97 Sport has been just fine then all of a sudden, it starting surging in cruise control. Then, with cruise control off, the speedometer started fluctuating up to 5 mph to either side of actual. I have a check engine lite for idle air control but these issues are happening in the 60 mph range. I did unplug and replug IAC, Mass air sensor and and intake plug and it got better. I am suspecting a Mass Air Sensor issue but will replace the IAC with Mopar this time. The idle is 1200 which is a little high. Appreciate any responses.

 

As I accelerate to 30 mph, the speedometer jumps 10 to 40 mph higher then returns to actual. This makes cruise control surge as well, but the manual gas pedal works OK.

 

idle @ 1200RPM is possible indicative of a failed TPS

try unplugging it, if nothing changes, that will be the culprit

 

Thank you for the reply. Yesterday, I did the "trip sensor down/key on" test and the speedometer did its trick in steps up to max and back to 0. It was fun to watch.

also touched both battery cables together 30 sec to 0 out the computer. I haven't started it up again

BUT before that while idling, I unplugged the plug on the back side of the air intake (TPS?) briefly and the idle surged up. When I re-plugged it, the idle went back down. My check engine code says it is the IAC and I haven't replaced it for $80 Mopar and I am not convinced that speedometer fluctuations at 60+ mph have anything to do with the idle. I welcome more replies.

 

Post computer zero, I took the jeep for a test run today and the speedometer is good. We'll see if it stays and if the IAC check engine light comes back. If it is good, it is due to your helpful suggestions. Thanks

 

Speedometer still fluctuates, sometimes wildly but stabilizes as it warms up. I read that someone replugs the wire into the back of the speedometer annually to prevent this. A youtube showed the easiest way to access the speedometer is to remove the dash cover- although the cherokee was older than mine. Any ideas on the above?

 

On my 2000, the Speedometer fluctuating after my airbag light came on for the clockspring. Then I started the Jeep up the next morning and the horn stuck and it ran poorly and would surge with no check engine light. I tested everything for a few days until I found a thread on here about a 98 with a similar issue. It wasn't until I disconnected the horn relay and the airbag connector on the dash support under the column going to the clockspring.

So possible tell tale of a clockspring on the fritz.