Idle issue

[emarald]

I have a camry 94 model with the 5sfe 2.2 motor. When i bought the car 6 months ago the idling was at 1200rpm, i then replaced the throttle body with a second hand unit about 3 months ago and everything was fine. Then last month i replaced the thermostat due to the car taking long to warm up. Fuel efficiency and warm up time have both improved, but in the last 2 weeks my car has a tendency to just switch off. This happens after extended bumber to bumber riding and only when the car is idling. Switching on the aircon(rpm goes to 1100) seems to prevent this. Normal idling is at 800 accompanied with a small amount of vibration. Sometimes it will start immediatly, or otherwise it will only do so after about 10 mins. HELP

[RIP]

First thought would be to clean or replace the idle air control valve. Second would be to inspect and test the EGR system. There are many possibilities.