Bought a 2003 XJ8 with 16,000 miles (verified). The car was sitting in a garage and not driven for 5 years (due to age of owner). Changed all fluids, tires, filters, a few rubber-related parts. The car passed inspection. The problem is engine and warning lights and limp mode popping in after about 20 miles of driving. OBD indicating fault codes for throttle body, and for ignition coils and spark plugs in cylinders 1 and 3. Throttle body and sensor cleaned and now I'm inclined to replace all plugs and coils. Can anyone think of an argument against doing so? Additional info: the car was purchased by an elderly woman in Santa Monica, CA and primarily driven short distances on secondary roads in her neighborhood for 15 years before being garaged. I know the daughters and they do not think their mother (now deceased) ever drove on the car on a highway. Stores and social functions. Back to the sparks and coils... thoughts and opinions greatly appreciated. As well as manufacturer recommendations for sparks and coils (leaning towards NGK. Also, I'm not a mechanic but have been under the hood and car before including changing the air suspension on my wife's 2004 XJ8 to the Billstein shocks and coils kit (which I prerfer to the air suspension). I''ve posted on this car before, back in January or February. Had to focus on another project (the kind that brings in money so I can feed this cat), but now I''m back into getting this pristine lady on the road. Thank you for taking the time to read this post.

 

I'd move the coils around on the car (taking note of which is which) then see if the fault follows the coils. If not then do the same with the plugs to narrow down what the actual fault is.

 

I would pull the coils out and just look down inside to make sure no condensation exists on the spark plugs. If none exits, do what was suggested by Hooli and move the coils around. Label the tops of the coils with the original hole they came out of before you move them. 1-4 on passenger side and 5-8 on the drivers side front to back. I would clean out the MAF sensor as another possibility. Run super unleaded fuel, monitor the coolant temperature and drive it hard on the highway to blow out all that crap.

 

Bad gasoline that old could be a cause.

 

I think a good fuel system cleaner is in order (SeaFoam or equivalent); clean the throttle bore and plate again; MAF too, again; have a tech change the fuel filter; a new load of good gas. And as A2B noted, get it up to speed -- 4000 or more RPM to blow out the gunk . . . check for new codes. Plugs are easy to do; just takes time (an electric screwdriver with the right 7 or 8mm socket saves a lot of wrenching); examine the plugs . . . I like NGK platinum; but Denso good too.

Sounds like a steal, particularly if the interior and finish are pristine. . .

 

Thanks for the suggestions. It is in pristine condition, and time will tell if this Jag is a steal.

 

NGK for spark plugs you can inspect the coil while engine running. Rock auto sells aftermarket for probably 20$ per piece they work fine I have couple of them

 

Electronics can degrade over time even with low miles.

If it was my car, I would at least put a new set of plugs in it although they might just need to be cleaned or subjected to a spirited Italian tune-up. A new set of plugs won’t set you back much. Those steel plugs have been in those aluminum heads for a long time now so go easy getting them out. The dissimilar metals react with each other which causes corrosion on the threads. Put a dab of anti-seize on the threads of the new ones. Many shops will skip that step so you may need to ask them to do it.

The spark plug oil seals in the cam covers also fail over time and allow oil to leak into the plug wells. That can also cause your symptoms. You’ll see if that’s an issue if there is oil on the plug wire on the coil pack when you remove it.

As mentioned earlier here, you can move coils around to identify bad ones. I believe OEM are Denso. I replaced all of them on my ‘01 VDP when I got it with NGK. Either is probably fine.

My car had the same issues as yours when I bought it with 38k miles. New plugs, coil packs and cam cover seals fixed it and she has been old reliable since then.

 

I always use Iridium plugs in my cars as they last a long time. NGK or Denso brands. At this moment one car has NGK the other Denso. Both run well.

I'd start with the plugs and label and move the coils as mentioned by Addicted. If you have a bad coil, the car will throw a code to let you know which one is not firing correctly.

 

Researching causes (wiring, bad plug)... the wiring seems okay, looks brand new. But the OBD didn't flash this until recently, after the car had been driven a half dozen times and about 200 miles. I replaced all the plugs (NGK). I did find oil - on the plugs on the passenger side. Which is making me wonder about a cracked gasket, given the age (22 years since build) of the car.

 

Is this a "FOUND IT, EVERYBODY QUIT LOOKING" answer to the post?

 

 

This is purely for entertainment purposes for those who have walked this path before me... I'll run it tomorrow and see what the next challenge is.