Throttle surging when coasting

Hey all, I noticed my '99 XJ (auto, 4 liter, 150k miles) surges a bit when I'm off the throttle and coasting. I only noticed it recently when my muffler was off (could hear the exhaust surges) and can see it jumps from ~500-800 RPM. I don't see this behavior at idle, under acceleration, or when braking--only when the car is moving without my foot on the gas. I'm not aware of any check engine light or codes being thrown either (haven't hooked it up to a code reader, but there's no check engine light). Anyone ever experience similar issues? Could this be a sign of the TPS going out, and if so is there an easy way to test it? Thanks!

Put an analog voltmeter on it and check for smooth needle movement with no jumps.

I agree with winterbeater.....testing your throttle position sensor makes sense. Analog meter works best, manual will have the exact procedure.

There certainly are other possibilities, but the TPS comes to mind first.

After that, I would verify exact fuel pressure on the schrader valve on the fuel rail with a gauge. With your 99, you are looking for 49.2 psi, plus or minus 5 psi.

Good luck and let us know what you find!

Check this out.

http://www.naxja.org/forum/showthread.php?t=1031838

Interesting, so it might just be normal behavior? I'm planning to do a full tuneup of spark plugs, wires, distributor, etc. pretty soon so I'll see if I can test the TPS at the same time too.