intermittent "rough" start

alero_bmxer · 12-20-2010, 11:19 AM

for the past few months my car sometimes starts and stumbles a little. doesn't happen every time i start it, it just randomly happens. sometimes twice a day sometimes none. it never stalls, just kind of has almost a misfire for the first few seconds of it running, after that its totally normal. 2 months ago it got plugs and wires when i did the Accel coils, but this was happening before the coils so i don't see those being the culprates. i was thinking fuel pressure regulator or IAC valve. could be wrong so thats why i'm asking. on a side not there is no SES light thrown during these happenings.

[ion] C2 · 12-20-2010, 12:01 PM

normal, happens here too

alero_bmxer · 12-20-2010, 12:07 PM

cold weather was a thought also but i don't remember it happening last year. o well as long as its normal I'm not worried.

Chris2000 · 12-20-2010, 12:15 PM

Just for peace of mind I always suggest the iac valve being replaced since my car had issues related to yours, it turned out to be duralasts' garbage refurbished parts and the iac valve kept getting stuck open. Finally switched it to acdelco and car runs amazing. If you have some extra cash might as well just change it see if it does change something, the iac valves at least where i'm from almost always have a 1 year or longer warranty so it can't hurt.

Philbar71 · 12-20-2010, 02:37 PM

My car stumbles and stalls out a bit too in cold weather if I dont let it sit and warm up before driving.

alero_bmxer · 12-20-2010, 03:10 PM

Quote:

Originally Posted by Chris2000

Just for peace of mind I always suggest the iac valve being replaced since my car had issues related to yours, it turned out to be duralasts' garbage refurbished parts and the iac valve kept getting stuck open. Finally switched it to acdelco and car runs amazing. If you have some extra cash might as well just change it see if it does change something, the iac valves at least where i'm from almost always have a 1 year or longer warranty so it can't hurt.

ya i priced one out a while ago at work and it was only like 40 bucks so i might change that. on occasion it will also have a funny idle drop after driving to/from work on the expressway. like when i get off the expressway, and get stopped at a light, when i come to a complete stop the rpm's will drop about 100-200 and then right back to normal a couple times.

Quote:

Originally Posted by Philbar71

My car stumbles and stalls out a bit too in cold weather if I dont let it sit and warm up before driving.

mine has never stalled it just runs rough for a few seconds after first starting. if i give it some gas, in the 2-3k range, it immediately goes away.

Chris2000 · 12-20-2010, 06:12 PM

Yeah i'd suggest changing the iac. What you can do is when you're at work before you go in to start (come like 30 mins early) take the iac valve out its only 2 bolts. I'm drawing a blank right now and can't remember the size but its 2 torx bolts. Only takes less than 10 mins to take it out and put a new one in. What you could do is take it out and check it. If it's stuck open you'll be able to tell. When we took mine out we poked it (seriously) and the tip fell off and the spring flew off

. Just don't buy a duralast one, i've learned my lesson already.

But yeah if you let off of the gas and you see the rpms drop significantly and it seems/sounds/feels like its relieving pressure then definitely.

[ion] C2 · 12-20-2010, 11:49 PM

I changed the IACV and that doesn't change anything. I monitored the IACV position versus the commanded position and both react instantaneously. I doubt it's an IACV issue.

All of the IAC valves' pintles fall off and the spring shoots out if you mess with them. It's not a faulty part. Don't blame "Duralast" for everything. Wells makes AutoZone's electrical components, and they are a decent name in automotive electronics. Just because you're messing around with a sensitive part that every automotive site will say "DON'T force or touch/move the pintle by hand" and it shoots off doesn't make the part bad; it's your fault.

If it's stuck open while the car is running you won't be able to tell by looking at it. You need to monitor the IAC counts/position with a datalogger.

Philbar71 · 12-21-2010, 02:58 PM

^ Yep if its stuck and wont move while the car is on then when you put a stress on the engine (like AC, Defrost, Headlights) then you will be able to notice the drop in idle RPMs. Also as your driving around and you take your foot off the throttle then the engine will almost immediately drop to idle RPMs - Also when this happens my Traction Control goes off... Anybody got an idea?

Mine likes to get stuck in really cold weather sometimes and it's extremely annoying because it idles constantly at about 850-900 RPMs even when the engine is warmed up fully.

And my car has stalled out only once, it was on a cold morning where the temp was like 10F outside and I didnt let it warm up but for like a minuet. lol.

2fastshifter · 12-21-2010, 05:08 PM

Wel i got some rotten idling last week.
Engine kept running in idle but far from smooth.
Pulled my iac, it was black with a lot of carbon buildup, really much.
Cleaned the thingy with a dry cloth, cleaned the hole where it was,
Checked sparkplugs and for vacuumleaks,
Resetted PCM,
Now she's running just fine with really very cold weather.
More and more i am enjoying DIY!
Respect to this forum peeps!

12-24-2010, 12:16 PM

Cold weather rough idle is a known TSB, I think the dealership has an update for the computer.