My friend has a 99 XJ8 that sat for a year and a half after it stopped running. They were in a tough spot after a job loss and after having a new child they couldn't afford the new car payment anymore so I told them I would see about their Jag. I'll admit Im an Import guy. I specialize in NSX's/S2000's and any other Honda/Acura, but I will work on anything. I narrowed the problem with the XJ down to a bad fuel pump. I drained all the old gas out and replaced the Fuel pump, filter and plugs and after dumping oil into each cylinder to build compression I finally got it to start. But When I drove the car it falls on its face after about 10% throttle. I keep getting a Random misfire code and System too lean codes and then it goes into restrictive performance and I barely made it home. So far I have gotten the following codes out of the car:
P0300
P0307-(I switched coils from 6 and 7 to see if it changes cylinders)
P1314
P1316
P0443
P1000
P0171
P0174


I also checked for vacuum leaks and found none.
Right now Im guessing its some kind of cam sensor or a MAF.


Any Jag gurus with experience care to chime in and help me help this family in need?

Hard reset, start the car and let it idle for a minute or two. See if that changes things.

Worry about the misfire and P0443. See which come back...

I think you do have a bad vacuum leak and you did not find it. your description at 10% throttle indicates a vacuum leak. Plug in a scanner and look at the short term fuel trims at idle and under throttle

Have the secondary cam chain tensioners been changed ? Why was it parked for a year and a half ?

Idle Bank 1




2500 RPM Bank 1




Idle Bank 2




2500 RPM Bank 2




MAF and TPS at Idle



unsure about replacement of that. It only sat because they didn't know what happened to cause it to stop running one day. Here are pictures of the results of the data stream while at idle and 2500ish rpm's.

STFT do not look too crazy and they are not at maximum correction. at 2500 rpm do they remain steady or do they head towards 0? While watching the STFT you can also spray MAF cleaner or carb cleaner all around the intake system, throttle body and breather hoses and look for the readings to jump.


I had the P0171 and P0174 codes (but none of the others you have) and it turned out to be an air leak in the supercharger by-pass hoses. I could not see or hear the leak but found it when I sprayed the MAF cleaner


Also, if you have not cleared the codes yet you may want to clear them and see if they all come back

Trims are fairly meaningless if you have such as misfire (commonly bad coil) or EVAP-type fault like P0443. Look at trims after fixing (if there's any point i.e. things don't work right and trims are a suspect)...

What are the Areas I should check more thorough for a vacuum leak?

The intake tubes and hoses from the MAF to the throttle body. The throttle body, the partial load breathers, and the EGR valve

JimmyL and I had a couple suggestions- have you tried them?

I did the hard reset with the battery and an "idle too high" code came up. I think it was p0205. Not sure car did the same thing if not worse. More then 5-10% throttle and car falls on its face and almost dies and bucks really hard. I couldn't find a vacuum leak anywhere...

Try a tech who knows these cars.