I have an idle problem ('86 5000CD QT) that was intermittent but is becoming
more regular. Some idle adjustments a couple of months
ago made the problem "go away" but then the problem started appearing again
The car starts no problem when hot or cold (also has had fuel accumulator
removed) but won't start for a couple of minutes if the
hot engine dies when it fails to idle. The engine tries to adjust the idling and
most of the time succeeds but for the last two
days, when the engine is hot and operating, when I let go of the gas it dies and
then I can't start it for a couple of minutes. If
the engine dies when I'm moving I put it in gear and it starts again no problem.
Then today I drove the car for a couple of hours
and the problem only occurred once. Other than that, the engine idles very
smoothly and I never sense a loss of power. I've gone
over the various threads and haven't found a solution yet. I've cleaned the idle
stabilization valve (engine dies when I disconnect
cable) and the injectors seem fine (I've run injector cleaner already). All the
various ignition parts have been replaced. All
filters have been replaced. We have what we call AirCare here in British
Columbia and it passed like a new car (so said the
mechanic) with 0 CO and everything else WELL below average. So it's probably not
the oxygen sensor.
Any ideas what it could be? Electrical connection? (but if so, the car does
start fine when put in gear when moving....)
Other than, it's quite an amazing car for something 20 years old.
Thanks for any help,
It sounds like you are familiar with the ISV system and have established that it
is functioning correctly. Therefore my guess is that you have a vacuum leak that
is somewhat intermittent (those are the most fun).
Have you tried the T44Q back yard vacuum test?
- Engine idling: pull oil dip stick - engine should falter and begin to run
- Replace dip stick.
- Remove oil filler cap - engine should die.
If not you have a vacuum leak.
First place to look is the Michelenman hose (front of intake manifold). You need
to remove it to check carefully for cracks on the bottom side. After that check
the crankcase breather. After that check all other possible lines. Don't forget
the decel valve in the passenger fender hidden behind the fuel distributor. If
the decel is the problem it can be disconnected with little effect on
driveability and plug the line.
I will check those, I noticed one of the lines was plugged. Also, when I squeeze
what you call the Michelin Man hose the engine
falters or dies if squeezed stronger, that's normal, right? (it's being choked
Thank you very much Tony for your help, it gives me something to go at. I took
it to a known Audi fuel injection expert and he
couldn't figure it out, I suppose if I threw money at it then he could probably
solve, but the car is basically worthless (market
wise), so I guess I'll try to figure it out myself, it's more fun that way. =)
The fact that the engine dies when you unplug the ISV indicates that it is
operating. this includes the ISV itself, the wiring, the ISV controller, temp
sensor and closed idle switch on the throttle body (which tells the controller
to operate the ISV).
I think that what you indicated in your other email is a strong clue to the
problem. You said that the engine falters and dies when you squeeze the MM hose.
I don't think that is due to the compression but rather that the offending split
in the the bottom of the hose is opening and creating a vacuum leak. Replacing
the MM may be the fix.
Check the on line sites for a replacement:
(great reference site and also a good parts supplier)
I am not sure if these ship to Canada but worth a try.
Tony, the MM hose fixed the problem! I owe you big time, stop by for a beer when
in Vancouver! =)
There was a 2cm rip in the bottom part of the hose, now the car drives great,
didn't know it had that much power, at round 5000rpm,
for a heavy car it takes off like a pocket rocket! =)
Good to hear you got it corrected and have now discovered the potential of these
great engines. I'll be sure to collect the beer when in the neighborhood. It
couldn't be more than 1,200 miles from Minneapolis :-)
Enjoy the ride.
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