Rough Idle On Start Up

[Scramble]

Aloha!

 

I have a 2002 GMC Yukon, 5.3 L (non flex) with 68k miles, which sits in an enclosed garage all night (in Hawaii). When starting my truck for the first time everyday, the RPM's will rise normally to about 1500 then drop down the hundreds all of a sudden, then the rough idle begins until the engine warms up. I would liken the idle to an engine with a HOT cam in it....sometimes it sounds like it'll die out. The check engine light goes on as well. Once I drive around a bit the rough idle goes away, but the check engine light sometimes stays on or even flashes. (I don't know if there's a difference between a flashing or constant CIL)

 

I took it to my mechanic who had it scanned, and the scanner read a bad MAP sensor. So I replaced the MAP sensor, but the bad idle at initial start up persists. He said it wouldn't be the TPS (one of my guesses) as a bad TPS would act up cold or warm. I was trying to think of what would cause this when the engine is cold, in open loop. I'll try to check my IACV to see if it's dirty, as I've never cleaned out my TB, Intake, like I did with my 96 Impala SS.

 

Anyway, that's where I'm at now. Any input would be appreciated to resolve this as it's a pain to leave my truck at my mechanic's.

 

Thanks alot!

[stublejumper]

air intake temp sensor most likely or engine temp sensor but the iav sensor is a good start just make sure you hold on to it firm and dont turn it down wards when you take it off. one other thing you could try take out the up stream 02 sensor spray them with brake cleaner maybe there getting a bad reading but still in range not to throw a code don't bang on the pipe you could damage the sensor

[Scramble]

Thanks for the reply, jumper.

 

I'll have to go get me a Chilton's for this truck just so I can find the darn temp sensors. If it's not the iac I'll check those out, and move on down the line of things it could be.

 

If you guys think of anything else, shoot um at me please.

 

Thanks again!

[BRZ71]

Intake manifold gasket. Mine did the same thing and it had an air leak. I never could find the leak, but after the gasket was changed it never did it again. Mine was wost on cooler mornings.