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Poor tickover and misfire

DaveB

DaveB

New member
After 3 months of faultless fun in the 944 and with a service due this month, the S2 has developed an annoying tickover problem and occasional misfire.

At tickover when hot (only) it hunts between 500-1000rpm.
Rev it at tick over and it picks up fine but when you take your foot off the gas, the revs drop very low and it starts hunting or just cuts out.
Occasionally will only start with no throttle - touch it and it just churns.
Very occasional misfire when cruising - one of those 'did that misfire or was I imagining it?' moments.

Under power it doesn't miss a beat.

Should I just wait for the 12K service and see what turns up?

Thoughts.


 
Possibly the idle control valve - the possible misfire wouldn't be down to that but the idle issue most certainly could be. A service wouldn't clean it as a matter of course though you could get it looked at then.

It's tricky to get out without removing the inlet manifold (but I've done it even with my 10 sausages for fingers), but once out some carb cleaner to break down the varnish inside can work wonders.
 
I would also consider the throttle position switch a suspect in this case. I had similar sounding problems that persisted after cleaning the idle control valve.

Confirmed to be the throttle position switch (black thing with a multi-plug connection on the end of the throttle body) by tapping the switch and wiggling the electrical connector whilst the engine was running - the idle returned to normal. In my case I cleaned the connector and refitted ensuring it was properly seated and I have had no repeat of this issue.

Phil

 
Good suggestion. I was also thinking about the air flow meter, but it tends to degrade over time rather than suddenly get dodgy.
 
Hi Dave,

Try removing the AFM (Air Flow Meter) connector and spraying it with contact cleaner. Then re-attach it making sure it is firmly connected.

Regards,
Andrew
 
Happens when hot - worst time for an ignition system. How old are the plugs/leads/dizzy cap? Check for arcing (bonnet up on a dark night, and watch to see if there are sparks. It can be helped by spraying the engine with a fine mist of water at the same time.)


Oli.
 
These symptoms are almost exactly what I had a few years ago. I took it to my specialist, he had a good look around, found nothing particularly amiss then hooked up the MOT AFR probe to the exhaust and realised that it was very lean at tickover. Was solved by re-setting the mixture settings and it has been perfect ever since - sits rock steady at idle, picks up smoothly and never missed a beat.

Definitely worth a check as well as all the other stuff that has been suggested.
 
A 12K service sorted the slight misfire (I'm guessing it was a dodgy plug), but it still had the hunting at idle problem. The easiest thing to check was the throttle position switch, so I tried that first. I cleaned all the connectors with switch cleaner, reconnected it and checked the position. Hey Presto! no more hunting.
 
Just put a multimeter on the terminals and checked when it closed at the end of the spindle travel. Bit of a guess, but it worked.
 
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