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High idle and trans shifting high

D

doublestack

NAXJA Forum User
Location
wellington,co
Im working on an 89 XJ with 4.0. I have been fighting a high idle and the transmission shifting at 4000RPM's. I have removed cleaned and replaced TPS and the Idle air sensor with no change, I have takin starting fluid and sprayed most of the vac lines in the engine compartment and havent found any leaks. Is there a vacum shift selnoid on the transmission, and if this is it could it cause a high idle?
Thanks for any info
Joel
 
No vacuum to the AW4. There is a throttle pressure cable from the TB to the AW4.

Pull the 10 amp in-line fuse in the yellow wire that runs to the TCU, passenger's side of the dash under the glove box. Then try shifting the trans manually. If that works then the problem is electrical, TCU, harness, solenoids, NSS possibly (it does a bit more than just keeping it from starting in gear).

What are you calling a high idle? 700-750 rpm, in DRIVE, engine and trans fully warmed after about 20 minutes of operation.

The IAC is a stepper motor, not a sensor. Rather than provide data to the ECU, it responds to the ECU's commands. Have you adjusted the TPS?
 
It is running up around 2200 RPMS. After reading a few other post I read something about good battery connections. I have chitty at best connections right now, but will be fixing that tomorrow. Maybe that is what is causing all my headaches. This forum is loaded with good info.
I will also try the fuse if the battery connection doesnt fix it. I get my meter back tomorrow so I will chek the TPS.
 
The most important ground connection is from the drivers side rear of the head to the firewall.
 
joe_peters said:
No vacuum to the AW4. There is a throttle pressure cable from the TB to the AW4.

Pull the 10 amp in-line fuse in the yellow wire that runs to the TCU, passenger's side of the dash under the glove box. Then try shifting the trans manually. If that works then the problem is electrical, TCU, harness, solenoids, NSS possibly (it does a bit more than just keeping it from starting in gear).

What are you calling a high idle? 700-750 rpm, in DRIVE, engine and trans fully warmed after about 20 minutes of operation.

The IAC is a stepper motor, not a sensor. Rather than provide data to the ECU, it responds to the ECU's commands. Have you adjusted the TPS?
Click to expand...
Well I think its the TPS, we checked it and it didnt change much on the multimeter.
As for the tranny I disconnected the fuse and the tranny manual shifts great. Is the TCU that block looking thing under the passenger dash?
 
That's the one. Sounds like you have an electrical issue for sure, what output range did you get on the TPS? It should be approx 5V on one pin and a smoothly varying voltage on another pin as you sweep the throttle from idle to WOT.
 
0.8 sounds like a good low value, but I believe the value at WOT should be around 4 something. That would definitely cause your shifting issues if the TCU thinks the throttle is way lower than it really is.

EDIT: I see you already replaced the TPS - measure input voltage? It should be around 5 volts if I am not mistaken. If this value is off, your MAP sensor and other sensors will also produce skewed readings.
 
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