I have a 1987 Audi 4000CS Quattro with 145000 miles on it. The car
currently runs very rough, with the following symptoms:

1) Idle warbles between 800 and 2000 rpm
2) car shudders and lurches, as if it isn't getting enough fuel, when
coasting downhill or accelerating uphill. It is roughest when I step
on the accelerator or suddenly release the accelerator with the car
still in gear.

I had the O2 sensor and the idle valve replaced, as well as the cold
start valve. The only known issue with the car is a hole in the
muffler - my guess is that somehow the hole in the muffler is
distorting whatever sensors are in the exhaust system?

I am considering replacing the muffler, but wanted to have a better
sense that it is causing this problem.

Thanks for any advice, Audi fans!

 

Idle and rough running sounds like some combination of:
vacuum leaks:

Vacuum leaks: check by removing the oil filler cap wen running. It
should cause engine to die. Remove dipstick when idling. It should cause
engine to run bad and nearly die. If either of these don't cause bad
running, check all vacuum lines and repair as necessary.

dirty fuel filter: replace if dirty or old

dirty Idle Stabilization Valve: remove and clean with brake cleaner
spray and dry well. Check the closed throttle switch in the throttle
body to be sure it is telling the ECU to ISV.

May want to try injector cleaner too.

Tony
'91 100Q 5spd

Chris Donahue wrote:
> I have a 1987 Audi 4000CS Quattro with 145000 miles on it. The car
> currently runs very rough, with the following symptoms:
>
> 1) Idle warbles between 800 and 2000 rpm
> 2) car shudders and lurches, as if it isn't getting enough fuel, when
> coasting downhill or accelerating uphill. It is roughest when I step
> on the accelerator or suddenly release the accelerator with the car
> still in gear.
>
> I had the O2 sensor and the idle valve replaced, as well as the cold
> start valve. The only known issue with the car is a hole in the
> muffler - my guess is that somehow the hole in the muffler is
> distorting whatever sensors are in the exhaust system?
>
> I am considering replacing the muffler, but wanted to have a better
> sense that it is causing this problem.
>
> Thanks for any advice, Audi fans!

 

Like TonyJ says, check the 'closed throttle switch' -- it's below the
throttle butterfly casting (opposite the switch that detects
full-trottle which is on top). My 2.2L 5-cyl did the same lurching
and idle warbling, until someone else suggested I check this switch.
I just soaked it with WD40 and voila!

Jaz

>dirty Idle Stabilization Valve: remove and clean with brake cleaner
>spray and dry well. Check the closed throttle switch in the throttle
>body to be sure it is telling the ECU to ISV.
>
>May want to try injector cleaner too.
>
>Tony
>'91 100Q 5spd
>
>Chris Donahue wrote:
>> I have a 1987 Audi 4000CS Quattro with 145000 miles on it. The car
>> currently runs very rough, with the following symptoms:
>>
>> 1) Idle warbles between 800 and 2000 rpm
>> 2) car shudders and lurches, as if it isn't getting enough fuel, when
>> coasting downhill or accelerating uphill. It is roughest when I step


{ Please excuse the 'burp' when replying }
¨"°ºOº°"¨¨"°ºOº°"¨¨"°ºOº°"¨¨"°ºOº°"¨"°ºOº°"¨

 

Chris/Tony,
Do normally aspirated (aka non-turbocharged) engines stall when the oil cap
is removed? My '80 5kS (ok, it's not the same engine, etc.) runs fine when
you remove the cap - see the camshaft merrily spinning in there - flinging
oil out and everything. (then again, my '80 doesn't have a O2 sensor,
so....) You're right on with the vacuum leaks - check the big rubber meter
to throttlebody corrugated boot - they often have cracks on the underside.
Don't use brake cleaner on the ISV, though....yikes!!! Brake cleaner is way
too agressive and will destroy the rubber seal in there. Use throttlebody
cleaner - even carb cleaner will damage the rubber. Spray the stuff in and
use a 9 volt battery - yes, 9v, not 12 - to operate the valve open and
closed a few times.
The hole in the muffler will also decrease the backpressure in the system,
try patching it with whatever muffler bandage you can get/make and take the
car for a drive to see what has changed/improved.
Cheers!
Steve Sears
1987 Audi 5kTQ
1980 Audi 5k
1962 and '64 Auto Union DKW Junior deLuxes
(SPAM Blocker NOTE: Remove SHOES to reply)

