Please could someone shed some light on a issue that I cannot seem to cure.
I have a 1998 fully rebuilt, 1293cc Cooper sports pack with stage 3 head, 1.5 roller tip rockers, fuel pressure regulator, 52mm burlen metal throttle body, 3 branch manifold LCB, 3 inch fletcher exhaust and a k and n panel filter. Newly rebuilt gearbox with x pin diff and central oil pick up.
My issue is that the revs hang for a second or two on overrun. It is really annoying as when you dip the clutch the revs do not drop instantly, so it feels like you are slipping the clutch slightly.
Other than the above the car runs superbly with lots of power, no flat spots and very responsive.
The spark plugs are relatively new and are quite black and sooty, except for the electrode being grey.
The mini has been put on a snap on reader and only came up with the usual faults that are not applicable to the mini. (Ambient air temp, and another that I can’t remember but I think it was an oil related fault that is not applicable)
The throttle cable is new and not sticking.
The throttle body is new and is not sticking.
Throttle pedal has full movement and the spring is returning it fully.
I have fully cleaned the IAC valve and renewed the o rings on the IAC and the plastic housing that attaches to the throttle body.
I have checked for air leaks but cannot find any and the pipe work is quite new (less than 3k miles)
The only way I can I stop the revs hanging is to disconnect the IAC valve, then the car runs perfectly except you have to give it a couple of revs when starting from cold as I have now disabled this feature. I do not like the idea of making this a permanent feature so I would like to fix it without wasting money on items that do not fix it.
Please could someone advise if the Rev hang is normal with the MPI or if not, advise what else I could check to cure this.
Thanks very much Nick
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