rough idle at start up cold
Le Mans Master
Joined: Aug 2004
Posts: 5,141
Likes: 7
From: Metairie Louisiana
I'm having the exact same problem. (See threads below) Someone's gotta know. No codes shown. Keep me up to date if you figure it out. This weekend I'm going to start by changing the fuel filter and fuel injectors. (Something I wanted to do anyway)
http://forums.corvetteforum.com/show....php?t=1343675
http://forums.corvetteforum.com/show....php?t=1351435
Thanks
http://forums.corvetteforum.com/show....php?t=1343675
http://forums.corvetteforum.com/show....php?t=1351435
Thanks
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
I have been cleaning, fixing a re-setting those idle speed control motors for the last 20 years on all kinds of cars we have owned. Yes I have had some success, and other times done the job again many times over. 
That was then, now I don't mess around with them anymore except to troubleshoot the problem. I just change them out now because their so tempormental and I just want to get the problem fixed and be done with it. And yes I know there expensive, 
but easy to change and at least you know where the problem is not. But it's usually money well spent and generally takes care of the problem.
Hope I have not stuck my foot in my mouth to far, good luck!
That was then, now I don't mess around with them anymore except to troubleshoot the problem. I just change them out now because their so tempormental and I just want to get the problem fixed and be done with it. And yes I know there expensive, but easy to change and at least you know where the problem is not. But it's usually money well spent and generally takes care of the problem. Hope I have not stuck my foot in my mouth to far, good luck!
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Originally Posted by ittlfly
When was the last time you cleaned the TB and the IAC? I'd start there and then reset the IAC according to the FSM.
Just did this to my TB and the car starts quicker now! No codes, this would be a good place to start.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
When the engine is cold, the ECM doesn't correct fuel delivery for minor vacuum leaks, plugged up injectors or sensors that are working but reporting the wrong info. Scanning it in closed loop (warmed up) will tell you what corrections are being made - more fuel or less - and lead to a better diagnosis. Before you start, verify that the Coolant Temp and Manifold Air Temp Sensors read the same and are close to the outside air temp.
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Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Another thing to try. Disconnect the battery terminal, leave off for a minute and reconnect. This will reset the PCM and it will have to re-learn the idle speed. This will probably not work but you never know when a BIT might be hung up in the PCM computer. 
Just another thought.
Just another thought.
Team Owner
Joined: Oct 2000
Posts: 96,443
Likes: 9
From: Fort Knox, KY
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It could also be the EGR valve.
If the engine's getting too much EGR flow at idle, cruise, or cold operation, the engine could stall after start, the engine could stop at idle after deceleration, the car could surge during cruise, or the engine could exhibit a rough idle.
If the engine's getting too much EGR flow at idle, cruise, or cold operation, the engine could stall after start, the engine could stop at idle after deceleration, the car could surge during cruise, or the engine could exhibit a rough idle.
Thread Starter
Intermediate
Joined: Oct 2005
Posts: 26
Likes: 0
i think i got it
Well after reading everything i put my finger in the tB and it was black so i moved all the moving parts i could see on the TBthen i disconnected the battery and waited then connected it started it up and it was fine can i spray TBcleaner in and around instead of taking apart thanks for all the help
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Originally Posted by hog117
Well after reading everything i put my finger in the tB and it was black so i moved all the moving parts i could see on the TBthen i disconnected the battery and waited then connected it started it up and it was fine can i spray TBcleaner in and around instead of taking apart thanks for all the help
Le Mans Master
Joined: Aug 2004
Posts: 5,141
Likes: 7
From: Metairie Louisiana
hesitation
I chahged the fuel filter and cleaned the throttle body with carb cleaner and that seems to have help some. It wasnt stalling this morning. Maybe still hesitating. It's hard to check because it only does it when cold. Should I dissamble the throttle body and clean it apart? If so how and what should I look for? What is the IAC sensor? Where is it? How do I check it? How do I check the TPS?
http://forums.corvetteforum.com/show....php?t=1343675
http://forums.corvetteforum.com/show....php?t=1351435
Thanks
http://forums.corvetteforum.com/show....php?t=1343675
http://forums.corvetteforum.com/show....php?t=1351435
Thanks
Team Owner
Joined: Oct 2000
Posts: 96,443
Likes: 9
From: Fort Knox, KY
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Start by cleaning out your throttle body (TB) and Idle Air Controller motor (IAC). I did mine last weekend and it cured both my high idle problem and my stumble during cold start-ups.
That new Valvoline SynTech Throttle Body Cleaner is GM approved and runs about $2.04 a can at NAPA. Great stuff. Use it and an old toothbrush and a couple of shop towels to get it clean and restore performance.
That new Valvoline SynTech Throttle Body Cleaner is GM approved and runs about $2.04 a can at NAPA. Great stuff. Use it and an old toothbrush and a couple of shop towels to get it clean and restore performance.
7th Gear
Joined: Apr 2006
Posts: 7
Likes: 0
From: Lenexa Kansas
what next?
I have changed the IAC, ECM, plugs, cap and rotor, all intake manifold gaskets and the car has been to a vette garage BUT it still has cold idle fluctuation until it's warm. Any other ideas? Anyone?
Le Mans Master
Joined: Mar 2004
Posts: 8,700
Likes: 298
From: Ft. Lauderdale Fl
Originally Posted by cantgrowupyet
I have changed the IAC, ECM, plugs, cap and rotor, all intake manifold gaskets and the car has been to a vette garage BUT it still has cold idle fluctuation until it's warm. Any other ideas? Anyone?
7th Gear
Joined: Apr 2006
Posts: 7
Likes: 0
From: Lenexa Kansas
I'm sorry. I added some info to my profile. I have an 84 corvette with a 96 body conversion. I have taken it back to the shop "Corvette Village" to see if they can find anything.
Thanks for the reply! If you have any helpful tips - I will pass them on.
Well - they have not got the answer yet. Now we have changed the prom chip with some improvement but it still idles funny.
Could there be a grounding problem???
Thanks for the reply! If you have any helpful tips - I will pass them on.
Well - they have not got the answer yet. Now we have changed the prom chip with some improvement but it still idles funny.
Could there be a grounding problem???
Last edited by cantgrowupyet; Jun 19, 2006 at 12:03 PM.