Evap system errors with misfiring Cyl 3
2002 Jeep Liberty 3.7L, auto, 70k miles, heretofore no problems at all other than a minor evap leak, apparently fixed with a new gas cap about two months ago.
Time to change the plugs, so I replaced the originals with Bosch Platinum iR Fusions. All was swell. Then, whilst traveling down the road, engine temp normal, accelerating, between 55-60 mph the SES came on, started flashing, and the vehicle started running like an unbalanced washing machine. Slowed down, went home, put the code reader on and found P0303.
Electrical connections looked good. Given the recent plug replacement, I thought perhaps I had gotten a bad one, so replaced #3 with another new one, and cleared the code. No joy. Same problem, same conditions. So I swapped coil packs with #1 and tried again. No joy. Same problem, same conditions, same cylinder.
Now, however, in addition to P0303, I had a major evap system leak code. I found that, with dry-rotted hose coming off the LDP and plugging into a tube going forward to the engine compartment. Also found a very loose hose from the canister. Replaced the rotted hose and pushed the other back in place, clamped it, cleared errors, and tried again. The engine was cold, and I was able to accelerate normally to about 70. Then the engine warmed up, and ... I still had the P0303, flashing SES, but now with a minor evap leak.
Now here is an interesting thing. If I accelerate very gently, or do not exceed that 55-60 range, I don't have any problems. And, if I do get the error, and the rough engine because of the misfire ... if I clear the error, the engine runs quite well until I cause the SES to trip. Which is coming first here, the chicken or the egg? Clearing the error 'fixes' the problem?
I'd appreciate any help with this one. TIA.