Volkswagen: Fast Idle on a 79 Vw Van Fuel Injection, mass air flow sensor, air flow sensor

Question
Ron,
I have recently purchased 79 VW Van (westfalia) that was a California van.  The problem is when the engine has warmed up the idle speed is around 1200 rpm.  The air bypass screw is turned in all the way but that is as low as the idle gets.  When the engine is cold the idle speed is about 1050 rpms.  Let me give you some history about what I know about the motor.  When I first got the van the motor was running too rich.  I was told to disconnect the oxygen sensor.  It did lean it out a bit.  I also turned the CO adjusting screw on top of the mass air flow sensor counter clock wise about 2 full turns which has leaned it out a bit more.  Currently I think that it is running about right in terms of not being too rich anymore.  The catalytic converter has been gutted.  I am getting around 25 miles per gallon on the highway.  I have tested all the components of the fuel injection system electrically.  The aux. air regulator seems to test out OK.  The Decel valve has the smallest vacuum line disconnected and plugged.  When I hooked it up properly, the van would take a long time to idle back down properly, so I disconnected it and blocked it off again.  My VW manual gives me two tests to check if the decel valve is working properly.  One test the decel valve passes and it failed the other test.  Do you think my decel valve could be giving me my fast idle or do I have other issues?  Thanks for your time.

Roland

Answer
Hi Roland,

It sounds like you have a very small vacuum leak, causing this condition.  They are the hardest to find, as they are not massive enough to cause the bus to stumble or stall.

Check around the air flow sensor, and also check the timing on the bus.  

If you timing is incorrect, it will idle high.

Thanks,

Ron