes does this making my car die, lol, even though the tune is perfect and it runs smooth in open loop (no O2 sensor input). My air/fuel ratio bounces around too much lately with the O2 sensor active; it overshoots a lot and is generally annoying due to it maxing rich/lean a lot because it's not moving fast/accurately enough to maintain a proper control on the ratio.

[a.graham52]

Thanks, I will exhaust all the other suggestions made here first before going the "dealership" route, ouch!

Speaking of MAF sensor....When I was pulling the air intake "box lid" off I lifted too much and broke one of the tabs that holds it down. Could it be "sucking" air without going through the filter first and causing additional problems, or is that a stretch (I'm sure you can tell I'm grasping at straws at this point).

no, air would still be getting metered through the maf sensor. if air was leaking after the sensor such as the intake gasets etc... then yo uwould have a problem.

[crankycowboy]

C2;617523']In case you're curious, the reason behind my suggestion:

O2 sensor might suck and is maxing rich occasionally, causing car to pull all fuel til it corrects it. Mine currently is failing and sometimes does this making my car die, lol, even though the tune is perfect and it runs smooth in open loop (no O2 sensor input). My air/fuel ratio bounces around too much lately with the O2 sensor active; it overshoots a lot and is generally annoying due to it maxing rich/lean a lot because it's not moving fast/accurately enough to maintain a proper control on the ratio.

Thanks for the input. Yeah, the 1999 engine came with a o2 sensor on it, but I had bought the one on there just about 6 months ago, so opted to put that one back on; however, I have heard that occasionally in engine swaps etc...rtv/silicone can cause o2 sensors to go downhill so I'm not ruling anything out at this point. My biggest problem is twisting someones arm to come over as I have to keep my foot on the gas anytime I try to do something while running otherwise it obviously dies. But in this case, I'll unplug and see what happens. I did the same thing to the MAF and it didn't effect idle, just ran worse....lol

[a.graham52]

does it run nice and smooth when you hold the throtle at "idle speed"? could be the IAC valve acting up even though you said it cycles.

[crankycowboy]

does it run nice and smooth when you hold the throtle at "idle speed"? could be the IAC valve acting up even though you said it cycles.

It does run nice and smooth as long as I keep my foot on the gas. It also revs fine and accelerates great when driving. It's really just the idle that's the problem. When I take my foot off the gas it dies immediately (usually), but I have noticed if I let it run for a long period in the driveway, it will sort of "sputter" before dying....so maybe driving it would help. In regard to the IAC valve...that would be my first guess...but I actually had another one from the engine I bought (i used the intake off the previous engine), and I tried it....with same results.

[AleroB888]

Good point. I haven't done anything to the PCM, which is why I thought my question regarding "re-learning" was valid. I used most of the components from the 2003 motor (fuel rail, injectors, cps, all the sensors etc....so I think I should be good?

As long as you're reaching, you could try switching both '99 cps's back.

[crankycowboy]

As long as you're reaching, you could try switching both '99 cps's back.

Well as mentioned a couple of posts back, there are just a few differences between the 2003 and the 1999. The CPS was one of them. The connector that plugs into the wiring harness is different so I couldn't connect it and I couldn't splice in the connector because the 2003 the connected is directly on the sensor opposed to having leads coming off (meaning there are no wires).

[crankycowboy]

Ok, well I got home and took the car for a drive on the highway. I drove about 13 miles. When I got back and pulled into the driveway, the car died the minute I took my foot off the gas :( I tried disconnecting the o2 sensor as was suggested which didn't have any noticible difference. I did notice however, if I don't just take my foot off the gas and sort of ease the rpms down....that it will stay running (roughly), where rpms will drop down to around 500 or less and then bump up (where it's obviously trying to keep itself running), it will bump up and down like that for about 60 seconds until finally it will lose it and die. I'm sort of running out of things to try. Any other ideas short of taking it to the dealer as was suggested? Does it need to be driven further for the computer to relearn? I put my code reader on there and it's saying all systems aren't ready yet....so do I need to drive it until everything is in "ready" status?

