car idles low in park and neutral?
 

2001 Mazda 626 4cyl auto

I recently replaced my valve cover gasket (it was a little leaky.) The car ran seemingly fine before this. While changing the gasket I noticed one of the spark plug holes had oil in it (Not sure if this is relevant.) After I changed the gasket, the car seemed to run fine then i noticed that in neutral and in park the idle would dip super low. It kind of feels like it's fighting off stalling almost. The next day, I bought new spark plugs and replaced them. I drove the car to normal operating temp and tested it in neutral and park and even stopped but with the A/C on and it didn't idle low anymore, so I thought it was fixed. Well, the next time I drove it, it started doing the same thing again. So now every time I am in park, neutral, or even drive if I'm stopped and have the A/C or fan on it idles really low. I have a squeaky belt I'm getting replaced this weekend but it was squeaking before I even changed the gasket and I didn't have this problem. Any idea what the problem is? I am not really a car person and can only do very basic things.

Thanks in advance

Double check your PCV valve, hose and any other vacuum hoses that you may have disturbed, an air leak if big enough will cause the car to stall, to help locate the leak VERY VERY carefully and VERY sparingly spray starting fluid in short bursts around the vacuum lines, any leak found will result in the engine RPMs going up briefly. The other thing it could be is a faulty/plugged IAC valve, this controls your idle RPM, when you turn on the AC the computer should tell the IAC to open more to raise the idle due to the load of the AC, if its not working then your idle will not bump up and the car will threaten to stall.