"TonyJ" <tonyjNOSPAM@NOSPAMvisi.com> wrote in message
news:3f68e12d$0$172$a1866201@newsreader.visi.com.. .
> Idle and rough running sounds like some combination of:
> vacuum leaks:
>
> Vacuum leaks: check by removing the oil filler cap wen running. It
> should cause engine to die. Remove dipstick when idling. It should cause
> engine to run bad and nearly die. If either of these don't cause bad
> running, check all vacuum lines and repair as necessary.
>
> dirty fuel filter: replace if dirty or old
>
> dirty Idle Stabilization Valve: remove and clean with brake cleaner
> spray and dry well. Check the closed throttle switch in the throttle
> body to be sure it is telling the ECU to ISV.
>
> May want to try injector cleaner too.
>
> Tony
> '91 100Q 5spd
>
> Chris Donahue wrote:
> > I have a 1987 Audi 4000CS Quattro with 145000 miles on it. The car
> > currently runs very rough, with the following symptoms:
> >
> > 1) Idle warbles between 800 and 2000 rpm
> > 2) car shudders and lurches, as if it isn't getting enough fuel, when
> > coasting downhill or accelerating uphill. It is roughest when I step
> > on the accelerator or suddenly release the accelerator with the car
> > still in gear.
> >
> > I had the O2 sensor and the idle valve replaced, as well as the cold
> > start valve. The only known issue with the car is a hole in the
> > muffler - my guess is that somehow the hole in the muffler is
> > distorting whatever sensors are in the exhaust system?
> >
> > I am considering replacing the muffler, but wanted to have a better
> > sense that it is causing this problem.
> >
> > Thanks for any advice, Audi fans!
>

 

Jaz <harbellburp@beer.com> wrote in message news:<p5shmvck0so63vi92jsmuc41chnpkrsrvc@4ax.com>. ..
> Like TonyJ says, check the 'closed throttle switch' -- it's below the
> throttle butterfly casting (opposite the switch that detects
> full-trottle which is on top). My 2.2L 5-cyl did the same lurching
> and idle warbling, until someone else suggested I check this switch.
> I just soaked it with WD40 and voila!

While you're at it, pay particular attention to the big rubber 'vacuum
junction' the ISV plugs into. It has about 5 different sized
appendages going off in weird directions from it. It tends to get
hard (from engine heat, IMO) on the bottom and cracks there. It's not
very expensive or difficult to replace and is quite possibly your
problem. As a very temporary measure, you can slap some RTV goop on
the crack and wrap it with about 20 feet of duct tape (The Handyman's
Friend) and let it cure overnight before driving it. Don't expect
that to last even a week. Just long enough for your special-ordered
new one to come in.

OTOH, all of us have avoided mentioning the $$$ po$$ibility: the fuel
differential pressure regulator. It's the little grey-green
electronic thing on the front of the fuel distributor with two screws
and a connector going to it. It's labeled "Bosch", which explains its
$260+ price tag. At least you can install it in under 5 minutes ...
--
C.R. Krieger
(Been there; done that - on the road)

 

Steve, thanks for correcting the ISV cleaner recommendation I made.

The oil filler cap does kill mine when I remove it. My '91 is of course
the NA NF engine and does have an O2 sensor. I wouldn't think that the
O2 sensor would be involved in that check because it should only be
affecting the timing and not the vacuum system.

