I know this is a common topic on the forum but I seem to have come up with a new version; and of course, I don't get any code reading when I connect my code reader to my 2002 XK8. This has happened to me a couple of times. The first time I was cruising I-40 through the Mohave Desert at 70 mph (A/C on). The check engine light came on and the restricted performance signal would go off and on depending on whether we were climbing or on level terrain. The amber check engine light remained on constantly. When I got home I connected my code reader and got no code, so I erased the memory to see if it would occur again. I went a couple of months of mostly city driving and the problem didn't occur again. Then again, on the highway at around 70 mph (A/C going) it happened again. Still no code reading and the restricted performance signal is off un less I hit the highway. I've checked the obivous things like the air intake and vaccum lines and don't find any problems.

Anyone have any ideas on this before I apply for TARP funds to have the dealer track it down and probably try to sell me something I don't need.

 

Get some CRC brand Mass Air Flow Sensor cleaner and clean the MAFS. Keep your scanner in the car and plug it in if you see the RP warning again. P0172/ P0174 means buy a new MAFS. That's the most likely scenario, not an absolute.

 

Hey thanks,
I'll give that a try.

 

this happened to me and was intermitant coil failure.

 

I too had a coil pac failure, It was in # 6 not that that means anything but I would not think it is a pack because they usually only fail when they get hot and expand. But when they are cool as on first start everything is normal. But the coil should throw a code when it is hot and expanded. That was the case on mine. it took the dealer several attempts to get this code but it only came up when the car was hot not just operating temp hot. But operational temp plus some drive time, like you did in the desert.

If you clean your sensor you can remove the two screws that hold it in place. You do not need to take apart the whole airbox.

 

JagTech,
Well I tried the CRC MAFS Cleaner and still get the messages. I hooked up the code reader and yesterday my wife took a day trip with instructions to try for a code reading if the messages showed up. She got the messages twice but neither time was she able to get the reader to pick up a code. Here's the interesting part that I would like your opinion on whether or not it may play into the problem. Yesteray after my wife got home and the car sat for about 10 min, I went out to see if by chance I could get any code readings. I turned the ignition to position two and without starting the car the engine fan, or fans, came on. I turned the ignition off and took the keys out but the fans continued to run. I started the engine, and let it run for about 30 seconds and turned it off and the fans went off. The temp. guage was registering normal temperature. I'm wondering if the fans or some fan control module may be the culprit in the ck eng. / RP situation since the messages only happen when cruising at hwy speed on hot days (yesterday it was 102 degrees).
What do you think?
clayray73

 

Not enough info to anwer that question, if the fans only ran for a short time than I would consider that as normal. Engines heat soak after they are shut down, the fans might not be running when you get home...once the coolant has stopped circulating, it is expected that the temperature will be higher ten minutes later.

 

You may try cleaning the throttle body as well. These were expensive little failures.