Re: ur-q air temp sensor

[Robert Houk - SMCC Bos Desktop Hardware <rdh@UrQ.East.Sun.COM>]

   I've a problem with my ur-q which started about six month ago and has slowly
   been getting worse. Symptoms are on startup after sitting overnight engine
   fires almost immediately (good) but if I press the gas pedal AT ALL it
   starts to die. It will remain at idle no problem but don't touch the gas!
   After idling for about 4-5 minutes it will then respond to the pedal but
   very poor on power and very rough - bad mis-firing which does not seem to be
   confined to any one cylinder. This applies throughout the whole rev range
   from idle to 6500rpm. Idle very lumpy when warm. So far I have replaced the
   fuel pump, both fuel filters, the fuel metering head, spark plugs, plug and
   coil wires, coil and have even gone as far as replacing the head gasket,

It's OK, it probably needed it anyway. . .

   head skimmed (2 thou), new valve guides, valve seats re-cut, and valve faces
   refnished. I threw in a new water pump, timing belt, alternator belt and PAS

BUG! Valve (and seat? not sure?) are "coated" (surface treated); refinishing
them destroys them (will wear very quickly).

   belt just for good luck. Even went as far as new studs, nuts, bolts, washers
   etc. for every joint that was opened! I have also had the fuel injectors
   tested and they are confirmed OK. I used new injector 'o' rings and Bako
   inserts when refitting injectors. I've tried a spare brain (MAC01) but no
   difference. Turbo comes in when it should, giving the extra boost expected
   but still with mis-fire. 
   Two things have been suggested to me:
   1. Warm-up regulator (fuel pressure regulator)
      With new fuel pump and filters fitted I'm reading 5.2 bar fuel pressure
   coming from the fuel tank. If memory serves me right (some time since I
   checked) I read 4.2 bar coming from warm-up regulator engine hot or cold.

Definite bug; don't have the charts here, but as I recall the pressure from
the regulator should drop off about 3bar (a lot, anyways, better than half
of max; again as I vaguely recall) as it warms up.

      Suggestion was the problem lies in the pressure from the reg. being too
   high resulting in the flap in air-flow meter not being able to rise when I
   press gas pedal....recommended replacing the reg.

Look at either O2 voltage or duty cycle on the frequency valve (does the
MAC-01 even support the freq valve?). O2 voltage should be oscillating
around 0.5V; lower is lean, higher is rich. Duty cycle should be oscillating
around 50% as the ECU reads the O2 voltage and tries to keep it at 0.5V
(higher duty cycle is ECU trying to enrichen the mixture; lower duty cycle
is trying to lean out the mixture). That should tell you a lot about what
the engine is doing, and what the ECU thinks the engine is doing . . .

   2. Air temp sensor (on inlet manifold)
      Suggestion here was that a dodgy sensor can cause poor running throughout
   rev    range.(I thought this sensor only had an effect when over 4000rpm).
      I've tested it using the procedure recommended in the Audi Introductory
   Service Training Information Manual (many long overdue thanks to Mike    of
   Bedford N.H. for sending me this invaluable book). Book says reading at
   room temp should be 13 - 33 ohms.....my reading 22ohms. I applied hot air
   from hairdryer - reading goes up to 26 ohms. Then I applied hot air from
   portable gas soldering iron (temp approx 300c) - reading only goes up to 32
   ohms. Still less than the book said for room temp! Can this be right?
      Does anyone know what reading I should be getting?

You're right on the money there. This is one of the ***STUPIDEST*** things
I've seen Audi do (although arguably not as stupid as feeding the 12ga circuit
with a 16ga tap off of the 10 ga circuit . . .) in the "electrics" arena!
The signal level of the air temp sensor varies from around 70mv (yes, that
is .070 Volts) cold to around 150mv hot. Wonder why the wires are soldered
to the sensor in the intake manifold . . . Idiots!

The book range of "13-33" is pathetically absurd. Don't have my notes
here, but 22 sounds about right for "ambient".

Symptoms of bad air temp would be engine cut-out at 4000rpm under boost,
and somewhat retarded timing otherwise, but not by an excessive amount
(you'd notice it as not quite as peppy as you thought it used to be, but
it's not a major "something's seriously wrong" type problem).

   Can anyone provide any hints on this problem? Mighty p%^&*d off at this
   stage and 880 Pounds (1200USD) out of pocket without solving problem. Wife
             ^^^^^^^^^^^^^^^^^^^^

You're just getting started . . .

   says either car goes or I go! Help!

Can I have which ever one you get rid of?

					-RDH