I've got a strange misfire situation

[jodykprice]

This is a long story, but that's what makes it so disturbing. My 2002 ZX2 has been missing off and on for 3 months, but hardly enough to notice. Recently, it became more noticable and I got a cylinder 2 misfire code. I then changed the plugs and wires and fuel filter with no results. A week later, it started to miss on cylinder 1 and 2, and REALLY run badly. I slapped in a new coil pack and it seemed to be perfect. I was wrong...by the next morning it was back to the little cylinder 2 misfire. I've since run fuel injector cleaner and HEET through the system. It completely stopped the misfire for 2 days when the temperature here rose into the 60's, but came right back when the highs dropped into the 30's and 40's again. Most days the miss is very intermittent and subtle, others not so. It seems to be worse when the weather is cold, if that is even possible. It always starts up easily and idles fine. The miss occurs most often while accelerating and sometimes while cruising.
Any advice would be greatly appreciated...this problem is getting more mysterious by the minute. Thanks everyone!
-Jody

[91 bird]

just did some timing belt work on a 2000. it also had a missfire problem. the wire for plug #4 was loose. i squeezed the metal clamp inside with vise-grips just a little. it snapped hard on the plug but did the trick to end the missfire.

[Scrapper]

that more sounds like head casket leaking if you put new plugs in it and it still runs bad. a plug can miss after putting a load on it like taking off fast it misses under power. so try a compresion test also have you been using antifrezze? but it could also be a valve.

[jodykprice]

Thanks for the info, 91 Bird and Scrapper. I just added coolant to the empty reservoir when I did the plugs and wires two weeks ago, and that's the first time I've added coolant since I bought the car new in 2003. It's never run hot though. I'll try a compression test. Could the head gasket be leaky or a valve be faulty when the miss comes and goes? On the average day on the 15 minute drive home from work it might hesitate/miss 10-15 times, other days once or twice, and others not at all!

[Davescort97]

Look for a vacuum leak close to cylinder 1 and 2. It will run fine while it's cold , but will miss after it has warmed up which makes the mixture leaner. Also, your year zx2 has been plagued with holes and cracks in the rubber inlet to the throttle body. The ignition work you have done on it seems to make up for the vacuum leak which is making it run lean. Also, the injector cleaner would make it run richer compensating for a too-lean mixture.
Check all the rubber hoses coming off of the intake plenum. Replace the PCV valve. Check the PCV hose where it runs into the intake plenum. The elbow has been known to crack. Somewhere your engine is getting too much air making a too lean mixture.

[jodykprice]

Thanks for the post Davescort97. I did notice that the elbow leading from the PCV valve back to the intake was cracked. I did a quicky repair with electrical tape, but didn't notice any results. Aside from that one elbow, the rest of the duct-work looks and feels good. Also, the engine has not thrown a lean code, only misfires. My brother is a mechanic, (lives out of state though), and thinks that if it was a vaccuum leak it would idle poorly and if the engine was running too lean or rich the computer would code for that. He is totally stumped, as I am. He was a Honda Master Tech and now works for Kia, so he is no Ford master. His last words of advice for me yesterday were, "Take it to the Ford dealership.." You guys seem to be my last hope.....

[nicks99zx2]

Hello all, I know its been a couple years sence the last post to this topic. But my 99 zx2 is having the same problem. I just rolled 100k on it. I've done the timeing belt, plugs, wires fuel pump(entire assembly) fuel filter. Presher tested the cylinders and injectors all is good except the intermittent skip or hiccup as I call it. Did you ever figure it out anyone have any new advice?