1988 Audi 90 - Air-Fuel Mixture Problem

[Kent McLean]

schief53562 at peoplepc.com wrote:
 > Our 1988 Audi 90 is a 5 cylinder 5-speed with 198,000 miles.
...
 > So . . . the last recommendation is to replace the fuel pressure
 > regulator.  I declined for now because they wanted $500 for the part.

Before you throw more money at the problem (at people who
seem to be just guessing at the cause), I'd try pulling
diagnostic codes:

http://www.sjmautotechnik.com/trouble_shooting/10naecu.htm

At the risk of repeating myself, without the codes, I'd also
check 3 things:

1) The O2 sensor. When was it last replaced?
2) The ISV. It may just need a good cleaning.
3) The MFTS (multi-function temp. sensor, if the 90 has one;
    I'm assuming it does) is also problematic - a frequent
    source of failure that causes funky problems.

A Google search of the Audifans website will tell you more about
each of these.  The ISV is also covered in the KnowledgeBase.

--
Kent McLean
'94 100 S Avant, "Moody"
'89 200 TQ, "Bad Puppy" up in smoke