I have a 1996 XJS with the AJ16 engine. Over the 13 years that I've owned, and daily driven this car I've had an uncommon, but repeating pattern of idle issues.

Maybe twice a year, maybe a little less, after acting as expected, at startup, the engine decides it wants to stick to 1,100RPM for way longer than it usually does at startup. I've extended the wait time, expecting the car to eventually warm up and return to it's normal 700RPM idle as it gets warmed up, but it doesn't seem to want to do that. I'll put it in gear, and sure enough, it will pull the car as if I have my foot on the gas.

I know this is something that others have complained about. My LTFTs were at -3.1%, so the engine was being fueled properly (enough). I have a PDU at home, so I was going to charge the battery and do a TPS reset, which I've successfully used to solve problems like these in the past. It works 100% of the time.

This time, however, when I got home, with the engine still hot and running, I stuck my hand under the throttle body and unplugged the TPS. The car's idle twitched a little, as it went into closed loop, and then I plugged it back in after about 10 seconds. This has solved the idle high idle problem. The next day, I started my car and had no issues with the idle. So far, the problem has not come back.

While I don't believe this will fix more common idle issues, typically occurring when throttle bodies are cleaned, or other service is done to the engine, I do believe that this may cure the change in idle when NO work has been performed on the engine. Or... maybe my car is an outlier and has something else going on. In any case, I thought I would share this with other AJ16 engine drivers to see if anyone else has any luck with this cure?

I will add that I have replaced all three wires with SXL type wire feeding the TPS (which was replaced with a new one a while ago, so while it might be 7 years old, it's not 27) from the ECU all the way to the TPS itself, including new terminal sockets and pins inserted into the harnesses, so there's no chance of any wiring shorts or issues with the conductors.