Over Revving

[MJchick]

My MJ has a bad habit of occasionally over revving on me. It does it sometimes when I start it, it will rev out to max. and it is really scary when it does it while I'm driving. I don't notice it till I go to shift gears. While it's in gear the R.P.M.'s are normal but the second I touch the clutch it revs up to max and I usually have to pop into nuetral and quickly shut the truck off and coast to the shoulder of the road and let it sit for 15-20 mins before I can start it again with out it revving up. Does anybody know what might be causing this?

[manche]

sounds like a tps prob

[Mitch]

If the pedal is sticking (I just went through this) pop the hood and squirt wd40 all over the mechanisms that control the throttle to the right of the engine if your standing at the grill. Fixed my issues.

[BLHTAZ]

OK...I am going to just copy my response from the other thread to the same questions asked last night by someone else instead of typing the same thing again... ;)

 

 

I just went through this nightmare. Mine was up to running at 3000 RPM. Here is the thread detailing what I went through... http://comancheclub.com/forums/viewtopic.php?t=12188

 

Ultimately, as you will see, my issue was a bad ground. The two most common idle issues are vacuum leaks and the IAC. The IAC has no self tests that I could find, but needs a special tool to test it so you just have to look down in the top of the throttle body while it is running to see if it is closing or not. You can also put a couple fingers over the air inlet hole to the IAC and see if it helps, but be careful as the vacuum at that point is very strong if the IAC is stuck open.

 

I posted in the DIY forum about how to do the test on the TPS if you want to do that too. That is here... http://comancheclub.com/forums/viewtopic.php?t=12260

 

An addition to this post... The TPS is not usually the problem with High Idle, but rather would more likely cause a low idle, erratic idle or stalling. It is possible, just not the first thing to look at in my experience. It is easy to test though so why not get it out of the way ;) .

[BookspanS]

Is it only when you shift gears? Does it happen after you shift and try accelerate? I have a 5-speed 99 Merc Cougar that I had a similar prob with.... Bad clutch

[MJchick]

It has nothing to do with shifting gears because it does it sometimes as soon as I start it. And its not only revving up a little bit it revs up as high as the needle will go which is why I have to quickly shut down the truck until I can start it at a normal R.P.M. so that I don't blow my motor. The only way I notice it when I'm driving is when I let off the accelerater to slow down and instead I'm gaining speed without touching the pedal. The throttle is not sticking we've already checked that out.

[Oizarod115]

an idle air even completely dead shouldn't give you red-line, just about 3k...

 

i wouldn't think thats the problem

[KillerCOM]

None of you sensors will do that. Is this a TBI or multiport 2.5? Do you have a throttle return spring? If its TBI it should have a set of springs that go from the throttle shaft and the bracket mounted to the TB. Thats what it sounds like if your cable isn't sticking. :cheers: