Engine not correctly returning to idle

[jwrayth]

So after a week of running smooth I seem to have developed more problems! My engine starts properly from cold and settles on an idle of about 775 RPM with a very minute bit of hunting to start off. However, after some time running the idle begins to stick around 1500 rpm to 2000 rpm. If I manually depress the idle microswitch then my revs _sometimes_ drop back to the expected 775 RPM, however sometimes engaging the microswitch appears to do nothing.

It appears to only get worse the warmer the engine gets, to the point where engaging the microswitch does nothing to help the engine idle.

I assume I'll need to take the air filter assembly off to get a better look, but can anyone advise as to what the issue may be? Bad micro-switch or a bad grounding would be my inclination, but I'm not sure if there is something else obvious that I am unaware of...

[Guinney1971]

just as a thought, I've had a problem with Flopsy over the last year with it idling erractically
and often at around 2700rpm, but its not been all the time.

A bit of fiddling around found one of the multiplugs (one of the white ones) near the coil to
be abit loose - pulled it apart, cleaned the contacts up with a fibre pen (available from Maplin
and the like), tightened the pins up, and hey presto, fixed.

Funnily enough, I also had issues with my rear lights (as did 'Sorbet') prior to the MOT, and
that was down to the black multiplug in the same area on both cars.

[stunned_monkey]

I'd start there too. Sounds like en intermittent connection to the idlespeed thermistor - pins 9 & 11 on the black box. If the plug is showing open circuit, there's your culprit

[jwrayth]

Not to sound like a newbie (despite being one!), I just want to verify you are talking about connections to the Idle ECU?

[Guinney1971]

its the white plug next to the black plug in the coil area - it does go to the
idle ECU, cleaning the connections and making the connections tighter has
totally cured Flopsy's intermittent idling issues, and she's starting and driving
a hell of a lot better now.

[jwrayth]

That appears to have done the trick! Decided to clean all the contacts to be safe and put it all back together and now I'm getting a nice return to idle consistently.

Re-adjusted my idle microswitch screws as well now that the idle system appears to be working correctly so it's all playing nice!

On to my parking brake binnacle light next...

[Guinney1971]

nice one, it might be worth everyone checking the contacts on those plugs, they seem
to be responsible for all sorts of gremlins!

Glad you're sorted anyway