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Poor Idling


Beesty
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Hi all

new to this forum this this might seem a bit cheeky my faithful old 1993 3.9i disco is playing up it idles very fast when u start it and is very slow to drop the revs when u put it in park. its starts brillently when its cold put when its warm its a pig idles badley for a short while then sorts its self out and the ticks over fast again, just wondered if anybody had come across this before and had a fewpointers.

thanks

phil

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Welcome to the forum! A lot of people's first post is when something goes wrong - strange that ;)

Sounds to me like the bypass air valve - aka stepper motor, aka idle control valve. It sits right at the back of the plenum chamber and has wires connected to it. It can be unplugged , removed and cleaned with electrical contact cleaner although in my case this gave only temporary respite.

Things to watch out for: Don't lost the big washer and don't over-tighten (only 20NM)

If that doesn't help then there is a really good diagnostic guide which you can find from here

Hope this helps

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Welcome to the forum! A lot of people's first post is when something goes wrong - strange that ;)

Sounds to me like the bypass air valve - aka stepper motor, aka idle control valve. It sits right at the back of the plenum chamber and has wires connected to it. It can be unplugged , removed and cleaned with electrical contact cleaner although in my case this gave only temporary respite.

Things to watch out for: Don't lost the big washer and don't over-tighten (only 20NM)

If that doesn't help then there is a really good diagnostic guide which you can find from here

Hope this helps

thanks for that threesheds where do i find that plenum chamber thing i'm afraid i'm not very switched on to engines!

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thanks for that threesheds where do i find that plenum chamber thing i'm afraid i'm not very switched on to engines!

Probably best to get a book... But:

the pelnum chamber is the chamber on the very top of the engine - the air from the air filter goes into it and then out through the inlet tracts, past the fuel injectors to the cylinders. So if you follow the top of the engine back then the stepper motor is between this box thing and the bulkhead. It is controlled by the ECU (Electronic Cntrol Unit) and opens or closes to control the idle speed. When and why it opens is quite complex, but if it is sticking then the symptoms could be similar to those you describe.

p.s. If you fill in your profile (particularly where you are) then you may well find that there is somebody local who will be willing to come and help you out...

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