Strange running problem - help!

[tvart]

Car has started miss firing and sounds to be running a little odd. Its most noticeable on tickover, where the engine seems to hunt for the tockover rpm. It is ok for a couple of seconds, then it sound different, then its ok again and so on... i am also getting some backfiring at times. Power doesnt seem very down. A little while ago i found the vac advance unit hanging off, so i put it back on and all was fine, now its not quite right again. Ideas? Lambda probes, ECU etc...?

Is it possible to plug in a fault code finder? Anyone know a good RV8 garage in Derby?

[nf319]

have you tried cleaning the stepper motor? had a similar problem with mine last week, cleaned the stepper and gave the inlet side of the plenum a good clean, solved the hunting problem straight away. its easy to clean, just unplug it, unscrew it from the carb and clean it off with some methylated or whiet spirits.

[GreenV8S]

Was the vac advance module definitely hooked up to the base plate when you refitted it? If it had become disconnected you could end up with semi-random ignition timing which might lead to symptoms like that, as well as potentially blowing your engine to bits if it winds full advance in under full power.

[tvart]

yeah i made sure it was hooked up. It was loose for a little while though, but seems ok enough (no nasty noises etc)

I have cleaned the Stepper in the past, maybe its time to do it again.

Cheers guys

[tvart]

no, the stepper motor clean has not worked...

Its missing the odd beat and backfiring more... i guess the unburnt fuel in the exhuast when is missing... its nothing extreme, but a bit anoying. Seems to be most obvious at 2500rpm...

anyone any more ideas?

[tvart]

also forgot to mention that the car really coughs and needs to clear its throught when i start it up in the morning... more so if its very cold.

[george 500]

Mine was doing that last week, was caused by the air intake hose coming loose from the plenum. Just check that its sealed properly all the way round and that there are no obvious leaks.