I have a 2000 15000 5.2 when I first start it the engine will rev up and down for 15-20 sec and then smooth out, I will also get alot of white exhaust which I am hopeing is just water vapor. It clears up after a little while. When I start out it seems to run rough, once it gets warmed up it runs great. I am thinking either TPS or IAC problem. Am I on the right track?

 

is it cold where you are?

 

yes I live in Northeast PA it didn't get above 32 today

 

its also been cold where i live in pa.. my trucks been doing the same thing.. what i mean by that is until it warms up to all but running temp it has "white smoke" which is condensation. however, my truck doesnt usually seem to have an idle issue on start up, on occasion it does but it has to be sitting for a long time and extremely cold. But like you said it goes away within like.. 20 seconds.

 

try running some seafoam in a gas tank to help with the idle and do not worry about the water vapor when you start up

 

iac contols i at idle but the sugering sound like a TPS.... frist i would clean the iac and the port that it goes into.

 

If your talking about fluctuations on startup, I had the same problem a two years ago and am still wondering what caused it. I cleaned my entire TB, replaced both sensors (IAC twice)... Did my tune-up. Nothing seemed to help but kept going with the mod's and either I have gotten used to it doing it, or... it has gone away. Not too long ago I did have a blowing white smoke problem on startup which never happened before. A Huge cloud of white smoke came out as the engine stumbled when you tried to start it. None the less it fixed itself after a few days and some new gas. Been going strong for months now with no sign of any more problems (knocks on wood). If you do find out what causes that fluctuation, please... please... do post the answer. It has been my fear for the past year that I have a cracked head. Mine only seemed to fluctuate three times startup. Best I can describe is it starts up, high idles, then starts to drop. sounds like engine starts to miss and rev's to compensate.... (then another gradual drop, rev, gradual drop, rev) Like I said mine only did it three times after being started. I found that if you rev it during its "problem cycle" it doesn't continue to do the fluctuations but idles fine.