My 2001 Focus 1600 Zetec petrol has developed an annoying issue with idling. It became 'lumpy' with an inconsistent idle speed, with the rev counter needle twitching around, sometimes jumping up to 1100 rpm, and occasionally settling at around 750 rpm. A few times, when dipping the clutch after a high speed run, the engine cut out altogether but restarted easily.
After the local mechanic tested it via the computer port and said there was nothing showing up, I was advised to replace the ISCV, which I thought was worth a shot for 45 quid for a genuine dealer part. After fitting (and disconnecting the battery for a while to force the ECU to 'relearn'), everything seemed great once I'd driven it for a few miles- steady, smooth idle and no alarming dips in idle speed when dipping the clutch. So I thought it was fixed- wrong!
After being parked up for a couple of days I took it out today and it's back to its old tricks, though not quite as bad. Drop the clutch and the idle drops to about 200rpm briefly, and when idling there's sometimes a rhythmic 'hunting' effect, which can be both heard and felt. Also, the idle speed will sometimes jump up to around 1000rpm for a few seconds for no apparent reason. It definitely feels better to drive, but obviously the idle problem needs rectifying.
Can anyone shed any light on other possible causes please? I read somewhere the throttle body can become contaminated and need cleaning, causing similar symptoms, but I don't want to randomly pull out parts and fiddle with them unnecessarily.
Thanks
Morse