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LS1 Cold start problem

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Old Dec 2, 2009 | 01:57 PM
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Default LS1 Cold start problem

Over the past couple of months my car has been acting funny on cold starts (6-7+ hours of sitting). It will start normal, but then act like it is stumbling and will drop down to 8-900rpm, then surge quickly back to ~1700-1800rpm. It usually does this twice before it settles down to normal. Also, when it is revving itself up the exhaust sounds "crackly" or as if it is misfiring or otherwise running funny.

I know these aren't very good details, but it's on a 98 LS1 with full tune, 228/230 cam, etc.

Any advice is appreciated, can take a video if needed
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Old Dec 7, 2009 | 02:09 PM
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bump ^^^
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Old Dec 7, 2009 | 04:21 PM
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Do you leave a trail (big or small) of bluish-white smoke when you nail the gas from a steady cruise speed of like 50mph?

.
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Old Dec 7, 2009 | 04:38 PM
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Vacuum leak.
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Old Dec 7, 2009 | 09:34 PM
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Not sure about the smoke, but also sometimes on warm starts the car will have trouble idling (starts fine, then rpms dip down really fast, lights flicker, etc. Then surges back up to normal). I had it checked for a vacuum leak and the mechanic said he didn't find one, but that does sound like the cause of my problem
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Old Dec 7, 2009 | 10:42 PM
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Clean your MAF. Your MAF is what handles the engine on cold start up till it gets warmed up...then the 02 sensors take over.

Your MAF could wacky and causing your IAC valve to freak out. That would cause your rpm's to jump around until it gets warmed up.

Also, spray the **** outta the IAT sensor in the lid with the MAF cleaner while your at it.

Pretty cheap thing to try before you start really digging into it.

.
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Old Dec 7, 2009 | 11:02 PM
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Is the check engine light on??
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Old Dec 7, 2009 | 11:09 PM
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MAF and IAT sensor for sure. Mine did the same thing and cleaned those and it stopped.

Exhaust is normal until its warmed up. Mine always pops when I shift until its warmed up.
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Old Dec 7, 2009 | 11:54 PM
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Originally Posted by LS6427
Clean your MAF. Your MAF is what handles the engine on cold start up till it gets warmed up...then the 02 sensors take over.

Your MAF could wacky and causing your IAC valve to freak out. That would cause your rpm's to jump around until it gets warmed up.

Also, spray the **** outta the IAT sensor in the lid with the MAF cleaner while your at it.

Pretty cheap thing to try before you start really digging into it.

.
My MAF is disconnected and I don't use my 02 sensors either, I believe I have an SD or static tune of some sort. Can you diagnose a vacuum leak with a diagnostic tool such as AutoTap? I believe last time I was in the shop my IAC was stuck between 130-150 count, so I should probably replace that sensor
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Old Dec 7, 2009 | 11:59 PM
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Originally Posted by paulc87
My MAF is disconnected and I don't use my 02 sensors either, I believe I have an SD or static tune of some sort. Can you diagnose a vacuum leak with a diagnostic tool such as AutoTap? I believe last time I was in the shop my IAC was stuck between 130-150 count, so I should probably replace that sensor
Well, there is only one way for an engine to rev up....air must be getting into the intake. Adding fuel won't make the engine rev up..without air to go along with it.

So your IAC is probably wigging out. Why...it could be anything from a failing IAC or a PCM problem to a short somewhere. Something is opening the IAC.

I don't know if a failing TPS sensor or IAT sensor can cause the IAC to freak out, but maybe.

.
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