I have a 4 hour drive on Friday, so I'm hoping for good news... :-)

My XJ8 has been starting and running great. It has about 110,000 miles on it. Today, however, as I was getting ready to leave work, I started the car, and the engine was shaking, sputtering, losing power...acting as if it was starving for fuel and power (the dash lights were dimming at the same rate the engine was losing power). I shut it off and started it again - it did the same thing and the "Stability System Failure" message came up. I shut it off. I've suspected that the battery or charging system has caused some problems in the past (nothing with the engine), so I decided to disconnect the negative for about 5 minutes, reconnect, and try again. Same engine activity, but this time the "restricted performance" message came up. I let it sputter and shake for 20 seconds or so, and suddenly it started running ok.

Since the restricted performance message was still on, I decided to shut off the car and start it again. Everything is acting fine now. Drove it home (only about a 15 minute drive). This has never happened before, and I'm mostly concerned about the possibility of a tensioner problem. I don't know enough to know whether or not it could run fine after a tensioner breaks. I'm hoping it's something else.

Though I really don't believe it's something I did, by strange coincidence, I had done a handful of maintenance tasks to the car 2 days ago. Since I'm looking for ideas as to what the problem might be, and whether I should be concerned about taking my trip on Friday, here are the things I did to the car on Saturday:

- I changed the oil and oil filter. I refilled it with 5w30, which was not the same weight as it had previously, but it seems that was the suggested weight.
- I checked the air filter. It was clean.
- I charged the air conditioning.
- I disconnected the battery while I removed both driver side door panels (the front to replace fasteners, the rear to look for any obvious electrical issues that would prevent the seat memory buttons from working)
- I had the battery disconnected for about 2 hours.
- I made several 2 to 20 minute drives with no problems, including my 15 minute drive to work this morning.

Though I haven't driven it anywhere since I got home, I have started it a few times and it has not exhibited any problem.

Any thoughts, ideas, or suggestions would be greatly appreciated!

 

Have the battery load tested to eliminate that possibility. A failing fuel pump could cause those symptoms, but make sure the battery is fully charged. A failing tensioner could cause roughness on startup, but you would also hear the rattle then.

 

It does not appear to be mechanical. A failing tensioner does not correct itself, it only gets worse and leads to engine failure. It is in the electronics and there should have been some engine codes. Plug in an OBDII reader to see if it registered any fault codes and go from there. My wife's 99XJ8L with 106,000 miles on it will every now and then start with a rough idle and then will smooth out soon after. The intermittent electronic controls are the hardest to find and correct without throwing tons of new parts on it.

 

It could be that some electric contact failed, one of those things that are impossible to diagnose but easy to blame.
I had somewhat similar problem on my ford long ago, car started running rough and eventually died and would not start. Disconnecting engine computer/module harness and connecting it back few times solved the problem.