99 Jeep Cherokee Sport, 4.0

Someone please answer this question clearly as I'm about to throw myself in front of a bus from the frustration.

I've tried everything I can think of. The engine still revs itself while idling up to 3 on the gauge. The tps is new. Am I supposed to somehow adjust the damn thing or not?? I've watched all the videos I can find. Some say adjust. Some say there is no adjustment. Some show two plugs instead of just the one that plugs directly onto the tps. I don't have two. I have one. Just one. Even if I loosen the tps screws I can't move it or twist it around to change voltage. All I can do is tighten it straight back down again. So what is the answer?

 

No adjustment needed for that one.

More importantly, it is not the cause of your 3k RPM at idle. It only measures how open or closed the throttle plate is which is used for a variety of purposes by the computer.

Idling up to 3k means you have unwanted air getting into the intake manifold. The most common cause for idles that high is that the last time the intake manifold was removed/reinstalled that it got hung up on the rear locating dowel and back section is not sitting flush against the block. Is this a possibility in your case?

Intake manifolds that have worked themselves loose can also cause this. The IAC controls the mechanical aspect of idle RPMs (controls how much air gets through the throttle body when your foot is off the pedal), but even when it is stuck open (failed, but it is more common for them to be stuck shut - leading to a no start condition) it normally doesn't cause 3k RPMs.

 

No adjustment. Can you choke out the engine by covering the throttle body?

 

3k sounds more like a leak. Is the throttle plate closed with the tps installed?

You can adjust the throttle valve cable easily. Press in the button and push the plastic end back toward the passenger side. Then fully depress the gas pedal to extend it to it's proper operating range.

I don't think that's your issue though.

Btw you could try unplugging the IAC and see if your idle changes.

Did you take the throttle body off to replace the tps?

 

Thanks for the responses. In response :

I've had the car since it was about four years old. I've never had the intake manifold removed. I tried to see if the bolts are tight using a torque wrench, but there does not seem to be enough room to get the wrench on the bolts. I'm not sure how to proceed with that. Also, bolts are rusty, and I'm concerned about breaking them off even using the correct torque setting.

The IAC is new. I removed it anyway to check the o ring. It was squashed from having been compressed when the screws were tightened, but otherwise looked ok.

The throttle plate is closed with the tps installed. I smoke tested and saw a small leak from around the throttle body shaft, but this wouldn't be enough of a vacuum leak to cause these problems, would it? I have not tried choking out the engine by blocking the throttle body. I'll do that tomorrow.

I had already tried adjusting the throttle cable. Made no difference.

Yes, I did remove the throttle body to replace the tps, iac, and map sensor. The gasket was in good shape.

Tomorrow I'll try unplugging the iac and see how the idle changes. I'm not sure what the point of doing that is, but I'll give it a try.

I tried testing with a vacuum gauge again. Same result. The gauge reads 13 while the engine is warming up then goes up to 22 when the engine revs itself. I assume all that tells me is that there is an air leak somewhere.

 

The throttle cable that is adjustable is for the transmission shift points anyway. Try disconnecting the throttle pedal cable and see if it idles normally. It's possible it's hung up inside and holding the throttle open slightly. There was a case not so long ago where there was a wire harness under the dash not allowing the pedal to return to idle. Also disconnect the cruise cable if you have one.