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Old 04-08-2003, 07:32 AM
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Join Date: Mar 2003
Posts: 64
Throttle Body Questions - W201 16 Valve


I removed the air flow meter on my 190 16V as the potentiometer has died. Looking at the throttle body, the plate appears to be sticking. There looks like a idle screw to the RHS of the throttle body but I'm not sure if that's what it is.

At the moment, the throttle plate is closing completely shut and takes a little bit of force to open with the linkage, it "snaps" open - I imagine the operation should be completely smooth? It looks like there is a slight groove worn in the throttle body. I suppose I have to replace this as well?

Finally where should the "idle screw" be set to? The plate closes completely on my car at the moment. Should it be slightly open? There are two tiny holes machined into the body I guess for vacumn takeoff, should the plate be below these holes and completely shut, or slightly open like a carburettor? Is there some sort of calibration procedure? I can't find it on the CD Rom.

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Old 04-08-2003, 09:58 AM
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Join Date: Jul 2001
Location: SoCal
Posts: 1,303
I would not expect a 'groove' in a throttle body, but a slight 'ledge' would be a normal part of the machining, and allows as complete an airflow shutoff as possible. The butterfly should not move past the ledge. Even though no fuel passes this way on first pass, vapors do, and so it is normal for a varnish to build up. That should be thoroughly cleaned off before you make any judgements about the smoothness of the throttle action.

I don't know the correct setting of the adjustment screw, but I would leave it where it is as a first course of action.

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Old 04-08-2003, 01:30 PM
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Join Date: Mar 2003
Posts: 64
Thanks Steve.

Whats funny about it in my eyes is the throttle plate is fully closed with the plate completely sealed against the wall of the throttle body. In other words the travel of the plate is not stopped by what looks like a throttle stop/idle screw. There is about 3mm space. I would have thought that the idle screw at least had the job of stopping the travel of the plate just a tiny bit before the the plate was fully closed, or at least to provide some respite to the throttle body wall from the plate due to the tension of the return spring.

Thinking about it a bit more, I guess the throttle plate is designed to be fully closed during idle. The idling is handled by the idle regulator through a totally different air/fuel circuit.

Will leave the throttle body as it is unless I hear otherwise, it was pretty gummed up so a good clean should have helped somewhat. Still thinking the screw/stop should be relieving the pressure of that spring... hmmmmmmm!

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