Thanks for the responses.

How could a too-lean adjustment cause the problem?

This is an intriguing possibility, cause i did have a mechanic
(different than the shop that installed the engine) adjust the
mixture after it was obviously too rich (smelled gassy & poor mileage).

On May 14, 2006, at 1:57 PM, -------------------- wrote:

> Your problem is cause by one of three things:
> 1 lean a fuel adjustmnet, witch is unlikely
> 2 timming to far advanced
> 3 or as you say a intake valve out of adj.  witch will
> also cause a bad idle.
>
>
> Michael Diehr wrote:
>
>> 85 with a newly rebuilt engine.   Seems to run fine at speed, but at
>> idle is behaving very weirdly.  Been fiddling with the idle adjuster
>> screw, and can't seem to find a setting that lets it idle when cold,
>> w/o surging upon deceleration at 1500 rpm when warm.  Pretty sure the
>> throttle closed switch is correctly adjusted, timing is good, etc.
>>
>> The latest thing that has me worried is a bizare "clunk/zap" sound
>> coming from the airbox.   It happens intermittently when the idle is
>> dropping below 900.  Dissappears completely if you goose the throttle
>> to get it above 900rpm.    As near as I can tell, the sound is caused
>> by a "pop" that is reverberating through the throttle body, AFM, and
>> airbox.  If you put your hand on it you can feel it happening.
>> This is a brand new rebuild engine, and this is a sound that I've
>> never heard on a vanagon before.
>>
>> Could this be caused by a broken/stuck/misadjusted intake valve?  (so
>> that when the cylinder fires, pressure is going back up the intake
>> manifold?)  If so, why would it only happen when the engine is
>> lugging at idle (say, 750 rpm or so?)
>>
>