Funny Idle...
 

when I drive and shift through no problems. When I go neutral, car goes back and forth between 1k and about 500rpm's. What could it be?

Could well be the carb jetting is a little on the lean side. Since you didn't specify otherwise, either in this post or in your signature, I assume you're driving a 1968 Volkswagen Karmann Ghia. The solex 32-PICT carburetters in those are extremely sensitive to idle jetting in warm weather, particularly if you still have the "stovepipe" connector in place from the exhaust manifold.

check your spark plugs for dark oily coating. 2-stroke engines tend to foul out the plugs if you run too much oil in the mix. Also make sure your rotor button is clean.

well, to be exact and specific i'm driving a 2001 miata..no boost.

I may need an oil change but I know the right amount is currently in there.

my first thought is a sensor. idling or throttle position maybe?

and what is a rotor button?

I'm going to suggest going to your nearest autoparts store and purchase a can of "Mass Airflow Sensor Cleaner" (Ask for it, they'll have a can). Remove your Mass Airflow Sensor and spray liberal amounts of cleaner onto the element. Reinstall and report back to us.

What codes are you getting?

And identify your ride in your sig, so next time we don't have to ask what you're driving. (Help us help you)

I now have a whole new set of problems. They may or not be related to the idling problem. As I was driving home, I found that slowing down to 0mph would cause my oil pressure gauge to drop all the way and jump right back up.

Ran my codes. 4 came up

1. camshaft position Actuator A Bank 1 timing over retard
2.02 sensor bank 1 sensor 2 low circuit
3. 02 sensor bank 1 sensor 1 no sensory
4. manufacturer fuel air metering is off.

after reading a bit I find the IAC ay be to cause for some ofwhat is wrong. where is it located and how do I go about fixing it?