1988 Audi 90 - Air-Fuel Mixture Problem

[Ben Swann]

Clarification to Kents suggestions below:

1) Suspect this as the culprit

2) ISV not likely to cause a accel. hesitation problem.

3)  No MTFS - there is a dedicated Fuel Injection Thermo Sender which may be 
dual function for the temp guage as well.  this can definately be a problem, 
but usually would effect startup.

Again, good to know how to pull codes, but not as easy to do on this engine 
and not likely to reveal useful information in this case.

I'm assuming here as with other similar posts that the basics have been 
covered prior to getting to this point.  That includes cap, rotor, plugs all 
good and air filter changed as air flow sensor checked to be operating 
freely and cleaned.  Don't assume your Jiffy-Tune boys did any of this.

Don't even think of messing with DPR until you have ruled other things out. 
If you think that may be it there is a way to remove and clean it.

Ben

[Date: Wed, 05 Oct 2005 09:10:12 -0400
From: Kent McLean <kentmclean at mindspring.com>
Subject: Re: 1988 Audi 90 - Air-Fuel Mixture Problem
To: schief53562 at peoplepc.com
Cc: quattro at audifans.com
Message-ID: <4343D0B4.6000804 at mindspring.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

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]