Remedy High idle Speed - 1988 R Plate1.8 ts Alloy Top Engine.
There are a number of threads about this, but I am putting this up as it should come up under the most obvious search criteria for those with this problem. This applies to 1.8 TS engine with IAV on top of the throttle body and alloy top engine, not plastic. It may apply to others but that is the engine in mine so thats all I can speak about.
1) Disconnect lead from IAV which is a black box on top of the throttle body.
2) Release and unscrew the 2 star-drive bolts holding the IAV to the throttle body. Be careful you don't drop the washers down into the engine bay.
3) Take the IAV off and sqirt a shed load of carb cleaner into it and the housing on top of the throttle body.
4) Use a cotton bud or similar lint-free item to swab off the carbon deposits which believe me will be very obvious.
5) Allow to dry out then refit as reverse of the above.
6) GENTLY tap the rounded section on the right side of the IAV a few times to dislodge any sticking bits of carbon.
7) start her up and rev up and release a few times. You may get a few misfires as the carbon and other cr*p is blown through, but it should then settle down to idle at about 850RPM. If it doesnt, the IAV is probably shot and might need replacing.
Hope this assists, and thanks to all those who have posted various bits of advice about this elsewhere in these forums.