Guys, I'm having trouble finding the source of my problem. 2003 Tahoe 5.3L with 127,000 miles. I think it's a flex fuel vehicle, but I never run any E85.

Cold starts seem fine. Normal driving seems fine, even in bumper to bumper traffic (frequent stops and warm temperatures). It might have some slight hesitation occasionally. The obvious problem: If I stop the engine and run into a gas station, restaurant, etc., and then return while the engine is still relatively warm to start it, it will surge from normal idle down a few rpms and back to idle (almost like an old school hot rod cam, but not not quite). It really doesn't surge past idle much unless it slightly overcompensates when the idle drops low. If I put it in gear after this without hitting the throttle any, it will surge forward or back depending on if it's in D or R. Again it reminds me of an aggressive racing cam, kinda. Once I hit the throttle, I'm generally good to go. I can usually then take my foot off of the throttle and it idles like a dream again. Generally speaking, it is a warm start surge that goes away once I give it throttle once (with a possible touch of occasional stalling).

Here's what I have done: new plugs and wires, clean injection system, and cleaned induction (throttle body) system. No codes thrown. It also had a new gas cap and purge valve put in a few weeks ago due to a code, but I had the idle issue prior to and after that. My mechanic friend suggested new front O2s, but I don't want to sink more into guesses at this point. It isn't my primary driver, so I can live with it, but would like to fix it if I can.

Thanks for all your time.

MP

 

Welcome to the forum.

When you cleaned the throttle body, did you also do the idle air control?

 

Thanks.

It is drive by wire and doesn't have an IAC valve (I'm 90% sure).