a dreaded uneven idle

[antz]

what would cause my dads 855 T5 to drop in idle then rise then make a weird tick noise and do the same thing again?

completely standard engine, nothing added from the factory.

any ideas?

[t5 pete]

If its doing it all the time it could be a air leak and the engine is hunting or it could be the idle controll valve also look at all pipe work adn check the intercooler hoses for leaks

[nobananas]

I'd say air leak too. Maybe just into one cylinder, like an inlet manifold gasket or an injector seal. Get a can of something like easy start or even brake cleaner, something that if drawn in to the engine will effect it's running and spray it around any joints, hoses vac pipes etc and listen for a change in engine tone.

[antz]

cheers guys. Its only started doing it tonight so will have a good look round it tomorrow!

[antz]

it was the air con clutch apparently? Or something like that.... My dad moved the dial back to AUTO and it solved it. How odd.

[Volvostorm]

It was the air-con compressor kicking in, they do take alot of power from the engine, hear it a lot of small engined cars

[96T5Andy]

from previous experience when mine kept cutting in and out it like this it was when the amount of whatever-it-is in the system had almost all leaked out and it was turned on. Maybe time to get the aircon topped up.