Re: '89 80 - miss and idle instability problem

["Anthony K.B. Chan" <chan@seattleu.edu>]

Is there a crankcase ventilation pipe in the 4 cylinders model? I am not 
familiar with the 4 cylinders, I had an 85' 5ks and now a 92' 100 V6.
My 5ks has similar but not exact problem. The problem was traced to the 2 
piece crankcase ventilation pipe. The actual pipe from the crankcase is 
metal but it is very short, it is then connected to a plastic pipe that 
goes to the idle stabilizer. The two pipes are connected together by a 
piece of rubber hose that are clamped to each of these two pipes. Over time 
the rubber hose melted partially and created any air leak. The engine 
missed as if it was an ignition problem. I even replaced all the plugs as 
well as the coil and the coil wire and finally traced the problem to the 
crankcase ventilation pipe. It was a $5 fix, I did went to the dealer to 
but a section of the rubber hose, it's $5 for a foot(it has 1/8" think 
wall and even has part number on it), only need two inches of it. 

Good luck,

Anthony Chan, First Hill, Seattle, WA, USA.
chan@seattleu.edu
92' 100 V6 Tornado Red.

On Tue, 7 Jan 1997, Bryan Lally wrote:

> Date: Tue, 07 Jan 1997 22:25:44 -0700
> From: Bryan Lally <bryan@mst.lanl.gov>
> To: quattro@coimbra.ans.net
> Subject: '89 80 - miss and idle instability problem
> 
> My Audi goes vroom at idle.  No, this is a bad thing!  It also misses.
> Anyone want to play a remote diagnosis game?  Here are the details to
> date.
> 
> Car: 1989 Audi 80.  2.0l 4 cylinder.  Front wheel drive, not a
> quattro.  72,000 well-taken-care-of miles.  KE-Motronic fuel injection
> (the mechanical fuel distributor, continuous injection setup with a
> Motronic computer unit).  The car was running fine until about 1 month
> ago, when it started this behavior suddenly.  As we started to
> investigate, the car suffered from the cappucino incident (failed
> coolant pressure cap), which was not connected to the current problem,
> and has been fixed.  I realize that the offering to the Audi gods for
> the pressure cap may well have been insufficient.
> 
> The short story:
> 
> The car exhibits 3 symptoms.  All happen somewhat sporadically -
> sometimes 2 seconds apart, sometimes 2 minutes.  The symptoms are
> 
> 	1) vroom at idle,
> 	2) miss, most noticeable under load, but seems to occur at any
> 	   speed or load
> 	3) voltage blip at test point used to read motronic fault
> 	   codes.
> 
> The "vroom" (1) is a momentary increase in RPM from idle by 3-400 rpm.
> The idle goes back to normal immediately.  It is caused by the idle
> stabilizer responding to it's control signal - i.e., the stabilizer
> works, and the computer is generating the signal to make it go vroom.
> Why is it generating this signal is the big question.
> 
> The miss is a short miss, but seems fairly complete, like spark
> disappeared for a short period.  Not a light stumble.
> 
> The voltage at the motronic test points is normally 1.5v (engine
> running), or 12v (engine not running, key either on or off).  During
> the "blip" the needle swings to ~5v.  Of course, the actual spike
> could be higher (it's probably 12v), but it is short, and the needle
> doesn't react that quickly.  The correlation factor for the voltage
> spike and the vroom/miss is 1.0 - they _always_ happen together.
> 
> The long story:
> 
> The idle vroom is annoying, and a bit of a safety hazard in parking
> lots.  The miss is bad enough that it must be fixed.  We've been over
> everything we can think of, and have come up blank.  Any ideas before
> I take it in to Mr. Dealer?  Or, just want to play along and predict
> what Mr. Dealer is going to find?  I hate to admit defeat on this one.
> Here's what we've looked at.
> 
> Alternator - we disconnected the alternator and ran the car on the
> battery, in case the diodes or voltage regulator were causing voltage
> spikes that were confusing the computer.  Nope.  Rule out faulty
> alternator/regulator.  We also looked at the voltage across the
> battery terminals, and saw no spikes.
> 
> O2 sensor - we disconnected the O2 sensor, and ran it open loop.
> Nope.  Rule out faulty O2 sensor and exhaust manifold leaks.
> 
> Intake leaks - we searched for intake leaks, false air, etc.  We found
> none.  All the hoses look to be in excellent shape.
> 
> Slightly temperature dependent? - the symptoms don't seem to appear
> immediately after a cold start; it takes about 1.5 miles for anything
> to happen.  The symptoms do occur immediately on a warm start.
> 
> Water temperature sensor/switch - we have complete gone over the
> temperature sensor and switch, measuring, testing, etc.  We were
> really interested in this, as the problem seems to be _slightly_
> temperature dependent, and since we got temperature sensor fault codes
> from the computer.  Finally, we determined that the temperature
> sensor/switch should have a value of about 200 ohms when the engine is
> fully warm.  So we put a 200 ohm resistor in the wiring harness, to
> simulate a warm and perfect temperature signal.  Nope.  Rule out the
> temperature sensor/switch.
> 
> Idle stabilizer - other than the vroom, the idle is perfect.  If we
> let the clutch out slowly, feeding in no throttle, the idle stabilizer
> will keep the idle speed up and we can drive away.  The stabilizer has
> been cleaned.  If the stabilizer is disconnected (with the engine
> warm), the vroom will (of course) go away.  The miss and voltage spike
> remain, and the car idles nearly perfectly.  Rule out idle stabilizer.
> 
> It was suggested that since the Motronic computer is near the lower
> heater duct in the front passenger foot area, that leaving the heater
> off might prolong how long the problem takes to commence.  No, this
> doesn't happen.
> 
> What to do next and possible theories:
> 
> Take car (and wallet) to the dealer.  Make a proper offering.
> 
> Check power input to computer, at the computer connector.  If this
> voltage is intermittent, the computer will be constantly rebooting.
> 
> Check temperature sensor value at the computer connector, to look for
> faults in the wiring harness.  Not very likely, as the problem occurs
> with the temperature sensors disconnected completely in the engine
> compartment.  This test says that the temperature wire is not going
> open, as we created an open and the fault still occurred.  It is
> perhaps slightly possible that this signal is intermittently getting
> shorted to ground.  But it has no correlation with driving over bumps,
> etc.  It will happen idling in the garage, not moving.
> 
> Open up the computer unit, and spray "cold" spray on the components
> while they are operating and see if the problem can be made to
> disappear or get worse.  Of course, squirting stuff on the operating
> computer is risky and may end up with having to perform the following
> item.
> 
> Replace the computer - expensive, if this isn't the problem.
> Expensive, if it _is_ the problem.  Anyone know an approximate price
> for one of these?
> 
> Resolder connections on computer.  I've looked at the boards, and
> there is not much that can be done in there.  This isn't hand-soldered
> hardware, although I've heard of someone doing this on a K-Jetronic
> setup.  A screwup results in the previous item.
> 
> Because of the abruptness of the voltage spike, and the similar
> performance at all speeds/loads, I have concentrated on electrical
> problems.  It just doesn't seem to me that fuel flow is the problem
> here.  Let me know if this is a bad conclusion.
> 
> As always, thanks for any advice.
> 
> 
> 	- Bryan
> 
> '94 BMW K75S		_red_
> '94 Honda XR250L	with extra needles and thread
> '89 Audi 80		I think I can, I think I can ...
>