Restricted Performance  1999 XK8

The Dreaded Restricted Performance And The Road it Took Me Down

Began receiving a Restricted Performance (RP) amber light off and on for a few days. Thinking that the K&N air filter I elected to recondition it, by the way, came with the car when we purchased it. Cleaned the filter and still had the RP off and on but the frequency had changed. It appeared less often. When the RP was not on, the car ran great. No hesitation at any time with the exception of when RP appeared it would not go over 3000rpm. I checked and did not have any OBD codes.
June 24, 2008 - After much discussion with friends and online I elected to replace the K&N filter and install the factory filter.

July 7, 2008 - 400mi trip and RP did not show up when driving at speeds 55-65+. It did show up on warm-up after the car had been sitting for a period of time and had a chance to cool down. No OBD codes!

July 13, 2008 - I cleaned the Throttle Body and the Mass Air Flow Sensor and replaced the plugs. I also checked the Breather Stub and found it clean as a whistle. Also checked wiring and all the connectors and fuses. It seemed that the car ran better but still RP. I did notice that I had no consistency in the frequency of the RP occurrences. In fact I began keeping track of what I was doing when it occurred. At this time I elected to install BG 44K to the gas thinking that it could be a clogged injector.

July 26, 2008 - On a 400mi trip RP did not appear at speeds of 55-65+. However, it did when the engine was cool. At this time I elected to replace the Mass Air Flow Sensor. I elected to replace it because 1) I thought the oil from the K&N filter may have caused it to provide an inaccurate reading. 2) By popular belief that this could be the cause.

July 27, 2008 - On a 200mi trip and the RP came off and on the entire trip of speed 55-65+. This time the engine light came on. At last a fault code! Great! Checked OBD codes and found P0328 Knock Sensor. I was out of town and elected to reset the OBD codes to see if it reoccurred. It did NOT! For this reason, along with others, felt it was a false reading.

August 2, 2008 - Much discussion on line, other mechanics and the good old standby people who had no idea what I was talking about. I made the decision to give it to the experts. I had checked all I could check or what I knew how to check at the time. I went to the archives at three Jag chat rooms to give me direction. Found none!

August 6, 2008 - Turned the car over to the Jaguar Dealership and told them the problem and gave them a list of what I did and what took place. I told them specifically about the Knock Sensor P0328 and detail discussion on the suspected problem.

I was told that a portion of the wiring harness in the front of the car was damaged and had to be repaired. The code on the wire was for the Knock Sensor. They also checked the sensor and it showed normal readings. They did, however, find an internal electrical fault in Throttle Body and verified the fault. Had the Throttle body replaced. We thought we had it. I was told that the fuel trims were a little high so we performed a smoke test and found no leaks. We were told to drive the car and the fuel trims should level out. So we drove again.

August 8, 2008 - A 400mi trip no RP on the trip at speeds 55-65+. Still had a problem when cool and low speeds. How long does it take for the fuel trims to level out?

August 13, 2008 - Took the car to the dealership to find the problem. Found an intermittent Knock Sensor that produced a Check Eng light one time. They felt it may have failed when the wiring harness was damaged. Had it replaced and at the present time it seems to be running great and no RP.

Throughout the entire time I began working on the car the RP was appearing inconsistently and improving at times leading me to believe that I was making progress. At times it would not appear when I thought it would and other times far to often. The car ran great and had a lot of spunk. When I suggested the Knock Sensor to the Jag Dealership they told me it could be the problem and would check into it but it was highly unlikely. When talking to them about the Knock Sensor I asked if my trying to accelerate with the RP light on could have caused the knock sensor to sense the false reading. I was told that when the car goes into a RP is will retard the timing and the sensor was designed not to read that kind of knocking. Well it was a learning experience for me. Hate to say it but I was on the right track when I began looking for a loose or poor connection just did not go far enough.

I want to thank everyone for their input and helping me get the problem resolved. I also hope this will help others in their quest to resolve a problem like this.