I had low RPM (about 600 RPM) problems at lights.

I had low RPM (about 600 RPM) problems at lights and the car would shake. I took off the Throttle body and cleaned it, and also cleaned the MAF. It then ran very well for an hour and then suddenly at a red light the RPM was even lower than before (around 500 RPM). Took off the IAC motor and cleaned it and still have the same issue. I have tried checking for vacuum leaks but none are apparent. I have also purchased another IAC motor from the junk yard and this did not resolve my issue either. The RPM is sometimes under 500 RPM and you can feel the car struggle to get moving. Once moving however it operates normal (except it started burning up a lot of gas.)

More info: when the car is cold, the car idles at around 1100 RPM until it warms up and it goes down to a normal 800-850. It is after I start driving and then come to a stop that my idle becomes very low. It also is low if I turn the car on and the engine is still warm. If I throw it in neutral it will idle a little higher around 650-700 RPM. Please help!

Timing belt (along with water pump, seals and pulleys) were changed 10,000 miles ago (aisin kit) but the problem existed prior, so it cant be from that. Spark plugs were changed at the same time (denzo plugs). Alternator is brand new and so is the battery. Use synthetic oil every 3000 miles! I wish this car wouldn't run like this!

Any suggestions will be greatly appreciated.