Alright all,

swapped a howards asa cam into my sons 2003 5.3, tsp mail order tune (x3 now) won't idle UNTIL you unplug the vacuum line to the brake booster??? it will idle runs not well and his mpg is around 3.5 mpg! For the life I can't figure this out. TSP has no clue, any thoughts. new maf, o2 sensors in since swap. I am out of ideas. thanks

 

That means it's dumping fuel.

Take it to someone who can tune it in person.

 

That's what I told him to do. My idea for tsp mail order to get it close, but NO cigar yet. I am in over my head with tuning and pcm controlled trucks (for now) thanks for the reply!

 

If all you did was a cam swap it should run on a base tune. Just don't beat on it.

 

could be a problem with the idle air settings in the tune, I would imagine an idle relearn needs to be done, especially after I am assuming send the pcm out, I have seen bad iac motors cause a similar issue where vehicle wouldn't idle until a vacuum leak was created to allow for more air to be pulled in

 

Does the car run better if you unplug the MAF? Was the MAF used or look broken?
Did you change injectors at the same time?

 

in for the conclusion.

 

We swapped the throttle body and boom, now it idles! now to send the pcm back to tsp because the first tune they did was probably right. thanks for the help all!! He did have a random code awhile back for the tps I think, but none since? stay tuned for a final answer after another tune.

 

I've read where people drill a small hole in the throttle blade to help it idle.

 

Sounds like the culprit was a bad iac or possibly tps, considering its an 03 i am going to assume it was a dbw tb.... Which essentially means 2 iacs..