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Bad TPS? CPS? ECU? Fuel Pump? A crappy engine? Maybe you have the answer.

jayo310

NAXJA Forum User
Location
ca
Hey guys. My 99 XJ Sport has been acting funny as of late. With the occasional putt-putt of the exhaust along with the even more occasional cylinder 1 misfire code (sometimes on, most of the time off), my RPMs have just started to act funny.

The putt-putt of the engine usually happens when in park or neutral, but disappears once I put it in drive. It kind of sounds like a steam locomotive train. But this might be a separate issue. Now, my RPMs has been occasionally running rough from 400-700 at a stoplight, and when I throw it in neutral, the RPMs surge to about 1500. When I resume driving, everything feels pretty normal until the next stop light - putt-putts, rough idle, and surging RPMs. It goes away, then comes back.

Another funny thing... When I'm going around 40-50mph and let off the gas to cruise, I notice the RPM dropping like normal, then surges to 1200, then drops again, then surges, so on and so forth. This pattern repeats every two seconds.

I'm totally confused of whats going on here. I've done my due diligence with changing out to champ plugs, cables, distributor, fuel injectors, exhaust manifold, o2 sensors, cleaned IAC, no vacuum leaks, fuel pressure is good, cylinder compression is within range, and TDC is dead on.

Any ideas? I was wondering if its my TPS. I have a mopar CPS waiting for me to install. Thanks!
 
A scanner that shows "live-data" would be a good start to get some real numbers as to what's going on.
Battery voltage is also critical, so besides checking the battery, check all your ground connections.
 
A scanner that shows "live-data" would be a good start to get some real numbers as to what's going on.
Battery voltage is also critical, so besides checking the battery, check all your ground connections.
Thanks!

I have a Bluetooth Blue Driver OBDII scanner that supports some live data. What should I be looking for?

I have checked and cleaned all ground connections. The battery wire terminals could get replaced. They don't look corroded, but do look very very old.
 
The symptoms strongly suggest a faulty IAC. Genuine Jeep or NTK O2 sensors, right ?

The TPS, and the CPS can be tested. Low voltage or voltage fluctuations can cause PCM issues.
 
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