Idle and TPS issues

[rodteixeira]

Hey there

I have an auto XJ '98 4.0L and i've been having issues with the idle.

It idles around 1500-1600 rpm in park and neutral. And it goes down to 700-800 in drive and R.

recently rchanged the TPS and the idle Was fine, until few days ago started to go up again whe put in P and N.

IAC and MAP are new aswell.

Testing the TPS signal wire throws 2.39 volts at WOT. I know its supoussed to be under 4.49 volts but is that low normal?

The idleling issue stills. When park, and press gas pedal it goes down to 700 rpm.

I dont know what is actually happening. Any ideas what shuold I try?

Note: the airbag ligth is on. The horn is bridge to another button placed at the side of the sterring wheel. All the clockspring wires are unplugged except for the bridged horn wire. Turn signals are working, sometimes they blink fast and sometimes they blink slow.

 

[wbnickens]

Leaking throttle body gasket or butterfly shaft seals?

 

[Tim_MN]

The TPS should range from about .25 volts at minimum throttle opening (idle), to 4.5 volts at WOT wide open throttle.

Unplug the horn relay and/or fuse and then re-test.

2.39 volts is out of tolerance and presumably a short circuited or defective TPS.

Crown Automotive, OmixAda, and Duralast are cheap crappy parts and are often out of specification or dead right out of the box. Genuine Jeep TPS are best, NTK are also good.

Cheap parts are cheap for a reason.


TESTING: Unplugging a faulty Clock Spring should return the TPS voltage to its’ normal readings. Or, you can remove the Horn fuse in your fuse block - this will remove the 12 VDC supply to the clock spring. Once the short circuit is temporarily disconnected, you should be able to reset the trouble code, and confirm you diagnosis of a faulty clock spring or faulty TPS.

CAUSE: The Switch Sense circuit in the Clock spring in the steering wheel hub has shorted to battery voltage from the horn button circuit. When the Switch Sense Circuit shorts to the 12 volt HORN circuit the TPS signal voltage is driven high and remains there as shown. This is because the 5 volt reference voltage used by the Cruise Control “Switch Sense” circuit and the TPS are shared inside the PCM.

CORRECTION: Replace the Clock spring assembly. Once the Clock spring has been replaced be sure to check the sensor 5volt reference voltage at the PCM to insure that circuit has not been damaged by the short to power. Also check the TPS signal range to insure the TPS has not been damaged.