Volvo: 94 Volvo 850 Fouled Sparkplug problem, volvo 850, newer cars

Question
Ray, does this make any sense?

1994 Volvo 850

Problem: Reoccuriong fouled sparkplugs.  Engine won't start.  Dealer can not find problem, just sees the results.

Sequence:

Car operation normal.

Tank filled with petrol.

Gas fumes in garage.

With a couple days or so, car started, backed up about 15 yards, left for an hour or so.  Car started with no problem and pulled back into garage.  Total movement 30 yards, backing and forward.  Would not start the next try!!

I know for sure this was the January 09 and April 09 scenario.  I also clearly remember it once before and suspect it has been the problem every time.

Question: Is this creating a fleeting circumstance, vacuum pull down of oil, anything that would cause the sparkplug fouling problem but not show up on their computers despite a full range of tests?  If not why do the same conditions prevail in at least 3 occasions that I am sure of as correct.  I suspect it is true in every instance.

I would bet that if the car were driven around before returning to the garage, the problem would not occur.  Ray, if you have any suggestion it will be more than we have now.  For example, how about once it is fixed again it must always be driven for a few miles before returning to garage.  Do you think this would help?

Thanks, Harris Johnson


Answer
Harris,
If the car is started and stopped without time for the engine to warm up that can cause the plugs to foul and contaninate the oil with fuel. Those conditions are not good for the car.
The diagnostics on a 94 are not as good as the newer cars so the information is not as great or reliable.
If your plugs are oil fouling then look for a valve guide or seal problem.