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Replaced TPS, what else could it be?

89xjgrey

NAXJA Forum User
Location
Columbus, Ohio
'89 xj w/4.0 automatic,np242. Heres the deal, while parked giving it just a slight bit of throttle, the engine fluxes from 800 to 1100 rpm back and forth rather quickly. It only does it in that one spot, any more throttle and it's smooth, at idle, it's smooth.

On to the next part of the problem...

While driving normally, when I let off of the gas completely, the xj downshifts fine, but the rpm's start fluxing again, until I get back on the gas. Replaced the TPS, checked the idle speed motor, all fine. The funny thing, while the RPM's are fluxing, the voltage out of the TPS remains the same.

PLEASE HELP.

-Michael
 
Error correct:
Rpm's flux between 1050 and 1250. Thanks.
Also, all intake manifold bolts are tight, and found no obvious vaccuum leaks.
 
There is only one good way to check for vacuum leaks, with a flammable brake cleaner, or carb cleaner. I suspect a vacuum leak, saying there are no obvious vacuum leaks is not enough.

I like to use brake cleaner (make sure it's flammable), then at idle spray it anywhere there could be a vacuum leak, if there is a leak, this will find it. You will know because your idle will change when you spray it at the leaking area.

If this does not work, then you can move on, and say there is no vacuum leaks.
 
If possible when doing the vacuum leak test, try blocking off as many auxiliary vacuum lines as you can, so that they are not part of the test. The line to the reservoir that feeds axle and heater and cruise is one. Brake reservoir is another, if you're not going to drive it for the test, and if possible the feeds to Egr and crankcase vent. Leave the one for MAP, though.
 
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