97 Nissan 200sx 2.0l....car wont stay running when put in gear. When idling sometimes when engine is reved up it stalls, other times while idling I can rev it up and its smooth but once I put it in gear it stalls, also oil inside distributor cap.

Check your intake tube for a leak , if you unplug the Maf and then start it does it stall when you put it in gear ?

Oil in the distributor will do that. But why is oil getting in there? The positive crankcase ventilation(PCV valve) should prevent this. Plus the should be one seal on the distributor and /or cam. I would pull the distributor and check for sloppiness. Also check for the cap seal. Oil could be from the valve cover.

There should be no oil in the distributor. Replace it. Oil will cause the spark to go anywhere. Most likely to a ground. The distributor base.

fuel filter

fuel FILTER or fuel lines?

Best Manuals here's link to get you solution for the problem in your vehicle

First thing, put the transmission in park, start the engine, with the engine at idle, check the fluid level with the dipstick. If it's low, add fluid and try it again.
If it still doesn't move and your are sure that it is full of fluid, then you most likely have an internal tyranny problem that would require an overhaul. have a good day !!

We have two Nissan 200sx's, a 1995 manual and a 1996 auto. Both had this problem and both turned out to be the same thing. The "idle air control valve." It was most noticeable if you ran the air conditioner and then came up to a red light. You would have to keep pushing on the brake and race the engine a little to keep it from shutting off. Replaced that part and both cars have never had the problem again.

Sounds like leak in high pressure side of turbo to inlet manifold tube.
Results in gutless or no performance but idle & revving in neutral ok.
Check for splits or loosened joints.

IAC valve problem. Nissan has a updated harness (with one way diode inside of the harness) to prevent backfeeding for the IAC valve and a new IAC valve also gets installed. That's where I would look. IAC valve or "idle air control" valve.