A little history first. I just purchased a 1999 XK8 with only 58,200+ miles on it. The previous owner had it for just shy of 7 years and only averaged 1861 miles a year in that period!

On driving it back home from West Palm Beach, a 325+ mile trip mostly on the Interstate. I registered a "restricted performance" & "check engine" light coming on after about 100 miles of 70-80 mph driving. I had just completed about a 20 minute rest stop at one of Florida's service plazas and was accelerating back into traffic and settling down for another couple hundred miles when it lit up.

It was the AMBER light not the RED light warning so there appeared to be no actual restriction that I could feel. Of course at 70-80 it never registers more then 2500 RPM's so I didn't experience any 3000 RPM limiting going on. The car still ran like a well oiled machine and I cleared the "restricted performance" message but could not clear the "check engine' warning.

I continued north for about another 175 miles when I exited the interstate at Gainesville, Fl., and stopped at a store for something cold to drink and a leg stretch. This was at about 12:30 AM so it was cooler than it had been earlier. Anyway as I left the station the "restricted" light came on again with no noticeable change in performance so I cleared it again only to have it come back on almost immediately. Cleared it once more and continued on the 50 or so miles to home with no further problems. At one or two points on that leg I passed some light traffic and know that not only did I exceed 3000 RPM's but also was approaching the 100 mph neighborhood as well so there wasn't much restriction was there.

Here's my current operating theory and I would like those who've experienced something similar and have found the fix to chime in. The OBD II scanner that I use (OBDwiz V2) in conjunction with my ASUS Netbook pulled just 2 codes; the 0171 & 0174 listed above. Those codes indicate a lean condition on the right and left bank.. The JTIS gives several possible trouble spots ranging from a restricted air filter, restricted fuel filter, low fuel pump pressure, and onto more difficult to troubleshoot electrical problems.

I think the problem probably lies with the injectors or within the throttle body as the mileage driven by the previous owner would indicate long periods when the fuel system would have been the victim of fuel evaporation in all of the injectors as well as the throttle body. Those periods would could have led to an accumulation of various residues such as sulfur that would restrict the fuel flow especially at higher speeds. A problem exacerbated by any potential 'heat soak' condition due to the car sitting for a few minutes between higher speed runs.

I have given the MAFS a through cleaning with a cleaner specific for the job and I am replacing the air filter as a matter of normal maintenance anyway. I also have a spare Jag fuel filter handy that is for a 4.2 XJ8 but I'm betting it's the same for the XK8 as well that I might install since I have it handy. I also dumped a 'fuel injector' cleaner into the tank along with my next fuel fill but haven't driven far enough to see what effect, if any, that would have.

Since those minimal 'fixes' I have had occasion to really wail on it both in normal and sport mode with hard acceleration up to the ton without any recurrence of the "restricted" light but the "check engine" light did reappear with the same 2 code #'s.

I have both the 1999 shop manual and the JTIS II installed on a couple of my computers and having owned the XJ8 for about 2 years I'm familiar with their uses. What I'd like is to hear from any others who may have encountered a similar problem and what, if anything, they may have done or found that 'fixed' the problem.

 

Could be a significant vacuum leak, couldn't it?

Try to get a look at your long-term fuel trims...the Torque App for Android phones is used by many forum members (including me), and can read various ECM data points in addition to reading codes.

You might just have a significant vacuum leak between the MAFS and the manifold (since it's throwing codes for both the right and left banks).


.

 

I just recovered from a similar problem and will second what The Coupe said. I'm thinking a vacuum leak. It will run fine at highway speeds, and the codes may actually clear after 15 or 20 minutes at highway speed, but you will likely find that the codes come back during city driving and it may not respond well to the throttle. If this is what you're seeing, then it is a significant vacuum leak.


Mark

 

This time I ate the bear, which is unusual when you're dealing with Jaguar's isn't it.

