Jeep Code Question

I have a 1998 Grand Cherokee, 6 cylinder and on Saturday it seemed like it was idling a bit rough. Well on the way home from an errand, the check engine light came on so I pulled out our code reader and it gives me a P0121 - something about accelerator sensor/A circuit whatever and performance problem. Cripes - does anyone know what I should check first? I honestly don't know where to start, but the plugs, wires, oil and filter, tranny fluid were all just changed within the past month and it's been running fine until this past weekend.

Any suggestions would be greatly appreciated!

In so many words, TPS signal does not correlate to MAP sensor signal.

Most likely, the TPS (Throttle Position Sensor) signal is low. You can proceed to test it with a multimeter or just replace it. They are around $27 and you need a Torx screwdriver to remove the screws.

[discretesignals]

Hi Stephanie,

I recently had a customer with a Dodge Dakota with the same code and condition that you had.  Unfortunately, the problem is very intermittent.  Did you have any other codes set besides that one?  The funny part about DTC P0121 is that it doesn't aim to a specific sensor but is concerned with the throttle position sensor and the MAP sensor' signals after 1600RPM.  Basically it is a rationality error between the two sensors.  When the throttle position sensor voltage signal increases as you open the throttle the PCM is supposed to see the MAP sensor voltage signal go up also.  The MAP sensor monitors the vacuum inside the intake manifold and the TPS monitors the position of the throttle shaft.  If these two signals don't agree with each other within a specific preprogrammed range in the PCM's look up tables after 1600 rpm, the PCM will set the P0121 code.  I have not been able to determine what is at fault with my customer's truck since neither sensor is checking bad.  I did clean engine and computer grounding points just to see what happens.  My customer told me that it happens only if she is 90 miles into a road trip.  I do know that it could be either the TPS sensor, MAP sensor, or PCM causing the problem.  If you run into any more information from other people on here or other places, I would greatly appreciate any info you could provide me.  I am sorry I can't give you a solution to your issue.  I do recommend that you check the functionality of the MAP and TPS sensors.

Sorry Grease Monkey I was typing up my reply when you posted yours...lol.  At least we are on the same boat with this one.