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Audi 5000: 1977-1983 (C2) Ongoing running problem 87 5kt

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Registered: 11/06/07
Ongoing running problem 87 5kt
Posted: Dec 9, 2009 7:32 PM
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This is a shot in the dark here because this forum is completely dead, but i'm hoping that someone might have a clue as to what is wrong. what I'm posting is a collaboration of things that I've posted on other sites while trying to figure this thing out....

All of my vac lines, except the charcoal canister ones are new(within 2 years), all of my temp sensors were replaced last year, along with my injectors, seals, etc...

The problem i'm having is sometimes the idle will be kinda irratic, and according to my NB AFR, the car falls pretty lean sometimes. and when I go to accelarate the engine will sputter/hesitate before finally smoothing out at approx 1600rpm. This has been an ongoing problem since I changed the vac lines on this car, the previous owners had everything really pretty botched up...

When we first bought the car like 3 years ago, she idled perfectly at 800, but was definitely lacking on power. Then as I learned more and started fixing things, she slowly started idling like crap. The idle screw and the metering head mixture screw both had definitely been messed with multiple times in the life of this car...

I went to check my CO adjustment(the metering head screw) the other day because I was having ISV problems, it had essentially stopped working so I just unplugged it and used my idle speed screw to keep the car idling till I got home. I cleaned my isv with throttle body cleaner, and it started working again so I went ahead and started to test things.

I know in theory the idle screw should be screwed all the way in, and let the ISV do it's job. This of course means that everything should be in good working order.

I turned the screw in as far as I could while it was running (and still have the throttle plate move) and the car started running like ****, and it wouldn't start in that position. so I put the screw back at where she idled happily around 750rpm and went to check my CO%/Duty Cycle. I don't remember the exact number right now, but it was a bit lean. I had a b*tch of a time getting it to be around 46-52% because of how irradic it was. Even now according to my NB AFR it is still all over the friggen place, going slightly more lean than I would like too.

and now I still have the same problems I was having before, that is when I go to hit the throttle it will stutter/miss a bit (according to my gauge, goes way lean) and then it will catch up and start going good. and if I rev and let of the gas real quickly it will bog down like she wants to stall until it catches back up, this might just be the effect of my BPV, but who knows.

now this is what I'm thinking... My metering plate could be sticking, there is a way to pop the control pin out and clean it up, or my CO/idle speed mixture needs some drastic messing around with.

As of today, I set the basic/zero adjustments on the metering head/plate and got the car to run pretty well, set my freq valve to be 50% avg duty cycle, and the car was idling pretty well, etc. Drove it around and had no problem, other then a little problem with cold starting. Until I went to drive back from the store, and the problem started up again as if I hadn't done anything. thats what the problem is here it's so intermittent it makes it hard to diagnose.

At this point I want to pull the pin out of the metering head, because I really do think it's sticking, and then check out if there is anything going on in the ISV control module. I also am thinking I should buy a new o2 sensor, even though I have no proof if mine is good or bad.....

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