Thanks for the reply fish! After driving the car for 2 weeks now, the low rpm issue when starting the engine cold has recently gone away. For the past 2 days now, the car started up easily and normally like it did all these years in the morning at ~1600 rpm instead at ~900 rpm. I believe the ECM finally adjusted itself?
But let me give you a little more detail as to why I clean the MAF sensor and the throttle body in the first place...
The car is a 2001 Toyota Corolla LE automatic with 94,5XX miles. The car was purchased new and it has been super dependable. In the 16 years that I own it, I never had to do any repair, just basic maintenance item (fluid change, brake pad, new tires, etc.). But lately, the engine has developed a mild vibrating/shaking issue when you stop at a red light or a stop sign. The vibration from the engine would cause the radiator to vibrate and rattle against the frame. Upon inspection, I discovered the two radiator upper bracket is shot. The rubber is all dry and crack. It no longer hold the radiator in place securely. I replaced the two old one with two new one (part #165330D010). With the two new upper bracket installed, the radiator rattling noise cause by the engine vibration has decrease a lot but it is still there.
In an attempt to solve the vibration problem, I did some googling and watched a youtube video by chasiu75 on how to clean the MAF sensor. Since the MAF sensor on my car was never clean before, the amber color part of the sensor was dirty. I cleaned it with CRC MAF Sensor cleaner. After the MAF cleaning, the car seems to run a little smoother and the vibration seems to be reduce by a little at idle.
Wanting more, the next thing I did was to clean the throttle body since it was never clean before. I use CRC throttle body cleaner along with a rag and a toothbrush to clean it. Again, I watched a youtube video on how to clean it. After the cleaning, the car won't start (spray too much and flooded the cylinder). I had to put the gas pedal to the floor and crank it a few time to finally start the car. The engine was running rough for a few minutes before finally smoothing itself out. I added a bottle of Chevron Techron Fuel Treatment, filled up the tank with gas and went out for a 30 min drive thinking that would let the ECM adjust itself. The next morning when I start the car is when I notice the engine rpm is way lower than it used to be when the engine is cold hence the original topic that I made here on this forum.
Fast forward to today, the low rpm issue when starting the engine cold in the morning has gone away but the engine vibration at idle has not. The engine idle vibration has become somewhat sporadic in nature now. Sometimes it would be smooth stop at a red light and sometimes it would vibrate causing the radiator to rattle.
The next thing I am planning to do is to change the valve cover gasket (#112130D040) and seal (#9021006013), pcv valve (#1220422051), and the spark plugs (SK16R11) since they all have never been change before. The parts should be arriving sometime next week.