I got my car back from the shop after a complete rebuild, and it runs very well now. However, after some miles of driving, the Check Engine light lit up. Together with the light, other syptoms include the radiator fan turning on full speed a few seconds after startup, and it stays on for about 5-7 mins after shut down. Also, start up when engine is cold is rough, and takes 10-15 seconds to smoothen out, almost as if mixture is not rich enough for cold starts. Car starts up and runs perfectly well when warm.

My guess is that the ECT sensor is bad and is sending a signal to the ECU that the engine is hot, hence the poor start up on cold, and overzealous radiator fan.

Am I correct? Thanks guys.
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...and the bricks keep on rolling