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Oxygen censor

I have a 1994 MPV V6 3.0.I was having trouble with the car occasionally revving up to 3000 and not kicking into gear, and sometimes it wouldn’t start, just turn over. My uncle thought it was the oxygen censor. He cleaned it out. Test drove it for a week and gave it back. We filled it up with gas and forgot the gas cap. We drove it for a week with no gas cap and it drove fine. We replace the gas cap and the car won’t move. It just revs up. I take the gas cap back off, and it runs fine. What do you think?

O2 sensor read the amount of emissions coming out of the combustion chamber and send information to the ECM which then adjusted the about of fuel to be burned. That’s all. The gas cap part confuses me. That gas cap is used to seal the fuel tank and any fumes are collected in the charcoal canister and later burned as the engine is run. You have the earlier style computer system but, they can still be checked for any codes. It amazes me a check engine light hasn’t come on.

That is weird, isn’t it? The only thing that comes to mind is the gas cap vent is blocked, but that would act slightly different. Still a gas cap is cheap.

But, that would not involve 3000 rpm and no power to wheels. Nor revving up instead of moving.

Frankly, I suspect more than one problem in this car. Murphy does strange things, but it sure looks like separate problems.

Assuming it has an automatic transmission, have a knowledgeable person look at automatic transmission fluid and level. Low fluid could explain part of this problem, and horrid coincidence could explain more. One step at a time, check that fluid first. Low fluid will cause engine revving and car not moving. Eliminate one thing at a time.

We checked the transmission fluid and it’s ok. There are no leaks. Could it be that with the gas cap off, it’s allowing more oxygen to mix in with the gas? Oil is ok.The car just had a tune up. My uncle said when I bought it in August that the car sat for at least 6 months.
Well… I just drove it again and the same thing happened, even without the gas cap.

As irlandes suggests and as you seem to now maybe have figured out there is no way that having the gas cap off and the car not moving have anything to do with each. Nor do either of these things have to do with it not starting once in a while.

I’m thinking you just need a good, reputable, locally owned shop to look everything over. I also think it possible that this car might not be worth the trouble. You have some kind of transmission trouble and some kind of intermittent ignition or fuel problem. But you need a good experienced mechanic to look things over. (No offense to your uncle but cleaning an O2 sensor is a really strange thing to decide to do in response to this stuff).

This is a no-brainer. If it runs fine with the cap off, LEAVE THE CAP OFF! There are words that accurately describe what is going on, but if you use them on this board, they delete the post…