Int RPM problem, 92 Sunfire

Hi, I'm new to the newsgroup, but can't seem to find my problem here... I hope that you can help.
I have two problems, I'm not sure if they are related or not. The first
is minor. My oil pressure gauge works perfectly at idle, or if the rpm's are less than about 1200, but as soon as you step on the gas, the gauge goes crazy; up, down, and sometimes just pinned to the max side of the meter.
The other problem is the major one, but is intermittant. Once every couple of weeks, the car seems to lose its minimum idle speed. Normally it never idles much below 1000, but in this case it seems to cycle between 500 and 1000 about once every five seconds. The cycling is very rhythmic. Sometimes it stalls at the low end of the cycle. No error codes. I believe it has happened once or twice with a warm engine, but mostly with a cold engine.
I can solve the problem by turning off the engine, waiting five minutes, and restarting. (kind of like a microsoft solution).
I'm wondering if it is electrical -- some sensor, or the wire leading from it, but what sensor would cause this situation?
one possible related thing... I had to replace a cat a few months ago when I had my car inspected. Could a faulty O2 sensor have given these symptoms and caused the cat failure? I don't want to lose another cat.
92 Sunbird, 3.1L V6, Auto. 230,000km
Thanks for any suggestions
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the idle sensor is bad and for the oil pressure check and see if you have the right amount of oil and it could be a bad ground bad gauge
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jimmyh wrote:

Thank you. I'll try swapping it out and see what happens.
wazzoo
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Don't assume. A vacuum leak will also cause the symptoms he is describing. First thing I would do is stick a vacuum guage on it and see what that tells you.
Steve
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