My 1.8 Focus has had a rough idle for a while now, it seems it wants to stall, but then it revs itself a little to stop it from stalling and repeats over and over, if that makes sence.
I have just today fitted my 2.0 port and polished head with piper cams and vernier pulleys, along with a new inlet manifold and throttle body, cam belts and tensioners, aux belt and tensioners, oil change and filter and thermostat, so near enough a full top end rebuild.
I know the cams will make the idle a bit rougher, but when i 1st start it, its idles nicely for 20-30 seconds...then it starts to go rough.
Im thinking and have read it could be faulty mass airflow sensor or idle controll valve, and to check vacuum hoses and change fuel filter.
The idle controll valve was new with the inlet manifold, so its not that.
Any ideas pleaseeeee help!
Thanks
Joe

 

Probably the coil pack.

 

Funny you mensioned that as i just realised this started around the time i replaced it last year and done it ever since....a mate had a new coilpack he didnt need and gave it to me, so i fitted it as it was new, maybe its faulty.
I still have my old one, will fit and try tomorrow, one thing i dont get though if its coilpack, wouldnt i have loss of power too and even one plug not firing?
Thanks
Joe

 

Even though it was 11 i just went and quickly changed my coilpack over as it was so easy to quickly change and try....still seemed to do it unfortunately.
Think ill try mass airflow sensor next and check the vacuum hoses.
Thanks again
Joe