You can't possibly have too much vacuum, but you could have vacuum applied when it shouldn't be.
For instance, I suspect you have a faulty PCV valve. This is an emissions device that pulls excessive "blow-by" gasses from you crankcase and introduces them into the intake manifold to be burned with normal air/fuel mixtures.
When this valve is bad, it will sometimes pull oil into the intake manifold as well ass the normal gasses. As long as the oil is only getting down stream of the MAF sensor, you won't have anything to worry about. But if this valve is bad, I'd replace it anyway.
As for your O2 sensor, just because the computer set a code for "O2 sensor, bank 1", doesn't mean the sensor was bad. All the computer is trying to tell you is there's something wrong with that particular system. This could be the sensor, the circuit (wiring/connector), or anything that could effect this circuit, such as a clogged fuel injector causing a lean condition, an exhaust restriction causing faulty readings, etc.
When you get a code like this, it isn't wise to just replace components. You need to do a thorough diagnosis to find out the underlying cause of the problem. Because as you see, it's possible to replace a component just to have the same problem.
So what you need to do is scan your computer with a capable scanner that can give you "live monitors". This will tell you what that sensor is reading. If it's reading a rich condition, then you should look at the possibility of a misfire for that cylinder. (No spark) If you're getting a lean condition, then I'd look at a clogged/failing fuel injector.
But there's other possible causes to you code. You'll just have to hunt it down. Good luck.
Tuesday, April 27th, 2010 AT 6:08 PM