# COLD hesitation / stumble



## rcubed3r (Feb 2, 2010)

I have a 2005 GTO with 37K miles that is bone stock except for electric exhaust cutouts.
A few months ago it started stumbling a bit within the first few minutes of starting cold.

If I go out in the AM and start the car and tap the throttle for just a 1/4 - 1/2 second and then release the throttle, the car stumbles, hits 1500 RPM or so, and then drops back down to idle. I should probably post a video so you'll know exactly what I am talking about. I am not sure the RPMS change until I let off the accelerator, like something is moving too slowly.

Once the car warms up for maybe two minutes, it runs perfectly fine. Power is fine, idle is fine, everything is great.

There have never been any codes set on the car.

I removed a K&N intake and replaced it with a factory air box since this has started and it did not help at all.
I have replaced the spark plugs, cleaned the throttle body and the MAF, and nothing has helped.

I ran a Superchips tune on the car since I bought it ~3 years ago. I removed the tune about a week ago, reverted to the stock tune and it still has the problem. I removed the battery for a few hours and reconnected it with no changes noticed.

Any ideas?

This may be unrelated, although I hope it is completely related-
Since removing the Superchips tune, and when the car is cold, if I am driving and the car goes to change gears, the transmission drops out of first, the RPMS drop like mad, and then 1/4-1/2 second later the car changes to second and the RPMs come back. ONLY when it is COLD COLD. It's like the PCM is retarding the snot out of the spark when it is changing gears. This was completely unnoticeable with the Superchips tune.
Tranny fluid looks and smells like new and always has been full.

I would really appreciate any help. If someone wants a video, I'll be glad to post it once it warms up here a bit.

Thanx,
Ron


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## Shorty29 (Jul 31, 2009)

Check your Idle Air Control screw on the throttle body housing. You may have to give it a 1/4 turn or so. That controls where the throttle blade is held at during idle or no throttle operation. It'll raise your idle RPMs some but it should cure the stumbling/hesistation issues you're having.


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## Gotagoat (Jan 6, 2006)

Most engines will stumble occasionally if blipped when cold. Since it's okay after a minute or two, I wouldn't think you have a problem. In cold weather in particular, I let mine run for a couple of minutes before touching the throttle and I keep it below 2000rpm until it reaches operating temperature. Probably overdoing it but that's the method I've used on all my engines.


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## GTO JUDGE (May 14, 2005)

Did you put your MAF sensor back in correctly, is the screen obstructed??


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## GM4life (Mar 18, 2007)

Shorty29 said:


> Check your Idle Air Control screw on the throttle body housing. You may have to give it a 1/4 turn or so. That controls where the throttle blade is held at during idle or no throttle operation. It'll raise your idle RPMs some but it should cure the stumbling/hesistation issues you're having.


He has an 05 GTO with drive by wire. Idle is contolled by throttle body motor adjusting the throttle blade. The 04 uses a IAC to maintain idle speed. Besides I would not touch the throttle blade screw on the TB.


Gotagoat said:


> Most engines will stumble occasionally if blipped when cold. Since it's okay after a minute or two, I wouldn't think you have a problem. In cold weather in particular, I let mine run for a couple of minutes before touching the throttle and I keep it below 2000rpm until it reaches operating temperature. Probably overdoing it but that's the method I've used on all my engines.


:agree


When the engine is cold it goes into a cold start mode, the computer sets the engine to high idle mode and richens the fuel mixture. Svede1212 is better at that. If you got no codes and checked everything out like you said you should be fine. My car have a small surge at idle when cold but goes away after its warmed up.


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