I recently bought a 2000 Mazda Protege LX 5 speed with a 1.6L.

I changed the timing belt, water pump, seals, thermostat, radiator hoses, spark plugs, coil on plug boots.

After start up the car idled about 1200 rpm cold and then once warmed would fluctuate between 100 rpm and 800 rpm until stalling.

To start with the cheapest troubleshooting tactics I did the following:
1) Verified there were no air bubbles in coolant system. Basically I watched the bubbles go into the overflow tank but there really wasn't much more I could do.
2) Replaced throttle body gasket
3) Replaced injection port O-rings (4 total)
4) Replaced Intake manifold gasket
5) Checked for cracks in Intake hose
6) Checked resistance at Intake control valve and throttle body sensor.

The resistance of the throttle body sensor was within range according to the service manual.

The resistance of the intake control valve was on the highest side of the recommended reading in the service manual. I didn't want to replace a $250 part until I exhausted the inexpensive potential problems.

Well the car still fluctuates at idle then stalls so I'm going to have to bite the bullet and replace the IAC valve. I just hope this fixes the problem.

 

Update: A an hour later I decided to pull the electrical attachment to the IAC valve to see if it was working. When I pulled it before the car was started the car wouldn't start. When I pulled it when the car was idling it died. So I think the IAC valve is working.

I did pull the electrical connection to the Purge Control Valve when the car was idling and nothing happened. I took the valve off and sprayed some carburetor cleaner down each port and reinstalled.

I reset the computer using my OBDII pocketscanner and will drive around to let the computer relearn the settings.

I really don't want to start throwing money at the issue until I know for certain. I probably will buy a new purge control valve if the car keeps idling rough and stalling.