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View Full Version : Transmission clunking/ engine revving super high at idle / "driving itself" HELP



ambitious98xj
01-19-2012, 06:21 PM
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 , we don’t wanna blow our engine or get into an accident. Help please if you can!

Thanks a bunch! -Dave

ambitious98xj
01-19-2012, 06:30 PM
I appreciate all replies, thanks everyone.

4.3LXJ
01-19-2012, 10:25 PM
I think all you have is an idle problem. The high revs will make it shift into gear hard. Check your idle air controller. It is on the throttle body. Pull it and clean it. If that doesn't do it, it will need to be replaced. Any check engine light/

T3k
01-19-2012, 10:37 PM
check the hose that goes from your brake booster to the intake manifold if thats removed the brakes get hard to push and as for the clunk did you check your motor and trans mounts

uberxj92
01-19-2012, 11:18 PM
after you do what 4.3l said , try checking your vac lines make sure they are all hooked up & not just hanging around.

prerunner1982
01-19-2012, 11:22 PM
^+1

Cranesrule
01-24-2012, 09:20 PM
Throttle position sensor. This will cause the high idle as well as the tranny clunk. Clean the IAC first, if and when this doesn't fix the issue swap the TPS.

PEI-XJ
11-19-2012, 08:35 AM
i was out wheeling yesturday and mine is doin the same thing be4 it shifts goin to try eveything you listed

cantab27
11-19-2012, 10:48 AM
Throttle position sensor. This will cause the high idle as well as the tranny clunk. Clean the IAC first, if and when this doesn't fix the issue swap the TPS.

x2 on the tps ........place ya bets here folks.....easy fix ..

89Laredo
11-19-2012, 10:51 AM
Tps, vac lines, iac.
Check them before asking for more help,.

PEI-XJ
11-20-2012, 04:32 PM
i replaced my tps today and it is working better then it was

gajeepguy
11-20-2012, 05:32 PM
Did you adjust it properly? Gotta ask!

Clean the IAC yet?

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