Volvo Repair: 1989 Volvo 760 injection problem, volvo 760, oil consumption

Question
Hello,

I recently bought 1990 Volvo 760 with 2nd generation PRV V-6 engine + AW automatic transmission. The car has 140.000 km, one owner, I bought it from the son of that owner who was very happy to get rid of the car and it was obvious that in the recent times it was not very well kept (bad tyres, no knowledge of when the engine oil was replaced, let alone other maintenance etc. It worked well in all aspects at the moment of purchase though.

I replaced the engine oil, sparkplugs, air filter, didn't have time to adjust the valves (not noisy) and we went on a long trip of 2000 km to Switzerland and back to Holland. The car drove superb, no problems, no oil consumption, fuel consumption +/- 10-11 lit, very fast driven.

On return from the trip petrol tank was almost empty, I wanted to do some more work on the car and did not fill it too much with petrol, then it went low again (the lamp for low petrol level is on), and then the problem started: first it was not that much visible, but revs would go up and down when idling. I didn't like that, and did not use the car extensively - maybe it worked all in all half hour after i noticed the problem, I left it in my garage for one month waiting for more time to deal with the car. Today I took it out of the garage, the same slight rev up and down was there, but it looked as if it did not hamper normal driving - I drove it like 20 min - then it started to be more and more - revs would go up to 2.000rpm and down almost to zero, it started to create problems in driving - weak power, occasionally better performance, occasionally very bad, with occassionally black smoke visible from the exhaust (not extremely bad), so I drove it back to my place in 2nd gear and now I am waiting to see what will happen when it cools down.

The temperature of the engine is normal, it will start without problems, lambda son warning light is not lit, but it will rev up and down from few hundred rpms to 2000 or more, and it will not accept the throttle i.e. accelerate the engine normally.

What should be the way to address the problem - going to local Volvo dealer is out of the question; they will probably destroy the car, it is not a good place to have such cars.

Thanks and best regards,

Dusan ilic
Netherlands

Answer
Dusan, try this simple trick.  If you know what the idle speed motor is then start the car and hit that idle motor with a hammer and see if anything changes.  That is the usual culprit on those engines.  It may be an air mass meter issue as well.  Roger