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I've got a 1990 prelude and I ended up doing an oil change, after completing the oil change it hasn't been leaking and the oil looks fine so I think its unrelated to my problem but it might be if anyone has insight. I also disconnected the spark plugs and plugged them back just to blow debris out of the spark holes, but the car still runs fine and doesn't misfire so it's not that either.

After doing the oil change I fired the car up and the engine light came on, the car runs and drives the exact same but I noticed the idle stays around 1500 but I'm pretty sure it's always done that.

I checked underneath the carpet flap for the flashing red light and it flashes 6 times then pauses and repeats. I have absolutely no idea whats going on. The only info I was able to find online is that it means that the coolant temperature sensor is having problems but my temp gauge is working perfectly fine and everything else is.

I have a 1990 3g with a B20A5 (2.0l DOHC) engine in it.
 

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As I thought, 6 flashes is a cooling temperature warning. Most likely the Fast Idle Control Valve is stuck, or plugged. Needs to be removed and/or cleaned/replaced. This device tells the computer when the engine is warmed up or too hot, turns on the cooling fans and also controls warm up idle. If air is in the valve or its plugged water cannot be detected telling the sensors what its status is. This will also cause the idle to bump up and down repeatedly.

First off though, CHECK YOUR WATER LEVEL IN RADIATOR.
 

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Code #6 is specifically the Engine Coolant Temperature Sensor, also known as the TW sensor in the factory manuals. You need to test the sensor, which is screwed into the cylinder head on the front right corner, near the TDC sensor. First, make certain that the coolant is full. Run the engine until it is at normal operating temperature. Shut off the engine, remove the connector, and test the resistance between the two terminals on the sensor. It should be between 200 and 400 Ohms. If not, replace it. If so, make sure that the contacts are all clean and making good connection. Clear the trouble code and test drive. If the code returns, you'll need to start testing the wiring between the ECU and the sensor.
 
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