Tony
'91 100Q 5spd

Steve Sears wrote:
> Chris/Tony,
> Do normally aspirated (aka non-turbocharged) engines stall when the oil cap
> is removed? My '80 5kS (ok, it's not the same engine, etc.) runs fine when
> you remove the cap - see the camshaft merrily spinning in there - flinging
> oil out and everything. (then again, my '80 doesn't have a O2 sensor,
> so....) You're right on with the vacuum leaks - check the big rubber meter
> to throttlebody corrugated boot - they often have cracks on the underside.
> Don't use brake cleaner on the ISV, though....yikes!!! Brake cleaner is way
> too agressive and will destroy the rubber seal in there. Use throttlebody
> cleaner - even carb cleaner will damage the rubber. Spray the stuff in and
> use a 9 volt battery - yes, 9v, not 12 - to operate the valve open and
> closed a few times.
> The hole in the muffler will also decrease the backpressure in the system,
> try patching it with whatever muffler bandage you can get/make and take the
> car for a drive to see what has changed/improved.
> Cheers!
> Steve Sears
> 1987 Audi 5kTQ
> 1980 Audi 5k
> 1962 and '64 Auto Union DKW Junior deLuxes
> (SPAM Blocker NOTE: Remove SHOES to reply)
>
> "TonyJ" <tonyjNOSPAM@NOSPAMvisi.com> wrote in message
> news:3f68e12d$0$172$a1866201@newsreader.visi.com.. .
>
>>Idle and rough running sounds like some combination of:
>>vacuum leaks:
>>
>>Vacuum leaks: check by removing the oil filler cap wen running. It
>>should cause engine to die. Remove dipstick when idling. It should cause
>>engine to run bad and nearly die. If either of these don't cause bad
>>running, check all vacuum lines and repair as necessary.
>>
>>dirty fuel filter: replace if dirty or old
>>
>>dirty Idle Stabilization Valve: remove and clean with brake cleaner
>>spray and dry well. Check the closed throttle switch in the throttle
>>body to be sure it is telling the ECU to ISV.
>>
>>May want to try injector cleaner too.
>>
>>Tony
>>'91 100Q 5spd
>>
>>Chris Donahue wrote:
>>
>>>I have a 1987 Audi 4000CS Quattro with 145000 miles on it. The car
>>>currently runs very rough, with the following symptoms:
>>>
>>>1) Idle warbles between 800 and 2000 rpm
>>>2) car shudders and lurches, as if it isn't getting enough fuel, when
>>>coasting downhill or accelerating uphill. It is roughest when I step
>>>on the accelerator or suddenly release the accelerator with the car
>>>still in gear.
>>>
>>>I had the O2 sensor and the idle valve replaced, as well as the cold
>>>start valve. The only known issue with the car is a hole in the
>>>muffler - my guess is that somehow the hole in the muffler is
>>>distorting whatever sensors are in the exhaust system?
>>>
>>>I am considering replacing the muffler, but wanted to have a better
>>>sense that it is causing this problem.
>>>
>>>Thanks for any advice, Audi fans!
>>
>
>

 

Seems to me that I remember someone checking this by unplugging it. When
unplugged the engine ran, not well, but corrected the symptoms. This is
just a SWAG and others might have better information.

Tony
'91 100Q 5spd

C.R. Krieger wrote:

> Jaz <harbellburp@beer.com> wrote in message news:<p5shmvck0so63vi92jsmuc41chnpkrsrvc@4ax.com>. ..
>
>>Like TonyJ says, check the 'closed throttle switch' -- it's below the
>>throttle butterfly casting (opposite the switch that detects
>>full-trottle which is on top). My 2.2L 5-cyl did the same lurching
>>and idle warbling, until someone else suggested I check this switch.
>>I just soaked it with WD40 and voila!
>
>
> While you're at it, pay particular attention to the big rubber 'vacuum
> junction' the ISV plugs into. It has about 5 different sized
> appendages going off in weird directions from it. It tends to get
> hard (from engine heat, IMO) on the bottom and cracks there. It's not
> very expensive or difficult to replace and is quite possibly your
> problem. As a very temporary measure, you can slap some RTV goop on
> the crack and wrap it with about 20 feet of duct tape (The Handyman's
> Friend) and let it cure overnight before driving it. Don't expect
> that to last even a week. Just long enough for your special-ordered
> new one to come in.
>
> OTOH, all of us have avoided mentioning the $$$ po$$ibility: the fuel
> differential pressure regulator. It's the little grey-green
> electronic thing on the front of the fuel distributor with two screws
> and a connector going to it. It's labeled "Bosch", which explains its
> $260+ price tag. At least you can install it in under 5 minutes ...
> --
> C.R. Krieger
> (Been there; done that - on the road)

 

Thanks all for your suggestions. I'll try some of them out this
weekend, and if I get stuck, will bring a printout down to my mechanic
(Tony Dvorak at Euro Quattro in Mountain View, CA, in case any of you
are from the area) next week.

My last symptom which I forgot to mention is that the car runs much
better at highway speeds than at slower speeds. If it is a vaccuum
problem, is it possible that high speeds makes the vaccuum issue less
noticable?

