Hey guys - my 99 XK8 with 98K miles has been throwing codes for the last couple of months (occasional driver), and at times also goes into "restricted performance" mode. That said, I thought it might be a MAF sensor, so I replaced it with another one, and have the same issues. I pulled the codes this last time and I had 4 of them (the same ones keep showing up) PO1637, PO172, PO175 and P1000. One interesting thing is, the "Restricted Performance" message will come on at times, and will limit how you can drive the car, but then as you keep driving, it goes away and then you can drive it without any restrictions. I don't know when the plugs were changed last, so I'm doing that next. Any other thoughts? Thanks in advance -

 

P1000 Means that SRT's are not complete (system readyness tests) Dont worry about that its just a side effect of the other codes.
P1637 is a CAN code. A concern in the CAN circuit between ABS/TCCM and ECM. This one can be tricky. The most common cause for a can concern is a poor ground. An open or short in wiring or control unit failure also can cause this. "occasional driver" in your description would lead me to start by taking a close look under the hood. Check for the presence of rat droppings and chewed wires. If not present check all engine grounds and if possible loosen and retighten them. Alot of the time this is all that is needed. Reset (clear) codes and test drive to see if this code comes back. This code can cause tcs/abs and poor idle concerns.
P0172, and P0175 indicate banks #1 and #2 are rich. Any input sensor that can affect both banks could cause this as well as a restricted air filter. If you have a scanner, check short and long term fuel trim. If they arefarther away than 15 points from "0" you are experinceing the concern now. If they are at or near "0" you are not. Check short term fuel trim for both banks at idle and at 2000rpm. If the concern is only present at idle, It very likely is due to the CAN code and you must address that first. Also if the fuel trim is close to "0" at this time get a base reading from the short term fule trim, and long term fuel trims on both banks. Also get reradings from your; MAP,MAS,CTS,IAT,And CTS. Get all of these readings at idle and at 2000rpms. They will be very useful in diagnosing and confirming the repair,

Let us know what you find and we will be able to help you further.

 

Not often we see both banks rich. Its usually lean. A few more days and some more views by our engine gurus will give you some more places to look. Be patient...and good luck.

 

Thank you for the replies, and I've printed off Brian's feedback, which I will give to my mechanic-friend who will help me troubleshoot. Any more help/ideas would be great!

 

well, its at the top, so maybe get a few more looks