My car is a 1997 XJ6L. This issue has been a bit random so far.. Some days the car will start and run fine, other days this is a big problem. I've been trying to feel out the problem and its generally been getting worse. Then yesterday the car ran perfectly, so now I'm puzzled.

This started a week ago. I drove about 45 minutes, then the car sat turned off in a parking lot for about two hours. When I came back, the car started fine, RPMs went up on the start, but rather than settling at idle, the RPMs dropped past the idle mark and went to the floor and the engine died. I started the car two or three more times with the same issue. I started revving the engine after the start to keep the RPMs from dropping. After a minute or so of this, the car seem to hold at idle, and I drove home 45 minutes without another issue. I should note that the car starts fine each time, and it seems to rev fine and smoothly when I give it gas.

The car ran fine for a few days of normal driving, then in the middle of last week, I drove about 30 minutes to work, the car sat in the parking lot for a few hours, then when I came out and started it, the same issue surfaced. This time it was a bit worse, however.. Once I was able to regain idle after a few restarts and revving the engine slightly, I put the car in Drive, pulled out, and as soon as I hit the brake to slow, the RPMs did not catch at the Drive idle mark, dropped to the floor and the engine died while I was driving out of the parking lot. This happened about three times before I was able to get to a safer spot to sit and let the car sit and idle for a while. Eventually, everything seemed to sort itself out and I was able to drive back home the 30 minutes without an issue... I should not that I always let the engine temp warm up to outside of the blue mark before putting the car in Drive and moving.

Three days ago the issue surfaced again, very similar to the first instance though, with the exception that a few times while the RPMs were dropping down to zero, the engine did seem to catch just before zero and the RPMs rose up to the idle mark again. The car sorted itself out by the time I put it in Drive and did not die while I was moving. I started thinking that I had filled up at a new, cheaper gas station the two previous times and maybe there was water in the gas. At this point I was below a quarter tank on the gas gauge, so I went to the autoparts store and put in some HEET to help remove any water in the tank. I drove for a few miles, then filled up the tank at a different station.

Two days ago was the worst so far. This was with the gas tank 3/4 full... I started the car at home a few hours after returning from a drive, and the RPMs went to the floor. I primed the fuel pump a few times by turning the key on and off a few times before starting, but when I started the engine, the RPMs fell back down to the floor. After a few starts, the car seemed to hold idle fine. I backed out of my driveway, coming to a full stop. Pulled to the end of my street and stopped, pulled out onto the street, but when coming to a stop at the first intersection, the RPMs went past idle and the engine died. This happened a few more times at the intersection before I was able to get it going and out of the way just by shifting it into park and driving to keep the RPMs up. When I pulled up to the next intersection, the car died again. I pulled the car to the side of the road, turned it off, then restarted the engine. The car seemed to hold at idle, so I let it sit for a few minutes. Then I drove off very cautiously. The car seemed to run fine and still held idle when slowing or stopping at intersections. I then completed my hour+ drive without any more issues. The car ran fine the rest of the day with periodic trips, and the car ran fine all day yesterday with more periodic trips.

I don't think its the battery because it seems to start fine every attempt. I don't think its bad gas or water in the tank because I put in some HEET, and the issue seems to occur regardless of gas level and fill location. I don't think its the alternator because the charge level shown on the dash seems OK, and its not fluctuating while driving.

I don't think its the fuel pump, because the car starts just fine hot or cold, and priming the pump a few times before starting didn't seem to help. The CEL is off and the engine isn't throwing any high level fault codes... It actually seems to run great otherwise..

Any ideas on what to look for next? Maybe there is something I am missing?

Thanks

 

replace the crank sensor, common problem for this description and Ive replaced mine 2 times since Ive owned it in 11 yrs