4200 Coupe Throttle Sticking

[AlfaMail]

My 2002 4200 manual has a niggling issue. When in normal driving the engine revs will not die off when throttle is released. I find myself using the brake pedal to slow the engine and the car down. If I dip the clutch the revs whip up to 2500 to 3500 RPM and stay there for some time before dying off to idle. If I keep the clutch up and the car in a high gear and use the footbrake to slow the car the revs do die a lot quicker. I have tried a good 2nd hand throttle potentiometer and good 2nd hand throttle body and there is no difference at all to the problem. I have tried to "re-set" the system by
switching battery off via boot switch for 20 minutes / switch back on and re-set alarm / entering car & closing door / switching all systems off / switching on ignition & turning radio off / start car not having touched pedals / let it idle for ten minutes / test drive. Tried this a couple of times and no difference at all.
I'm thinking that there may be an air leak after the throttle body ?, those small bore plastic pipes ( 3 or 4 of them ) that are all over the inlet plenumb chamber ....... could one of those be broken off and causing this issue ?. Is my re-set procedure coorect ?. By the way, I have removed the throttle body from hoses to look at the butterfly valve and left cables on and when pressing the throttle the valve opens and closes immediately like there is no problem ??. HELP

 

[CatmanV2]

Someone may know what this is exactly but I *think* you might need a code reader.

My Ultraguage, and I guess many of the app, will give an absolute throttle opening reading, which may be helpful to eliminate the throttle staying open even though the pedal has been released (although it does rather sound like your test has done that already)

Good luck
C

 

[Contigo]

It is one of two things. Either a failing throttle body (sticking further round than the 7 degree open position for idle) or a faulty Bosch Pedal Potentiometer. I've never heard of a 4200 TB failing so yours could well be the first!

 

[Contigo]

Throttle reset procedure from another forum:

The correct procedure is as follows:
Open the boot, turn off the battery isolator switch for 30 seconds plus (30-40), turn back on, shut the boot, reset the alarm which will bleep, open the drivers door, get in shut the door and , making sure you do not touch any foot pedals, turn off the aircon and any thing else that might drain power, wait for the interior light to go off, turn on the ignition, and try to turn off the Sat Nav and radio as quickly as possible. Leave the ignition on for 30 seconds plus, during which time you will hear all sorts of wirring noises and then start the engine. Leave to run for about 10 mins without touching any pedals, until up to working temperature, and the fans have cut in (checks they are working), and job done. You can do this one time after another, which as Aussie will confirm had better results, depending on your initial problem.