Lately my Tahoe has been having problems with cold starting. In the mornings when I start it for the first time it starts perfectly fine but runs for about 5 seconds and then the RPM's will drop and rise continuously. It will continue to fluctuate until it dies or you give it some gas. After you rev it up it will run fine until the next morning when the process is repeated. Does anyone have any suggestions as to what may be causing the problem. We recently changed the distributor cap and rotor but it didn't fix the problem.

Thanks

 

What year?

More than likely you need to replace the intake gasket. When its cold it shrinks allowing air to suck in the engine and not be accounted for through the MAF. As the engine warms it causes the gasket to swell sealing the air leak.

When its cold and running like crap spray some carb cleaner where the intake meets the heads and see what it does to the idle.

 

Yeah, at any rate, it sounds like some sort of vacuum leak. I prefer to use an unlit propane torch because you can more accurately pinpoint the source of the leak. Starter fluid works, but with less-than-pinpoint accuracy.

 

Really dont need to "pin point" an intake leak. If its leaking anywhere it all has to be replaced. Most vacuum leaks will set a code. The intake leak usually doesnt.