2.4 wants to stall when accelerating from complete stop
 

Hello all. A few days ago my 2.4 supercharged Alero was barely able to stay running. Got the plastic ignition cover replaced (white plastic housing which holds coils), now it idles perfectly. Unfortunately, it seems there may have been a second problem hiding underneath the first.

When I left the dealership, it ran like it should. No hesitation, heavy throttle from stops were not a problem. Three miles down the road, I came to a complete stop and tried to accelerate. The car started choking out, almost stalling completely. I got it home the next twenty miles, but at each stop it did the same thing.

Today I took it for a test drive. The car started normally, I could apply a good amount of throttle from a stop without problems in my driveway. I drove a mile down the road, came to a stop, tried to go and it started choking again. It was the same at each stop after.

So the problem is it seems to be choking out after stopping and trying to accelerate, but only once it heats up or has been driven a mile or two. The engine does not surge or do anything strange while idling.. In fact it sits almost perfectly at 800 RPMs during idle, no misses at all, no codes thrown. But once the throttle is down, it chokes for a second or three then surges to life and goes. It has never died totally where I had to restart the engine, but it seems very close to doing so.

I have found if i give it *barely* any throttle, it seems to not choke. On the other hand, the more I give it from a stop, the worse it acts. So basically more gas = more choking.

I drive 40 minutes every morning to work and I'm doubting its reliability at this point. I don't want to cause a 3-lane rush hour traffic pileup like I did two weeks ago so I could push it to the shoulder, lol. I am thinking it could be a number of things: fuel filter, fuel pump, air intake issue, bad sensor, bad ECU, bad load of gas.

Any ideas? As always, any advice is greatly appreciated!

Can you give a little more background, like how long has the supercharger been on the car, and how was it running before 2 weeks ago when you said it died in traffic. You took it to the dealership right after that happened? I'm trying to see if it slowly got worse over time or failed quickly.

Sure, thanks for the reply! The supercharger has been in it for four years. I installed it when there were 70,000 miles on the car, it now has 129,000. The profile for the S/C kit was flashed into the ECU by a GM dealership immediately after it was installed, so the S/C has been functional for quite some time.

Four months ago I replaced the engine with a brand new Goodwrench engine purchased through the dealership. I installed this myself and had it inspected. I followed the break-in procedure exactly. It ran perfectly up until now.

The plastic coil housing has been replaced three times over an 8 year period. It seems like that part is not designed very well.

The catalytic converter in my car plugged at one point, and so the guts were punched out of it. The sensors have never complained and no codes have been thrown because of this. I would have replaced it a long time ago but 7 years of college leaves you broke even after you graduate.

I recently replaced the starter because the old one died. I replaced the belt tensioner at the same time because I had easy access to it with the S/C off. The belt was also replaced with the correct Gatorback version for the S/C kit.

When my car died in traffic, I was doing 65 MPH and suddenly there was no power. Pressing the throttle down did nothing. There were no exits to get off the highway and no shoulder, so I coasted as far as I could until the engine died and it came to a stop. I then got out and pushed the thing up the highway to a shoulder with the car in neutral. This problem, which completely disabled the car (the white plastic coil housing), was instantaneous and had no prior indication anything was failing.

When I first brought my car in, my regular mechanic said he thought the timing chain may have jumped a tooth because it was running so rough. It would not even go into gear, it would die. Because the engine I bought has a 3 year, 100k warranty I towed it from there to the dealership which is where it was fixed 3 days ago. They checked the chain and said the marks lined up. The problem was apparently the coil housing I mentioned earlier, which was replaced. This drastically improved things. It will at least run now, but with this little problem I have stated.

I haven't noticed anything that would lead me to think something degraded and then died. It has never had problems accelerating from a stop. It seems like this new problem might be related to engine RPMs. The car accelerates fine as long as you are already at speed. It is when it drops down to near-idle RPMs that it can be choked by applying any more than the tiniest bit of throttle.

If you have any more questions, let me know.

I've had similar problems with my S/C setup also. 1st time found the vaccum/boost sensor had popped out, easy find and fix. 2nd time it ended up being a failing TPS sensor. There is a re-calibrate procedure, which worked for a while but I ended up replacing it via Autozone. Simple swap-out was worth it, the shaft had cracked in the original one. When the ECU can't read the throttle position properly it lets the vaccum signal tell it what it needs to do about the fuel injection which is inaccurate and laggy. Good luck!

This is a very good recommendation, I will pick up a new TPS tomorrow and install it. For $40 it is definitely worth a try. If I am swapping a new one in, does it need calibration?

Also what is the vacuum/boost sensor? Is this a MAP sensor?

I've had a couple TPSs fail also, and vacuum-related problems as well. I can relate to the problem you're having, got a minor version of it right now in fact. But mine is a V6, though. I believe MMGT1 recommended a crank position sensor replacement on mine, but I haven't found time to do that yet.

What happens if you power brake it to about 1200 rpm, and then floor it? Does it still hesitate/stall out then?

Bypass actuator working OK?

Installed a new TPS today, did not fix the problem. =(

It doesn't matter if I have the brake on or not, the engine will hesitate. It does it in park, drive and neutral also.

I checked the S/C bypass valve system. The actuator/solenoid is working fine. It's not closing the bypass too early, only under a good amount of throttle. I don't think it's choking from too much air through the S/C early on.

I messed with it some more today. As I said before, it idles fine but hesitates between 900 and 1300 RPMs. Once it is below or above this range, everything works normally without any hesitation.

I suppose I will need to have someone use a scanner to see what's going on during these hesitations. Seems to me it might be a problem with air or fuel. Maybe the ECU is going crazy.

With a supercharged setup, you would definitely benefit from a MSD Ignition Coil swap and some NGK spark plugs.

Yes I hear the MSD coil swap is the way to go! After I know how much this problem is going to cost me, I will look into it.

Why do you say NGK spark plugs? I'm using the plugs specified in the S/C manual, are the ones you mentioned better?

Whats your AFR looking like cause it sounds like you could be running real rich you already said your cat was clogged and you had to punch it out.

I'm not sure what the ratio is, going to get it checked early this week.