High Idle with 1998 GMC Jimmy

Driving home this evening, noticed that the Jimmy was idling very high. So high in fact that I did not need to press the accelerator. Luckily I was on the beltway so braking was not too much of an issue.

With car in park, engine is idling anywhere from 1500-2000 RPM. This just started while driving tonight - no problems like this before.

It's almost like the accelerator is stuck. I get no relief from the high RPM by going through the gears. Does not seem to be a tranny issue.

Is there a vacuum hose or a sensor that I can test before calling a mech?

Thanks in advance,

Malcolm

The first thing to check is throttle linkage at the throttle valve on top of the engine. Make sure the linkage goes all the way to the stop. (It should be spring loaded to the closed position.) You can check this with the engine off. When the engine is running, you can try kinking the vacuum hose to the power brake booster and see if that brings the idle down. If it does, you need a new booster. Is the "Service Engine Soon" light on yet? If/when it does, advance auto and autozone will scan trouble codes at no charge. Write them down and post the codes here, we can help you with the diagnosis.

The vortec engines are notorious for their leaking intake manifolds too. depending on where the gasket decides to go it could suck coolant or air. get a long rubber hose and listen around the plenum when the engine is running for an air sucking sound. just be carefull of the belts whiles youre checking this

Looks like i've got a little of both. There is about a 1/8 inch gap between the linkage "plate" and the screw stop. With engine running, I can push the lickage towards the stop and the idle does slow. It returns to it's previous high-idle position when I release.

Removed vacuum hose from booste and kinked. Engine did not idle as fast (1000RPM) but still was higher than it was prior to this problem.

Can I attach pictures here? I took shoots of the linkage just as reference material.

Thanks to all for helping me out with this.

I just had the same problem with my 1996 Jimmy... It was the throttle senseor... It cost me $40.00 to take care of the problem...