Original engine and transmission in this GC which we have had since new.

This recently started happening. After starting, just touching the gas pedal lightly causes the engine to hesitate. It has never stalled, just slows down. It happens in Park and when in gear. On the other side, when letting off the gas pedal, it sometimes surges (revs up). Occasionally it even causes the transmission to downshift momentarily.

No CEL and no stored codes.

The idle speed seems to be higher than normal (1100-1200 vs. 800).

Thanks for any ideas.

 

I would suspect a vacuum leak first. Could be a leaking hose, EGR valve or intake manifold gasket. Check Youtube for how to videos.

 

Thanks, Cougar41. I agree that it sounds like a vacuum leak. So I used carb cleaner (on a cold engine) and sprayed around the vacuum lines that I could find. (I think there are several that I could not find or get to.) The engine purred smoothly during the whole procedure - no rpm changes that would indicate a vacuum leak. The problem has worsened to the point where the slightest touch on the gas pedal makes the engine stall now.

 

Have you check or replace the throttle position sensor? Since the problem is with touching the gas pedal.

 

Thanks, Master Tech. I will give that a try. Probably tomorrow at this point.

 

Check TPS? Here's how: http://troubleshootmyvehicle.com/chr...he-tp-sensor-1

 

Just did the TPS check. I got a smoothly changing voltage of 0.8 to 3.9 volts DC as I positioned the throttle from full closed to full open. Similar results as it went closed. I also did the screwdriver tapping and saw no changing or variation.

Do these voltage values sound reasonable?

Thanks!

 

OK, so after restoring everything to normal following the TPS check, I thought I would start the van and see what might happen. It started, ran, and revved like any normal vehicle should.

Is it possible that exercising the throttle fully open several times cleaned some internal gunk, corrosion, or gunk from the TPS and associated circuits? Admittedly, I drive this van very easily, so it has probably been quite a while since it saw a fully open throttle.

Thanks!

 

I had a leaking EGR vacuum diaphragm do the exact same thing once. (old 2 piece type) It was an internal leak, so spraying around didn't find anything. Drove me nuts for a few hours.

 

It is possible that the connection was getting weak, as that will cause issues like the sensor itself is bad.
For your own sake of chasing ghosts, go through and clean and grease your all your connections under the hood, you'll save yourself a ton of issues later.