1994 306 1.8i SR Sedan with Magneti Marelli 8P ECU.
Whilst curing a pinking problem (see separate post) I decided to cure the slightly hunting idle and ease of stalling when coming off idle to drive away that has developed gradually over the past year.
Everything pointed to the idle control valve getting gummy, so I undid the two torx screws and withdrew it from the throttle body.
The valve itself (a rod with a chamfered end) was indeed covered in a gummy residue that looked like mixing pencil graphite with old engine oil, so I wiped it dry, carefully cleaned it with Gunk, dried it, cleaned the rod's mating chamfered face in the throttle body with a clean and dry cloth, then put it back together and reconnected the wiring plug.
A dead easy job, so imagine my surprise when the engine then refused to idle once warm with cold start circuits then closed.
After trial and error I found that I could pull the actuating rod in and out of the body, and when I did so it sounded like I was over driving a gear train inside. This surprised me as I would expect a simple solenoid (a coil with nothing mechanical beyond a damping spring). If I pushed the rod all the way 'home' the car then idled at 3200RPM(!) and gradually dropped to 1500 RPM over 30 seconds. It then vroom-vroomed between 1500 and 1800 RPM on a half second cycle for as long as I let it before switching off.
Anyway, the idle control valve is clearly kernackered and was failing anyway (see first paragraph) so I shall buy another, but I'm still interested in learning what has happened as a result of simple cleaning. Haynes makes no mention of any special precautions being necessary.
TVM.
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Unless I'm very much mistaken, the idle control valve is a stepper motor not just a simple "on/off" solenoid. Otherwise accurate positioning of the valve would be impossible!
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It's a good idea to switch the ignition on and then off while you have the Idle Speed Stepper Motor out (connected of course).
Just make sure that you put your thumb over the plunger to prevent it coming out while you do it. Then re-fit it and start the engine again....
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Thanks for the comments.
I ended up buying a new one though as the original refused to work properly after cleaning, no matter what I did. This included leaving the battery disconnected for half an hour so that the ECU lost any learned settings and allowing the motor to reset as described above. Using the same techniques the new one worked right away and not only has idle hunting been banished but so too has the ease of stalling when pulling away; I can now drive in to our garage completely 'right foot free' with the stepper motor correctly countering the drop of engine speed as a result of climbing a small concrete ridge with clutch slipped at much less than walking speed.
Though not surprised, I didn't thing £95.44 incl VAT was exactly cheap though for a few pence worth of components, no matter that it did have to be transported, stocked, etc.
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