[V8] rough idle (update)

dsaad at icehouse.net dsaad at icehouse.net
Wed May 26 15:02:44 EDT 2004

For the ISV, if it is mechanically working - ie smooth turning with no rough
spots, try putting a ohm meter on the connector pins (ISV off the car obviously)
and rotate the shaft while watching the meter. If there is a dead spot you MIGHT
see it this way.

For the MAF, K&N filters can cause problems with these if they are over oiled.
The MAF is easy to remove and clean - but it is also fragile and expensive. Take
it out and inspect. To clean try spray brake cleaner - and possibly a Q-tip to
very carefully clean the wires.

You can also monitor the MAF output voltage with a volt meter. The exact
"correct" voltage is hard to determine but this is basically a standard Bosch
MAF electrically (physically it is way different). I found a testing procedure
and pinouts (off the net somewhere) for a Chevy Camero that worked for me. It
also used a Bosch MAF. The manual also has some procedures for testing. It might
give a normal range for idle output voltages. I think the big thing to look for
is a fairly constant voltage from a constant RPM.


Quoting QuickAudi at aol.com:

> Well, I just got sick of my rough idle the other day, so I took every part of
> the air intake apart that I could and cleaned them all, even though they were
> pretty spotless.  I also serviced the K&N.  These two seemed to help a
> little, as the idle is not as rough as it used to be, but it is still far
> from purring.  That makes me think that the culprit is an air measuring
> device.  Could a MAF make the idle rough?  Idle control valve is working fine
> and clean, but could it be gone mechanically/electrically?  I also noticed a
> few other holes with hoses running to them; are there other sensors that I
> should know about?
> Also, something else that might help.  Before I had the low rough idle, I had
> a high idle.  It would not be present until about 2 minutes after starting
> the car, then, just like someone threw a switch, it started to idle high.  I
> think changing the OXS helped out with that problem, but oddly threw it the
> other way.  I probably should run a VAG-COM to see what it is saying now.
> Anyone near Nashville, TN?  I'll be in Birmingham, AL this weekend if that
> helps.
> One more thing: before the throttle, the air is "chambered", for lack of a
> better word, into 3 chambers.  Two go to the throttle butterflies, the other
> goes to a hose.  What is that hose?  It goes right next to the right bank of
> cylinders, and it had a little oil...
> Joel
> '90 V8q (getting headliner replaced tomorrow!!)
> '86 5kcstq
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