cycling idle

[Cypher007]

i have an early 850 2.5 20v 1992, which uses the Bosch LH-3.2 system. i find the car has a tendancy to cycle its idle speed up and down by about 60 rpm, it also seems to misfire at about 2500 rpm to the extent you can hear a small break in the exhaust note every second or so. i also find the car quite thirsty, any ideas?

p.s. checked all the on board diagnostics no error codes found.

[sheerwater]

A million and one things!!!!. Sounds however like a plug breaking down or one of the HT ignition leads deciding to pack up. If you have a multimeter its fairly easy to check the OHMS in the leads to see if they have any difference. Plugs are fairly cheap so.....! On idling check for leaks or tiny splits on the rubber air hoses and vacuum tubes. Worth taking off the constant idle valve and flushing it out in case there is crud there. Are the injectors clean and not playing a poor pattern. Hope this helps a bit. Cheers Nigel

[Cypher007]

i connected a car foot pump to the fuel rail at the end where theres a valve i got about 35 psi at idle increasing to about 38 psi when i reved the enegine. i have also checked the inlet mainfold vacuum, at the little multipoint tree, and it goes from about 20.5hg down to 19.5hg following the idle speed cycles.