Thanks again,

Chris

TonyJ <tonyjNOSPAM@NOSPAMvisi.com> wrote in message news:<3f69f571$0$188$a1866201@newsreader.visi.com> ...
> Steve, thanks for correcting the ISV cleaner recommendation I made.
>
> The oil filler cap does kill mine when I remove it. My '91 is of course
> the NA NF engine and does have an O2 sensor. I wouldn't think that the
> O2 sensor would be involved in that check because it should only be
> affecting the timing and not the vacuum system.
>
> Tony
> '91 100Q 5spd
>
> Steve Sears wrote:
> > Chris/Tony,
> > Do normally aspirated (aka non-turbocharged) engines stall when the oil cap
> > is removed? My '80 5kS (ok, it's not the same engine, etc.) runs fine when
> > you remove the cap - see the camshaft merrily spinning in there - flinging
> > oil out and everything. (then again, my '80 doesn't have a O2 sensor,
> > so....) You're right on with the vacuum leaks - check the big rubber meter
> > to throttlebody corrugated boot - they often have cracks on the underside.
> > Don't use brake cleaner on the ISV, though....yikes!!! Brake cleaner is way
> > too agressive and will destroy the rubber seal in there. Use throttlebody
> > cleaner - even carb cleaner will damage the rubber. Spray the stuff in and
> > use a 9 volt battery - yes, 9v, not 12 - to operate the valve open and
> > closed a few times.
> > The hole in the muffler will also decrease the backpressure in the system,
> > try patching it with whatever muffler bandage you can get/make and take the
> > car for a drive to see what has changed/improved.
> > Cheers!
> > Steve Sears
> > 1987 Audi 5kTQ
> > 1980 Audi 5k
> > 1962 and '64 Auto Union DKW Junior deLuxes
> > (SPAM Blocker NOTE: Remove SHOES to reply)
> >
> > "TonyJ" <tonyjNOSPAM@NOSPAMvisi.com> wrote in message
> > news:3f68e12d$0$172$a1866201@newsreader.visi.com.. .
> >
> >>Idle and rough running sounds like some combination of:
> >>vacuum leaks:
> >>
> >>Vacuum leaks: check by removing the oil filler cap wen running. It
> >>should cause engine to die. Remove dipstick when idling. It should cause
> >>engine to run bad and nearly die. If either of these don't cause bad
> >>running, check all vacuum lines and repair as necessary.
> >>
> >>dirty fuel filter: replace if dirty or old
> >>
> >>dirty Idle Stabilization Valve: remove and clean with brake cleaner
> >>spray and dry well. Check the closed throttle switch in the throttle
> >>body to be sure it is telling the ECU to ISV.
> >>
> >>May want to try injector cleaner too.
> >>
> >>Tony
> >>'91 100Q 5spd
> >>
> >>Chris Donahue wrote:
> >>
> >>>I have a 1987 Audi 4000CS Quattro with 145000 miles on it. The car
> >>>currently runs very rough, with the following symptoms:
> >>>
> >>>1) Idle warbles between 800 and 2000 rpm
> >>>2) car shudders and lurches, as if it isn't getting enough fuel, when
> >>>coasting downhill or accelerating uphill. It is roughest when I step
> >>>on the accelerator or suddenly release the accelerator with the car
> >>>still in gear.
> >>>
> >>>I had the O2 sensor and the idle valve replaced, as well as the cold
> >>>start valve. The only known issue with the car is a hole in the
> >>>muffler - my guess is that somehow the hole in the muffler is
> >>>distorting whatever sensors are in the exhaust system?
> >>>
> >>>I am considering replacing the muffler, but wanted to have a better
> >>>sense that it is causing this problem.
> >>>
> >>>Thanks for any advice, Audi fans!
> >>
> >
> >

 

That would be my guess.

