# Fuel mixture too rich when idle



## destinationelp (Jul 26, 2012)

Hello, I have owned many newer cabriolets/golfs/jettas. Recently I bought a "project" 1981 Rabbit convertible and I am having some problems with its idle mixture is too rich and engine smokes black. If I drive it around smoke goes away and if I return to idle it seems to be normal for about a minute or two at good idle RPMs then it goes back to black smoke and idling rough (until say I drive it around again). 

When the car starts with the smoking problem I also hear a whining noise from the fuel pump below but more importantly from the fuel distributor itself. The fuel distributor gets real loud. There is a leaky gasket on the exaust flange that goes from the header to the pipe down the car. I'm thinking maybe if I fix that and replace o2 it may work.. but I want to know what you guys know about fuel mixture too rich on idle only with that whining noise. 

Ive seen somewhere a bad cold start (leaky) valve will cause it to run too rich but not sure if that may cause a noise. I checked timing and I tried it a tdc 0 degrees but it is now about 5 degrees ahead (idle got a bit faster but still too rich). I will appreciate any help as I am under budget and dont want to buy parts I dont need.


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## ps2375 (Aug 13, 2003)

First thing to but is a Bently manual. Then to set idle mixture you'll need either a wideband sensor w/ gauge or an exhaust analyzer. Since it kinda sounds like you have a CIS-Lambda system, you will have noise from the fuel dist as that is the freq valve trying to work. You could disconnect that and set the mixture and things should be OK. If you still have a CAT, then you might want to gut it or get the system working properly as the reason for the O2 sensor ws to ensure the proper mixture for the CAT to operate.


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## EuroKid83 (Jan 26, 2005)

*Idle mixture adjustment*

You can adjust the idle mixture with a dwell meter or a digital multimeter that can read duty cycle. Here's a example.


















The hard part is going to be getting the engine to stay running long enough to get it up to operating temp. Once that's done adjust the idle mixture screw untill the needle on the dwell meter swings between 45 and 55 percent. If that doesn't solve the problem then you have a leaking cold start injector or some other fuel system problem that will require more in-depth diagnosis. Have you checked system and control fuel pressures yet?


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