I have a oil consumption problem that seems to be intermittent. I am using about 1 litre per 1000 km or about 1 qt in 600 miles. Sometimes, especially when the engine is well warmed up, there are large clouds of blue/white smoke from the tailpipe wnen idling at a stop light. People don't get very close behind. Usually, however, there is no smoke or smell at all. I can't figure out what might be sticky and intermittent. Maybe PCV valve?

On a related issue, what should the oil pressure meter be reading while at normal road speed and what at idle? I am showing about 3 bar at idle and 5 (the top of the meter) when engine speed is over about 1500 rpm. Any insights on what is the normal spread?

The car is a 90 CS Sport Quattro with Canadian setup and pollution controls.

Thanks in advance.

"Maybe a PCV valve?" Don't you wish?

Chances are that you need new valve guide seals to cure your oil consumption issue. When the engine operates at low manifold pressures like it does at idle, (high intake manifold vacuum) engine oil is getting sucked past the intake valve guide seals into the combustion chamber. It's also leaking past the exhaust valve guide seals and smoldering in the exhaust manifold. Does your vehicle have a few overheating events in it's past? Those tend to cook the valve guide seals much sooner than later.

At higher RPM's, the engine (or the catalytic converter) is burning the oil so chances are that you won't regularly see any blue smoke out the tailpipe then. (until the oil consumption rate gets down to about 200 miles per quart, then you will)

Check your spark plug condition for oil contamination and/or ash production per the attached chart.

Chumley

I also have a 1994 90 Quattro CS with the same problem. I found that the oil has being traveling through the breather tubes from the valve covers and going into the intake and had completely coated my intake manifold and throttle body with oil. The breather tubes were also full of sludge and milky oil from moisture. I am also wondering if the breather tubes, being somewhat clogged from sludge, are a factor to the problem. The plastic tubes are also old and brittle and broke as i removed them. I am still trying to determine if it is from blow-by issues or if it is being sucked out. I have tried removing the breather tubes and plugging the holes in the intake to see if the oil would blow out of the valve cover openings. So far it has stopped burning oil and there is no oil coming out of the valve covers. My new problem is figuring out if i were to purchase new breather tubes (which are around 100 dollars each) and install them, if the problem would return, or if it was just all because they were full of sludge. Another thing is that now that i have removed the breather tubes, my engine is now leaking a fair amount of oil when running. Any solutions you have found or that anybody knows of would be very much appreciated.