Hi,

I recently visited my tuner for a checkover and a power run but I am a bit confused about my CO on idle. It was quite low when I took it in so he upped it to about 3.5 I think but after every run on the rollers it was going back down to about 1.5 without us adjusting anything He said it was because I cleaned out all the combustion chambers when I did the headgasket change so it needs to build up the carbon again, does this sound right ? if not, what would cause my CO to change by itself ?

cheers, Duncan

 

No its not, all you did there was drop the compression ratio very very slightly...

It depends what car your talking about, but il place a net on it being a small air leak with Bosch Ke Jetronic, like the diptick seal or the filler cap, cam cover gasket or sump seals a favourite...

 

yes its a s2 erst, you say it could be an airleak but how would that lower the fueling once we had manually turned it up on the metering head Could it be anything else ?

cheers, Duncan

 

Because with a low vacuum reading the metering flap has no stability and will not return to eaxctly the same metering position twice after being subjected to any leverage.

It is VERY dependant on teh correct needle displacement and that requires a stable and repeatable vacuum.

 

so its just a matter of searching for the air leak and fixing it yes ?

........could a small air leak like the above cause the car to nearly stall when I dip the clutch at junctions ? (it will idle fine though )

Duncan

 

Yes it will do EXACTLY that. 100%

To be honest, thats often caused by a suspect dump valve piston seat so if you have one, remove it.

 

ok cheers stu, I'll get looking