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Transmission clunking/ engine revving super high at idle / "driving itself" HELP

ambitious98xj

NAXJA Forum User
Location
Portland, OR
Transmission clunking/ engine revving super high at idle / "driving itself" HELP

So we’re having some issues with our 1990 XJ Limited w/ 4.0 non-High Output, Automatic.

At starting, it’s revving between 1,500 – 2,000 (600 is normal for us as of yet)

When shifted into Park, the RPM’s rev very high (well above 2,000), as well as makes a loud “ka-thud” sound when shift into Park or Reverse.

When driving, it shifts with a clunk and a soft jolt (this was happening mainly shifting into Drive)

RPM’s seem to be in the normal zone when driving at freeway speeds.

Idle is raising “by itself”, carrying the Jeep down the road at a speed upwards of 20 mph without touching the accelerator. When this was happening, it was also very hard to brake, really had to push down on it hard, and it crawled to a stop, very slowly. Release the brake, and the Jeep goes forward still at much greater force than normal idle, as if idle is sticking.

When we just parked it, the idle was upwards of 3,000 RPM, in Park.

Hoping someone out there has some input to this dilemma L we don’t wanna blow our engine or get into an accident. Help please if you can!


Thanks a ton,
Dave.
 
Re: Transmission clunking/ engine revving super high at idle / "driving itself" HELP

Idle Air Control is the first thing I'd look at, being that it is an idle problem. If the rpms are high then a clunking transmission is normal. I call it neutral dropping into gear. Good way to break the trans. Don't ask me how I know this, just know that I do. :)
 
Re: Transmission clunking/ engine revving super high at idle / "driving itself" HELP

Poor brakes and high idle tend to say low vacuum. It sounds like you have a leak, possibly a bad vacuum booster. Take a pair of pliers when it is idling real high and crimp the vacuum line going to the booster and see if the rpm's drop.
 
Re: Transmission clunking/ engine revving super high at idle / "driving itself" HELP

Plus 1.

Check all those hoses and tubes. Vacuum leaks can be difficult to isolate.

This sounds to me like you don't need to worry about your transmission being a problem. Yet.
 
Re: Transmission clunking/ engine revving super high at idle / "driving itself" HELP

Plus 1.

Check all those hoses and tubes. Vacuum leaks can be difficult to isolate.

This sounds to me like you don't need to worry about your transmission being a problem. Yet.

I agree, and note that those hard to find vacuum leaks SUCK!!!! LOL:roflmao:
 
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