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Car Forum / Audi Cars / February 2006Intermittent Idle problem in '86 5000QT
Hello, 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 gradually. 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, cp 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 rough. - 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. > Hello, > [quoted text clipped - 17 lines] > Thanks for any help, > cp Hi Tony, > Have you tried the T44Q back yard vacuum test? Yes > - Engine idling: pull oil dip stick - engine should falter and begin to run rough. Yes > - Replace dip stick. > - Remove oil filler cap - engine should die. Yes > 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 of air?) 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. =) cp Also, > It sounds like you are familiar with the ISV system and have established that it is functioning correctly. Not too familliar. In this case, how would I know that the ISV is OK? (engine dies when unplugged?.....) cp 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: http://www.sjmautotechnik.com/ (great reference site and also a good parts supplier) http://www.ecstuning.com/ http://blauparts.com/ I am not sure if these ship to Canada but worth a try. > Also, > [quoted text clipped - 3 lines] > > cp > The fact that the engine dies when you unplug the ISV indicates that it is operating. Yeah, so I figured =) > 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. Will take a look, thank you (again) Tony! cp 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! =) THANKS! cp > 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). [quoted text clipped - 32 lines] >> Thanks for any help, >> cp 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. Tony > Tony, the MM hose fixed the problem! I owe you big time, stop by for a beer when in Vancouver! =) > [quoted text clipped - 40 lines] >>>Thanks for any help, >>>cp > Good to hear you got it corrected and have now discovered the potential of these great engines. Yes, didn't think a little engine like that would haul a heavy car this "lightly"! =) For five cyls, the engine doesn't even move a bit when idling >I'll be sure to collect the beer when in the neighborhood. It couldn't be more than 1,200 miles from Minneapolis :-) =) should be a nice ride on the I90, email me cplas at telus dot net if ever in town =) > Enjoy the ride. Fer sure! cp |
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