Okay, I have a 1987 audi quattro 4000s, I just got this car recently
and i figure i should give it a once over, It runs fine, theres a
small problem with the idle though, but, I cannot seem to locate an
aircleaner anywhere? I took off my intake boot and just found a plate
that can be pushed down.
Am i looking in the wrong place?
If anyone could explaine to me where the aircleaner is it would be
The plate you pressed on is the Air flow metering device (similar to a
MAF in an electronic injection system). You will find the Air filter in
the black box just under it.
OTOH, you idle problem is probably not the air filter. More likely
suspects are a non functioning ISV (idle stabilization valve) that mixes
air at idle to manage idle speed. They can go bad, be dirty or failing
to operated because the triggering information to the ECU is missing.
The trigger is a micro switch on the throttle body that you can ohm out
in a three pin connector behind the throttle body. There will be three
contacts (one ground and one for closed throttle and the other for WOT
when you have your foot on the ON button to disable the AC). When you
release the linkage you should see one of the contacts completed. This
will tell the ECU to instruct the ISV to begin modulating idle air
volume ... idle speed.
If that is good then suspect the ISV itself and remove and clean with
alcohol and blow dry. This device is a variable solenoid that can be
tested with a 9V battery. If bad replace with a known good one.
There are a number of other things that can cause idle problems but most
likely among them is a vacuum leak. Check all hoses and especially the
waffle looking rubber between the air filter / air flow plate and the
Sometimes a vacuum leak is due to a sticking decel valve which you will
probably find (but be unable to reach) in the passenger fender behind
the air box. If you test this and it seems to be the problem just
disconnect it and plug the line going to it.
The fuel filter is not likely to be the cause as it exhibits problems
more when pulling under load or up a hill.
Let me know if that is TMI.
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