[[ion] C2]

probably vacuum leak then

there's no "relearn" that can fix this shit. this is a mechanical/electrical problem, not PCM

[AleroB888]

You could try introducing a small air bypass around the throttle body, route a hose with a flow restrictor to loop around it, see if it maintains an idle. May be a VE difference between the 2 engines at idle.

[crankycowboy]

C2;617555']probably vacuum leak then

there's no "relearn" that can fix this shit. this is a mechanical/electrical problem, not PCM

Believe me, I'm not a COMPLETE idiot, and this stupid thing has me scratching my head. There are only a couple places that require vacuum that effect the idle, right? Where do you suggest I check?

[crankycowboy]

You could try introducing a small air bypass around the throttle body, route a hose with a flow restrictor to loop around it, see if it maintains an idle. May be a VE difference between the 2 engines at idle.

I'm sorry AleroB888, I'm up for trying anything...I'm just not completely sure what you are suggesting, can you please elaborate?

[AleroB888]

I'm sorry AleroB888, I'm up for trying anything...I'm just not completely sure what you are suggesting, can you please elaborate?

There is a certain amount of air leakage past the throttle plate. Some throttle plates also have a small hole drilled in them to fine tune that amount. Rather than add or enlarge a hole in the throttle plate, you could try looping a vacuum hose around the throttle body.

I know the IAC is supposed to compensate for that, but I have run into situations in modded setups especially, where it still needed more air.

The PCM should command 20 degrees of timing with the TPS at zero percent, throttle plate closed. What parameters are you able to read on your scanner?

What I am suggesting is something just to get it drivable untill you can research it more. Engine/PCM interactions can be frustrating.

[a.graham52]

call a local dealer and ask how much to do the crank relearn proceadure.

[crankycowboy]

Ok guys, I have a question...I may be on to something. Can the throttle cable "stretch"? I noticed some "play" in the cable at idle, and we kept saying it was sounding like maybe the "butterfly" was closed too much and choking it out. So I took a piece of vacuum hose and sliced it down the center and put it over the accelerator cable (so that there was more tension from the get-go). And wala.....the car starts without me having to put my foot on the gas and idles beautifully (just under 1k), smooth and quiet. Now, obviously this is a "band-aid", but could it be the throttle cable? What else could be the "real" problem? Please see attached picture for the temp solution.

[AleroB888]

Ok guys, I have a question...I may be on to something. Can the throttle cable "stretch"? I noticed some "play" in the cable at idle, and we kept saying it was sounding like maybe the "butterfly" was closed too much and choking it out. So I took a piece of vacuum hose and sliced it down the center and put it over the accelerator cable (so that there was more tension from the get-go). And wala.....the car starts without me having to put my foot on the gas and idles beautifully (just under 1k), smooth and quiet. Now, obviously this is a "band-aid", but could it be the throttle cable? What else could be the "real" problem? Please see attached picture for the temp solution.

If it is, that would be the throttle plate clearance I mentioned. It has an adjustable stop, but you can not open it up so far that the TPS reads more than zero degrees when closed. Hence also why some plates have a hole drilled.

Also, the throttle cable does not hold the plate open at idle, it should have a tiny bit of slack.

[xXManwhoreXx]

So I was right! Muahaha..

There should be some kind of screw to tighten the cable but idk ive never messed with the tb on my ho

[a.graham52]

Also, the throttle cable does not hold the plate open at idle, it should have a tiny bit of slack.

x2 therefore i think what your doing is just holding the throttle plate open compinsating for the real issue.

[crankycowboy]

If it is, that would be the throttle plate clearance I mentioned. It has an adjustable stop, but you can not open it up so far that the TPS reads more than zero degrees when closed. Hence also why some plates have a hole drilled.

Also, the throttle cable does not hold the plate open at idle, it should have a tiny bit of slack.

