Hi guys!

I am having a strange problem with my is200 lately. When i start the engine on cold start, it starts as if someone pressed the pedal a little bit and rev high (normal as i understand it needs to each the operating temp). When it reaches the operating temp the idle goes to its normal position and its fine, as i turn on the AC, its fan kicks in which is normal, usually when it kicks in it cools the engine, and i see the temp going down. Now when it reaches a certain point lets say 1/4, the rpm rises slowly and goes above 1000rpm. When i tun off the AC, the rpm rises more may be 1300rpm, then as the temp rises it slowly goes back below 1000 rpm. This was not the case previously. Before, After the engine is warmed up, when i turn on the AC and temp cause down, the rpm never rose above 1000rpm. I have checked for vacuum leaks by spraying a caburator cleaner, there was none. checked all plugs and coils and they are all good. Right now is like a battle between the ECU wanting to reach the operating temperature as the AC fan is cooling the engine.

I had a mechanic who told me its a thermostat going bad. I want to believe him, but i never had this problem before where after the engine being warmed up and then cooled by AC fans the rpm goes up trying to force the engine to reach its operating temp.

Can you guys help me out on what to check? Where i live, we dont have reliable mechanics, they will get you buying different parts and still the fault remains. BTW, there is no CEL since i am having this issue and i have dove for about 100+ miles.

The fuel consumption is also affected since having this problem.

Following is the diagnosis data if needed:
Ignition Timing advance 8.0
Intake air temp 125 F
Absolute throttle position sensor12.9%
o2 sensor voltage bank 1 0.56 vlts
Short term fuel associated to bank 1 sensor 1 5.5%
o2 bank 1 sensor 2 0.010
short tem fuel associated to bank1 sensor 99.2%
Fuel system status 1 closed loop (using all o2 sensor)
fuel system status 2 closed loop (using all o2 sensos)
coolant temp 201F
short term fuel bank 3.9%
Long term fuel trim bank 1 3.9%
short term fuel bank 2 3.1%
Long term fuel trim bank 2 -7%

Data taken while idling after a drive

 

Just an update in case someone encounters the same issue as mine, it was Thermostat.

 

Hey man, now years later I want to thank you that you updated the fix you made. I changed to a new thermostat and started to have high idling. Turns out my new thermostat (not original) was bad, it keeps staying open. I will put the old one back when the new seal arrives.

Do you still have the car?