For a while now I've been dealing with a rough idle in my 98 Cherokee Classic 4.0I6 Automatic. The RPM needle bounces around 600-850, the engine felt like it was missing every few seconds, and the exhaust smelled like it was running rich

I've replaced plugs, wires, distributor cap/rotor, and pre-cat o2 sensor. I've also cleaned out the throttle body, IAC housing and pintle, and the hole going to the MAP sensor.

After replacing the pre-cat o2 sensor, the engine doesn't feel like it's running rough any longer, and the exhaust doesn't like it's running rich. However, the RPM needle still bounces. I guess it's not so much of a performance issue, as the needle bouncing is just annoying...haha

Anyway, I was thinking of checking my TPS to see if it is properly adjusted. I've searched on the forums quite a bit and on the internet, but haven't found the exact procedure and specs for the 98 TPS. Everything I've found deals with a 4 pin connector, but the 98 TPS has a 3pin. Does anyone happen to have information on how to test this year?

Hi I sent you a PM that may help you out...Tj

dribbling injector ?

The TPS for a 98 is NOT adjustable. That was only 87-90. But you can test it....

Does the RPM actually go up/down slightly and corrrespond to the bouncing of the tach needle? If your RPM is fluctuating when you are set on cruise or at a steady speed, there is something wrong.

TPS and fuel pressure would be a good place to start (fuel pressure must be tested with a gauge).

Thanks! Any tips on testing the return voltage from the sensor? I was able to disconnect the connector and test wires A (ground) and C (+5v) and it showed good with 5.1v. However...I'm not able to use the test leads on A and B while the connector is plugged in as there is insulation around the wires from the rear. I checked the FSM and I am supposed to have .26v with the throttle closed, and 4.49v with the throttle wide open.

As for the bouncing needle, it doesn't seem to correspond with the actual engine RPM's during idle. It's almost like it can't figure out where the actual RPM's are. Also, the RPM needle is solid when going a constant speed.

iac idle air control motor did you ever clean it

I was a little concerned about plugged injectors to begin with...I've seafoamed the engine, ran a few cans of Seafoam, Techron, and Berryman's B12 Chemtool through the tank. I'm sure they've probably made a bit of difference but not sure how much. Replacing the pre-cat o2 sensor is what made the actual engine idle smooth out.

Yeah I took the throttle body off and removed the IAC motor. Gave the throttle body and the IAC housing a good cleaning as they were both pretty carboned up. Didn't really seem to help too much though.

i re read th e op and i see that if an injector is dripping the idle will in crease with every drop then fall back dow drip idle up fall back downits just an idea