AleroB888, I said a few posts back that I wasn't a COMPLETE idiot...I may have to retract that statement. I guess through all the times that I have had this thing on and off that I never noticed there was a physical stop (I assumed the length of the cable controlled the stop and the IAC controlled the rest). I had an extra throttle body, so I looked at it and now I feel really stupid (see attached pic, just in case it helps someone else). I did notice that there is a lot of "play" where the cable mounts to the "bracket". I can grab the cable and move it in and out and either rev it or kill it just by the amount of play there is where it secures to the bracket....so maybe with me pulling it off and on a 100 times, caused this? How do you suggest I adjust things as it appears that I can't access it while on the car, or can I? Thanks a lot guys for sticking with me through this mess and sorry to have to point out how dumb I apparently am.

[AleroB888]

AleroB888, I said a few posts back that I wasn't a COMPLETE idiot...I may have to retract that statement. I guess through all the times that I have had this thing on and off that I never noticed there was a physical stop (I assumed the length of the cable controlled the stop and the IAC controlled the rest). I had an extra throttle body, so I looked at it and now I feel really stupid (see attached pic, just in case it helps someone else). I did notice that there is a lot of "play" where the cable mounts to the "bracket". I can grab the cable and move it in and out and either rev it or kill it just by the amount of play there is where it secures to the bracket....so maybe with me pulling it off and on a 100 times, caused this? How do you suggest I adjust things as it appears that I can't access it while on the car, or can I? Thanks a lot guys for sticking with me through this mess and sorry to have to point out how dumb I apparently am.

Did you use the original throttle body, upper intake, and same type gasket? If not, it is possible the flange opening for the IAC got accidently obstructed.

You may have a couple turns of adjustment possible on the screw before it goes out of spec (more than zero degrees). There is also a TPS relearn, iirc., but not usually needed.

Compare the two throttle body blades (does either or both have a hole drilled?), and are the mounting flanges the same?

The return spring on the throttle body is stronger and overrides the gas pedal return spring. The car should idle even with the cable off.

I don't think it's anything you caused, but looks difficult to adjust in the stock location. Can you get a flat feeler gauge to prop open the set screw slightly, while checking the TPS readout?

[crankycowboy]

Did you use the original throttle body, upper intake, and same type gasket? If not, it is possible the flange opening for the IAC got accidently obstructed.

You may have a couple turns of adjustment possible on the screw before it goes out of spec (more than zero degrees). There is also a TPS relearn, iirc., but not usually needed.

Compare the two throttle body blades (does either or both have a hole drilled?), and are the mounting flanges the same?

The return spring on the throttle body is stronger and overrides the gas pedal return spring. The car should idle even with the cable off.

I don't think it's anything you caused, but looks difficult to adjust in the stock location. Can you get a flat feeler gauge to prop open the set screw slightly, while checking the TPS readout?

I did use the original upper intake; however, I believe the throttle body was "gummed" up more on the original so I compared the two and didn't notice any differences and swapped them and cleaned up the latter...but I could be wrong. I happen to have the one not on the car with me, and it does have a hole in the blade, but I will have to wait until I'm home to check the other. Like I said, the IAC valve moves in and out when I turn on/off the ignition, so shouldn't that take care of all of this as long as it's not sticking and it's working properly? I feel a lot better, and I'm obviously getting closer....but still a few "hiccups" especially if it SHOULD be able to run without the cable. I will certainly have to compare the throttle bodies as you suggest. The gaskets were indeed the same, and a new one came with the complete gasket kit I purchased.

