1998 Sport 4.0, Auto 2WD.
Upon start up it often runs at 1500-2500 RPM and throws a CEL (P-0121 Throttle position sensor voltage does not agree with map) and (P-0700 Transmission fault).
I have verified good grounds and no vacuum leaks.
I replaced the TPS sensor and no change. Replaced IAC and MAP, no change.
Tried a throttle body from the wrecking yard, no change.
Purchased another TPS sensor (Mopar), no change
Removed clock spring, no change
Unplugged each sensor on the transmission one at a time, no change.
Sent the ECU out to be tested and repaired, but no faults found.
Swapped fuel injectors, no change.
The TPS sensor tests fine when back probing the wires and doing the procedure outlined in the service manual, but once the Jeep is started and with the engine running the scanner reveals weird voltages. It's registering 3 volts at idle when it should read .730v and the computer thinks the throttle is opened 74%. If I turn the Jeep off and back on it sometimes will show the throttle at 0% where it should be, but the problem always returns.
Please, if anyone has any ideas as to what the problem could be I would really appreciate it.
Transmission control module, possibly? Screen shots of the scanner below. Sorry for the glare. Thanks for looking!

Paul

 

Forgot to mention that my scanner won't communicate with the transmission. I figured maybe the Jeep isn't new enough to have that feature. Is that true?

 

So the voltage looks correct when backprobing it, but the computer is reading a different voltage?

 

The scanner reads a different voltage once the Jeep is actually idling. With the key on, engine off the voltage looks okay.

 

You might try this.

https://cruiser54.com/?p=60

 

Thanks. Yeah, I have cleaned two different throttle bodies and IACs. I'm pretty sure it's a module or wiring problem at this point.

 

shade tree mechanic at best here...

Can you back probe the TPS input at the PCM while off and then running as compared to the TPS itself. You may have a short or a frayed area in the wire....just a thought....more like a guess....

 

In my experiences the codes from the OBD are only a place to start
This is my drill, because I'm bad at guessing - get your shop manual. Assuming your air filter is clean, spark plugs, cap & rotor and wires are good, check for dangling wires grounding. The wires coming up from the O2 to the fuel rail wiring harness are a good place to start. Then open your shop manual and test your sensors: the temp sensor, idle solenoid, MAP and TPS. In my experience, the crank position sensor is good - or you stranded by the side of the road - but test it anyway. If they are good and your throttle body is clean, move to the injectors: clean them and test the resistance for each one. You can pull them and use a 9v battery to produce a click unless it's defective.

It's MUCH cheaper to test then replace parts till it works right

 

I found the problem! and I feel ridiculous for not having found this sooner. What an unbelievable ordeal this has been. I discovered one of the main connectors near the dipstick had water inside and a few of the pins and cavities were corroded. I cleaned everything and now all is fine. Thanks for all the replies and great suggestions.

 

Yup, that would do it. I'd look at other connections too as that looks like the victim of a pressure washer.