Gallant 2001 2.4L drives rough

Dear gurus,

I recently purchased a Mitsubishi gallant 2001 and had a high idle rpm on it like 1500
to 1800, My brother being a car enthusiast informed me that we have to clean the
throttle body coz it will help the idle settle to normal. So we purchased a carburetor
tune up conditioner spray and sprayed the throttle body with it. All the carbon deposits
melted from it and I could see the golden flap. I also had a problem with the one of the
coils at it used to pop out sometimes and the car went rough but I had it fixed into its
hole from one of the mechanics. Everything was going good until two weeks ago when
the car started messing up at Idle and when I hit the gas. It was not picking up
acceleration and was rough even in the second and third gear. So I replaced the spark
plugs with new genuine ones. But the problem is still there with excessive vibration.
Another little concern is flashing of check engine light for a 0.5-1 second when I start
the car. The temperature gauge is at normal, I check the water level and engine oil after
a day or two.

Please help !

Thanks