UPDATE: 1990 Coupe 2.3E 10v - jerkiness/poor driveability

Sat Feb 15 08:33:40 EST 2003

Dear Listers,

Thanks very much for your replies. I tried a few things over Christmas (including reading books on Bosch fuel injection) but I soon ran out of patience. So I took the car to a local Audi independent specialist who were very helpful. They tested about everything they could think of, and then said that applying the Motorvac machine to the fuel system may help. They said this would cost £70 GBP but would give all the injectors, valves and fuel supply system a thorough cleaning and might rule out injector problems. As I'd read good things about Motorvac elsewhere, I gave it a try. Didn't actually help as it happened, although apparently a lot of  dirt came out! Oh well. HOWEVER, while the mechanics were connecting the Motorvac to my car, they removed the electrical connection to the airflow potentiometer. After they'd finished, they forgot to plug it back in. Hey presto - stumbling and lurching GONE, smooth running returned! Plug the potentiometer lead back in, and the old problems were there again.

So where does that leave me? I now have a workaround, but not a fix. It seems that with the potentiometer disconnected, I lose the ECU idle control (this is a CIS III system), so the car is keen to stall when cold. I decided to take the car away anyway, but they offered to take it back if I wanted to investigate further.I am now looking for suggestions as to what to do next: -

1. I gather that it may not necessarily be a faulty airflow potentiometer, but could be something else related - is that so? I am guessing that it is giving a spiky output, but I supposed it might be the connection to it that is dirty - I'll need to check that.

2. If it *is* a faulty potentiometer, is the only solution to replace it (which I gather is about £200 GBP or would it be possible to split the unit apart and clean it?

I'd be very grateful of any suggestions you may have.

Thanks very much

Marcus

----- Original Message -----
From: Dave Kase <davekase at pdqlocks.com>
Date: Wed, 18 Dec 2002 11:22:35 -0500
To: "''Marcus Oxer''" <mdoxer at mail.com>
Subject: RE: 1990 Coupe 2.3E 10v - jerkiness/poor driveability

Marcus,

I am by no means an expert but I have experienced similar problems with mt
last CQ.

If you unplug the ISV and it not making a difference might indicate that
the ISV is not doing it's job.  I ran my last CQ with the ISV unplugged all
the time.  It does not make an a big difference.  It can only be noticed
when shifting or when starting the car cold.

When shifting, the engine speed drops off hard (without the control of the
ISV) and the engine tends to buck as the clutch is let out and the engine
has already stalled or almost stalled.  IF shifts are done smoothly it is
often not noticeable.

It couldnpt hurt to try the clean on the ISV, it's cheap!

Again, I am just guessing. there are some folks on the list that may be
able to help more.

Good luck,
Dave

-----Original Message-----
From:	Marcus Oxer [SMTP:mdoxer at mail.com]
Sent:	Wednesday, December 18, 2002 10:59 AM
To:	davekase at pdqlocks.com; 'Marcus Oxer'; quattro at audifans.com
Subject:	RE: 1990 Coupe 2.3E 10v - jerkiness/poor driveability

Hi Dave,

I confess that I have suspected my ISV in the past when I have had a
varying idle problem. However, even when I unplugged its electrical
connection, it didn't seem to make any appreciable difference to the
running of the engine. I was expecting lots of accidental stalling without
the ISV in play but this didn't seem to happen. Might that mean that my
idle speed is set too high - above the level at which the ISV takes over?

Apologies if I am not understanding it properly...!

Marcus

----- Original Message -----
From: Dave Kase <davekase at pdqlocks.com>
Date: Wed, 18 Dec 2002 10:08:59 -0500
To: "''Marcus Oxer''" <mdoxer at mail.com>, "quattro at audifans.com"
<quattro at audifans.com>
Subject: RE: 1990 Coupe 2.3E 10v - jerkiness/poor driveability

I'm thinking ISV.

Check www.20v.org for the cleaning instructions.

Dave K.
'90 CQ 20v

-----Original Message-----
From:	Marcus Oxer [SMTP:mdoxer at mail.com]
Sent:	Wednesday, December 18, 2002 9:31 AM
To:	quattro at audifans.com
Subject:	1990 Coupe 2.3E 10v - jerkiness/poor driveability

Dear Listers,

I wonder if you can offer any ideas on the following? It seems to have
confounded both my local Audi dealer and a Bosch Injection specialist...

The engine has recently started bucking, or jerking under very light
throttle openings - both as I go on the gas, and as I come off it. If I
hold the throttle in the same position, the car will continue bucking in a
most unpleasant way. Putting my foot down seems to smooth everything out -
it's really only a problem if the throttle is held steady with the car
under light load.

With the car at standstill and out of gear, I have noticed that if I slowly
build up the revs it is quite smooth up to 1800 rpm, at which point it
starts to stumble and miss beats in quite a random way.

I have recently replaced everything on the HT side - spark plug leads,
distributor cap, rotor arm, in order to cure a different under-load
misfire. The spark plugs have just been replaced as part of an Audi dealer
service.

My Bosch specialist said that the (non-original) replacement spark plug
leads might be causing a problem as he has seen cases where they are
insufficiently suppressed and interfere with the ECU. I have reverted to
the old leads but the problem still persists.

Reading through the archives, I am wondering whether components such as
ISV, throttle position switch, and oxygen sensor could be implicated.
However, I am not getting any error codes and also I presumed these are the
sort of things that would have been ruled out by the Bosch engineer. He
charged me ?55 GBP for a diagnostic check, but couldn't find an obvious
fault.

Any ideas would be gratefully received!!!

Marcus Oxer
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