My problem with the CEL and restricted performance message got to where it was coming on within a minute or two every time I went to drive the car. There was NO noticeable difference in performance despite the dire warnings contained in the DTC portion of the JTIS II program so I was pretty much at a loss as to just what was happening. For once following the path of the simplest explanation (also usually the cheapest solution) seems to have paid off. I replaced the air filter with a K&N as a matter of normal maintenance and took the MAFS out and gave it a through cleaning with the appropriate cleaner. It took 7-8 solid sprays to get the gunk off the deeply recessed wires buried up inside the sensor. Before doing that I had cleared the 2 codes (P0171 & P0174) as well as the CEL.

I took the car out for the suggested test drive which calls for driving at a speed of 40 mph for 1-3 minutes. I actually drove for a much longer period of time and eventually at a higher speed and the CEL and warning messages and lights DID NOT RETURN.

I'm keeping my fingers crossed as I really don't want to have to get into removing and cleaning the injectors, fuel filter, etc.

 

The single most common problem is an air link in the air filter to throttle body area with the first thing to look for is breaks in the plastic accordion section of the duct. It sits directly above the exhaust manifold for a few years of baking.

 

Like Tom said the most common problem is a an air leak. See if this procedure helps

Link http://www.jagrepair.com/images/Auto...otos/P0171.pdf

 

I had the exact same problem with my wife's '99. When I bought it , same codes. repaired the intake duct with electrical tape, cleaned MAF and throttle body and all was well for a few years. Then problem returned, usually after a 20-30 mile drive. Replaced duct with new, cleaned MAF and T/B, no change. Swapped MAF with my 2000 XJ8, and problem has been gone for about six months now. The XJ8 was totaled from an accident, so its a parts car now. Hope this is as simple for your problem.

 

My problem was on my Jaguar S-Type, 3.0L 2000 with 144,500 miles. I got the Codes 0171 and 0174. As my car has always been spotless (I keep the engine very clean as well) and as all the hoses look like new, I was convinced that I had bigger problems than a vacuum leak....however I DID have a vacuum leak. Here the details:

I built my own smoker with a plastic nuts container (see attachment). Blew air into it at low pressure with my shop vac. Made smoke with a small smoke pen (used by contractors to detect airflow in houses). Worked well.

Then I noted smoke coming from the rear of the engine (between engine and passenger compartment). On investigation I found a rubber grommet which was totally disintegrated. The pipe is attached on the front end at the throttle body, passes over the engine block to the rear end, through a 90degree bend, then fits onto a larger pipe facing vertically down behind the engine block (note: I am not an expert, just a retired businessman).

So I replaced the rubber grommet (I had to make my own, as I could not get something to match from local spares shops). The grommet has an approx 10mm opening on one end and about a 20mm diameter opening on the other.

I have attached a few pics to show where I found my vacuum leak. Again I did not believe that any of my hoses were in bad condition, but was proven wrong.

 

Your idea and it's application will be very helpful in the future and I hope the pictures remain available for those who find your post.

In my case the codes were the result of a very dirty MAF Sensor located in the air intake duct between the air filter box and the throttle body and after a thorough cleaning they went away.

Unfortunately a car that has seen little such maintenance over the past 7 years as it was essentially not being driven more then about 150 miles a month on average the check engine light becomes an almost weekly occurrence and reminds me of the game whack-a-mole since as soon as you cure one fault another one pops up.

Having fixed the P0171 & P0174 codes I am know trying to plan my approach to solving a recent P0455 code which indicates a fault in the EVAP system of varying levels of expense. My current operating hypothesis is that my recent interstate run of several hundred miles along with my efforts to clean the MAFS along with a couple of doses of injector cleaner have caused the EVAP system to become overloaded or otherwise saturated due to a faulty sensor or dump-valve system. That's most likely going to mean the removal of the left front tire (driver side) and the removal of the fender inner liner so I can get to and inspect the EVAP canister and its other components.

Life with the Jags is an ongoing adventure<G>

 

It's been stated on this forum for years that these cars hold up much better with fewer issues when they are driven regularly. Based upon 2.5 years of ownership with my wife's 2006 XK8 (and her taking the car from 36,000 miles at acquisition to nearly 82,000 miles now), I tend to agree....

 

The intake pipe 'bellows' had hardened, became brittle and developed leaks


Thought I'd share my 'fix' to a similar problem. (Only had bright pink duct tape) Was to be a temporary fix but its been holding for a few months now