Tony
'91 100Q 5spd

Chris Donahue wrote:
> Thanks all for your suggestions. I'll try some of them out this
> weekend, and if I get stuck, will bring a printout down to my mechanic
> (Tony Dvorak at Euro Quattro in Mountain View, CA, in case any of you
> are from the area) next week.
>
> My last symptom which I forgot to mention is that the car runs much
> better at highway speeds than at slower speeds. If it is a vaccuum
> problem, is it possible that high speeds makes the vaccuum issue less
> noticable?
>
> Thanks again,
>
> Chris
>
> TonyJ <tonyjNOSPAM@NOSPAMvisi.com> wrote in message news:<3f69f571$0$188$a1866201@newsreader.visi.com> ...
>
>>Steve, thanks for correcting the ISV cleaner recommendation I made.
>>
>>The oil filler cap does kill mine when I remove it. My '91 is of course
>>the NA NF engine and does have an O2 sensor. I wouldn't think that the
>>O2 sensor would be involved in that check because it should only be
>>affecting the timing and not the vacuum system.
>>
>>Tony
>>'91 100Q 5spd
>>
>>Steve Sears wrote:
>>
>>>Chris/Tony,
>>>Do normally aspirated (aka non-turbocharged) engines stall when the oil cap
>>>is removed? My '80 5kS (ok, it's not the same engine, etc.) runs fine when
>>>you remove the cap - see the camshaft merrily spinning in there - flinging
>>>oil out and everything. (then again, my '80 doesn't have a O2 sensor,
>>>so....) You're right on with the vacuum leaks - check the big rubber meter
>>>to throttlebody corrugated boot - they often have cracks on the underside.
>>>Don't use brake cleaner on the ISV, though....yikes!!! Brake cleaner is way
>>>too agressive and will destroy the rubber seal in there. Use throttlebody
>>>cleaner - even carb cleaner will damage the rubber. Spray the stuff in and
>>>use a 9 volt battery - yes, 9v, not 12 - to operate the valve open and
>>>closed a few times.
>>>The hole in the muffler will also decrease the backpressure in the system,
>>>try patching it with whatever muffler bandage you can get/make and take the
>>>car for a drive to see what has changed/improved.
>>>Cheers!
>>>Steve Sears
>>>1987 Audi 5kTQ
>>>1980 Audi 5k
>>>1962 and '64 Auto Union DKW Junior deLuxes
>>>(SPAM Blocker NOTE: Remove SHOES to reply)
>>>
>>>"TonyJ" <tonyjNOSPAM@NOSPAMvisi.com> wrote in message
>>>news:3f68e12d$0$172$a1866201@newsreader.visi.co m...
>>>
>>>
>>>>Idle and rough running sounds like some combination of:
>>>>vacuum leaks:
>>>>
>>>>Vacuum leaks: check by removing the oil filler cap wen running. It
>>>>should cause engine to die. Remove dipstick when idling. It should cause
>>>>engine to run bad and nearly die. If either of these don't cause bad
>>>>running, check all vacuum lines and repair as necessary.
>>>>
>>>>dirty fuel filter: replace if dirty or old
>>>>
>>>>dirty Idle Stabilization Valve: remove and clean with brake cleaner
>>>>spray and dry well. Check the closed throttle switch in the throttle
>>>>body to be sure it is telling the ECU to ISV.
>>>>
>>>>May want to try injector cleaner too.
>>>>
>>>>Tony
>>>>'91 100Q 5spd
>>>>
>>>>Chris Donahue wrote:
>>>>
>>>>
>>>>>I have a 1987 Audi 4000CS Quattro with 145000 miles on it. The car
>>>>>currently runs very rough, with the following symptoms:
>>>>>
>>>>>1) Idle warbles between 800 and 2000 rpm
>>>>>2) car shudders and lurches, as if it isn't getting enough fuel, when
>>>>>coasting downhill or accelerating uphill. It is roughest when I step
>>>>>on the accelerator or suddenly release the accelerator with the car
>>>>>still in gear.
>>>>>
>>>>>I had the O2 sensor and the idle valve replaced, as well as the cold
>>>>>start valve. The only known issue with the car is a hole in the
>>>>>muffler - my guess is that somehow the hole in the muffler is
>>>>>distorting whatever sensors are in the exhaust system?
>>>>>
>>>>>I am considering replacing the muffler, but wanted to have a better
>>>>>sense that it is causing this problem.
>>>>>
>>>>>Thanks for any advice, Audi fans!
>>>>
>>>

 

I got this problem fixed at Advanced Audi VW in San Francisco
(415-901-7270) - the problem turned out to be a bad vacuum advance,
and a broken ground for the fuel injector (broken at the manifold).
With these replaced, the car ran perfectly. Thanks all for the
suggestions - hope this dialog proves useful to someone in the future.