I have just purchased a 1985 4000S and it seems to have some problems I don't quite understand. I have a bit of experience working on cars, but Audi's are new to me. I just changed the oil and filter, and afterwards the oil light would come on and warning buzzer sound if I went over about 2000rpm. The problem usually goes away after a few minutes driving, but sometimes remains for over ten minutes. Also at a stop (car is automatic) the idle will ocassionally drop signifigantly and sometimes stall the car. It also sometimes refuses to rev up when the accellerator is depressed, instead stuttering and dropping revs/power. I like the car and would like to get it fixed up and running in top form. I would appreciate any advice. Thanks a lot.

 

check the oil dipstick seal if its worn it will leak compression which will make it idle erratic

 

If the car ran fine before the oil change then I would check the wiring and vacuum lines.

 

or the oil filler, on our 90 200tq if you remove the oil cap while its running the idle goes crazy and tries to die

 

Avant80 is spot on. I had the same issue on an '85 4000s about 15 years ago and it was the dipstick seal. Also check the gasket for the oil filter housing (not the one for the oil filter itself). Mine let go in a snowstorm and I thought it was just the buzzing thing again until I got home a few miles later to find oil dripping from the front of the car. Easy fix, but just about gave me a heart attack thinking the engine had let go.

 

Where is the oil dipstick seal? Is it where the dipstick tube meets the block or between the funnel and dipstick?

 

the dipstick is the part you pull out to check the oil level and the seal should be at the top which seals the tube when in place, on the yellow bit mate

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R u useing a good oil filter Mann, bosch no orange colord filters junk

 

the oil pressure sensors are a common problem on these type of cars ( one for high pressure one for low ) it is possiblle that you disturbed these when you changed the oil ... idle problem would most likely be a vacum leak ... check your hoses ... oil cap ... dipstick ... air filter housing and so on
Basicly the same advice