[a.graham52]

I did use the original upper intake; however, I believe the throttle body was "gummed" up more on the original so I compared the two and didn't notice any differences and swapped them and cleaned up the latter...but I could be wrong. I happen to have the one not on the car with me, and it does have a hole in the blade, but I will have to wait until I'm home to check the other. Like I said, the IAC valve moves in and out when I turn on/off the ignition, so shouldn't that take care of all of this as long as it's not sticking and it's working properly? I feel a lot better, and I'm obviously getting closer....but still a few "hiccups" especially if it SHOULD be able to run without the cable. I will certainly have to compare the throttle bodies as you suggest. The gaskets were indeed the same, and a new one came with the complete gasket kit I purchased.

imo i dont like the idea of messing with that adjustment... just doesnt feel right to me. i would think your IAC would be able to compinsate for it. that stop is probably only there to stop the blad from jamming into the TB and locking up.

[crankycowboy]

Did you use the original throttle body, upper intake, and same type gasket? If not, it is possible the flange opening for the IAC got accidently obstructed.

You may have a couple turns of adjustment possible on the screw before it goes out of spec (more than zero degrees). There is also a TPS relearn, iirc., but not usually needed.

Compare the two throttle body blades (does either or both have a hole drilled?), and are the mounting flanges the same?

The return spring on the throttle body is stronger and overrides the gas pedal return spring. The car should idle even with the cable off.

I don't think it's anything you caused, but looks difficult to adjust in the stock location. Can you get a flat feeler gauge to prop open the set screw slightly, while checking the TPS readout?

AleroB888, well this just gets more and more fun. I got home and was able to check. The two throttle bodies are indeed different. I didn't remove the one currently on the car, but I pulled the breather box boot away and the throttle plate on the car is a solid plate while the one I have (which I believe is the one previously on the car) has a hole drilled through it as you mentioned some do. Could these slight differences be the cause of my issue? Yes, I know...there is one way to find out, but was looking for input.

[crankycowboy]

imo i dont like the idea of messing with that adjustment... just doesnt feel right to me. i would think your IAC would be able to compinsate for it. that stop is probably only there to stop the blad from jamming into the TB and locking up.

I agree, adjusting that stop is just compensating for the real problem....which I haven't nailed down yet. I did swing by a junk yard and picked up another IAC just for grins, with the same result. And I did verify once again that it is at least moving when turning ignition on and off.

[AleroB888]

AleroB888, well this just gets more and more fun. I got home and was able to check. The two throttle bodies are indeed different. I didn't remove the one currently on the car, but I pulled the breather box boot away and the throttle plate on the car is a solid plate while the one I have (which I believe is the one previously on the car) has a hole drilled through it as you mentioned some do. Could these slight differences be the cause of my issue? Yes, I know...there is one way to find out, but was looking for input.

That hole in the plate will affect it, also check the throttle body flange at the IAC opening, some TB versions have no cutout for it on the flange.

You can just swap the plates with it on the car iirc, but I would take the whole unit off and inspect it.

[a.graham52]

That hole in the plate will affect it, also check the throttle body flange at the IAC opening, some TB versions have no cutout for it on the flange.

You can just swap the plates with it on the car iirc, but I would take the whole unit off and inspect it.

why couldnt you just swap out whole throttle bodys?

[AleroB888]

why couldnt you just swap out whole throttle bodys?

If the mounting flanges or IAC passage are different, he should definitely swap the original TB back in. But it might be of interest just to see if the plate fixes it. Then again, it can be tricky messing with the plate, so he's probably better off swapping the whole thing.

[AleroB888]

So what happened to this thing already? :)

[crankycowboy]

So what happened to this thing already? :)

Sorry, I went out of town for the extended weekend. Well I did as you guys suggested and switched to the other throttle body, and I'm happy to say that everything works perfectly now. I'm truly amazed it made that much of a difference. I put them side by side, and literally the only difference I could find was the hole in the plate. See attached picture. I was able to remove the piece of rubber hose that was keeping the butterfly open and all is back to normal. In any case, I really appreciate you guys sticking it out with me and offering all the solutions throughout this rather painful process.

[xXManwhoreXx]

Clear her corners!

I had too....

I'm glad everythings good now!

[zearchyo]

glad to hear u got everything solved