Ken,

I want to start by saying that this isn't my cockamamy story. It is the result of seeing this firsthand and also is borne out by the bulletin from Volvo where they have tou drive the car @ high revs to get valves cleaned.

First, The valve springs on 4 vlave/cyl engines are weaker due to the valves being smaller and lighter and not requiring as much closing force from springs.

Second, hydraulic tappets by design exert some force towards oepning the valve due to the oil pressure that is inside pushing on the adjusting plunger. The surface area of the plunger is small so the force of spring closing valve is normally far greater than the opening force exerted by tappet adjusting plunger.

Third, the valves are not hanging wide open but rather are being held open only around 1 mm by the tappet. The tappet opening force is greater for a period of time when the valve is not being full force closed by spring due to the exh valve deposits and the tappet has the opportunity to "pump up" and thus keep the valve from closing fully.

The causes of this are numerous. It takes a certain driving style, a certain fuel detergent level, a certain oil detergent breakdown, etc.

AND THE MOST IMPORTANT THING IT TAKES is the short run, sit for a period, short run, and then sit, and then try to start.

Many many more people will never have this occur that will ever have it occur. The conditions may not all be met and then it won't happen. Better spark plugs with more resistance to fouling will decrease the likelihood of it happening as getting the rpms to a bit higher level during the initial firing of the cold cranking motor will ecercise the valves faster and the time the tappets have to "pump up" is decreased so they never get a chance to hold the valve off seat the miniscule amount it takes to get compression low enough to fail to run.

The "rings are washed down" theory fails as piston rings that get "washed down" (oil film on cyl wall gets dissolved by excess fuel from flooding and makes rings not seal) will only occur on an engine that has some notable ring wear and rings not sealing does not give you the almost zero, if not zero, compression readings you will find in an engine with valves that are held open (held open is a better term because "stuck open" is what I think has given you the problem to begin with).