Pontiac Repair: 93 Pontiac Transport 3.8, chevron techron fuel system, throttle position sensor

Question
I have a 93 Pontiac Transport 3800 .
The car does not run smooth when at an idle,seems to be misfiring, and has excess water coming out of exhaust.(it is definitely water not anti-freeze)
I have recently had the lower intake gasket and upper (plenum) replaced. The mechanic assures me there is no coolant leak.
I have also changed spark plugs and wires and replaced TPS throttle position sensor. Car runs fine at speeds above idle.

Answer
Hey Pete:

Condensation out the tail pipe is not unusual especially if it's extremly humid and at lower temps. I would look for a vacuum leak on this car also make sure it has the correct PCV valve in it and not a aftermarket "fits all" ther are 2 vaussum line sthat run off the front of the engine just above the drive belt make sure there are no leaks in either of those lines. Why was the TP sensor replaced? was that an aftermarket part? If so then it could have the wrong reading going to the engine computer at idle and cause your issue again a fits all part is not the right part for this the fits all ones have adjustment built in to them and the factory ones do not if it's adjusted incorretly that could be the issue did it crop up before or after that was replaced? I don't care what car you drive any emission part should be replaced with original equipment parts wether it's a GM,Ford,Toyota etc..... sometimes the cause more problems then they fix. You may also want to try a bottle of Chevron Techron fuel system treatment in the tank and see if that helps. Good Luck :)