Ok all, I'm jumping right in. Have a 97 XJ6L with P0 300, 1313, 1314, 1138, 1157 codes and idled about 1500 rpm. I know that those are random misfire, emminent cat damage banks 1 and 2, rich and lean. Took it to a shop and he wanted to put in 3000 worth of coils off the bat. As I understand P0 300 is not a specific cylinder, just that generally everything misfiring. Basically I know only 3 things can cause that, something messing up the fuel, something messing up the air, or something messing up the ignition so I picked it up and took it home. All plugs have exact same coloring, so to me that rules out cylinder specific issues. Took to another shop, had pressure test/leakdown. Faired well except 2 cylinders indicated could use valve job. 160 psi across the board but leakdown on 2 cylinders was a little weak. This shop suggested $1500 valve job, $3000 coils, and $550 IAC. Picked the car back up . Ok now the 3rd shop, fixed the high idle with TPS recalculation, smoke test revealed no intake leaks, recommended new coils and all would be well. Picked the car back up because I can do the coils myself in 15 minutes.

Here's what all I have done so far. 6 new coils, new fuel pressure regulator, new fuel pump, new TPS, new MAF, cleaned TB, changed fuel filter 3 times, new plugs 3 times (white electrode indicating lean), new EGR, cleared codes several times and did hard reboot (which by the way didnt clear anything).

Car seems to run pretty good cold in open loop, starts its cutting out in closed loop when warmed up. Messes up the most on slight load (maintaing speed on slight grade), cuts out and misses big time, doesnt always throw immediate code after clear. If i play with the throttle when it starts missing it comes out of it and returns to missing. It's like it falls flat until I give it accelerator.

Any idears?

 

Ok, it's going back to shop in the morning. Jag parts are too expensive to just throw parts at it thru process of elimination, even though I went the logical steps, but I don't know what else to try . Unfortunately the shops want to throw parts at it too, plus make me pay labor. I'll let y'all know tomorrow.

 

FIXED!! WOOHOO! It seems the previous owner had put all new 02 sensors in and had swapped the upstream and downstream plugs when they hooked them up. That would do it lol. I never would have dreamed to check that. Runs beautifully now and no codes. Oh well, pretty much everything on my engine new now so I should be good for a while.