I have a 1988 XJ with 166k miles. It idles ok when in park but once I put it in gear it idles rough and even stalls sometimes at stop lights. I ran Seafoam through everything and that didn’t work, any ideas? I was told to replace the TPS but hate to spend $60 and have that not be the problem.
Thanks, John
Had a similar problem on a late 90s XJ .. ... using two different tps sensors one was a new aftermarket the other a used OEM ... both produced intermittent problems until one, can't remember which one, was adjusted ...
basically what i did was loosen one hold-down screw and remove the other ... test probes are placed on the back side of the connector with everything connected ... swivel the tps sensor until it falls within a certain voltage range ... then tighten ... it took several tries until problems vanished ... you may need a manual and/or specific instructions for the voltages, resistances as well as other testing procedures .
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* it is sometimes better to first consult an automotive service manual for a specific vehicle ... to determine symptoms, basic tests, resistances, voltages, etc.
.. from memory ... off-hand ... ... the tps also provides data to the transmission via the TCM ... can effect shifting functions, which might be related to idling, rpms, .. etc.
.... Once had a stalling problem related to the CPS ... found wires became burnt and were grounding on the exhaust ... if you need to replace sensors such as the cps and others ... make sure wires are routed correctly or problems may occur ....
here is one link to basic tps diagnostic and testing
http://autorepair.about.com/library/faqs/bl232i.htm
Here are some more symptoms and test procedure posted on another jeep xj forum for a 95 Xj .... may or may not help to diagnose idling problem ... (tried to link it but the link kept coming up broken)
TPS
Physical Symptoms:
The engine loses power and is stalling. The engine will idle, but may die as soon as you press the gas pedal. When driving, it seems as if all power is gone. Sometimes speed maxes out around 25 mph, and it feels as if the transmission is failed or isn't shifting properly, if at all. You can be going 25mph down the road at 5,000 RPM's. If you quickly jump on the gas you might be able to get the transmission to shift into second, but it won’t shift properly by itself. Shifting manually, the transmission goes through all the gears.
TEST
You should have 5 volts going into the TPS. At idle, TPS output voltage must be greater than 200 millivolts. At wide open throttle (WOT), TPS output voltage must be less than 4.8 volts.. The best is to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. One of the other wires should show .26V (or so). The other wire will be the ground and should show no voltage. Move the throttle and look for smooth meter response up to the 4.49 at WOT.
Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.
atriot:
