1.8 eratic idle
 

my 75 1.8 is now running but it starts fine but if i hit the gas peddle the rpm goes to 2500 and wont come down ... it only does this after it has been running for 5 min or so ( after aux air valve shuts off )

i am replacing all the vacume lines tommarrow if any body else has an idea of what to check so far i have checked the following :

1 throttle sticking .... no
2 idle screw ... no i can screw it all the way in and it keeps running
3 mixture screw ... no
4 vaccume leaks ... working on it
5 flapper sticking ... dont think so
6 cold start valve still squirting ... nope unpluged it

TIA


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scott thacher
75 1.8 running at last
75 under rust
(fine german rust)

Hello

Check the cold start bypass valve by pressing the hose togehter.

Grüsse

Check your Decel Valve. It's over on the right side of the engine bay. Haynes has a procedure to test it. It may be opening but not closing.

Check your timing. If it "sticks" such that the timing is advanced, the idle will be too high.

Check for anywhere else that air could be going from before the throttle body to after the throttle body.

--DD

well i thought of by passing the aux air valve ... was going to do that tonight

and dave i never woudl have thought of the decel valve but that is why you are the 1.8 god ( sorry to make you blush )


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scott thacher
75 1.8 running at last
75 under rust
(fine german rust)

I was having the same problem with my 75 1.8 so what I did is unhook the vacume line to the decel valve and plugged the line. Now I don't have that problem anymore and the engine drops to idle alot quicker, like a carbureated car. So far I have noticed no ill effects but if anybody knows of some problems with this procedure please post here.

The decel valve lessens the lean condition when the throttle is closed, shutting off the fuel supply, and the rpm are still high. Its purpose is to reduce NOx (Oxides of Nitrogen), the byproduct of a lean hot combustion. Plus your rpms will drop a bit more in between shifts.

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Chris
75 914 2.0L