Idle Speed Too Low

[lexus082]

After I had my starter replaced I had a low idle speed and the car was shaking slightly. My check engine light was on and I needed to replace the TPS sensor. The Toyota service advisor said the low idle speed and shaking was probably due to the TPS sensor going bad. So I bought a new TPS sensor. After installing the sensor my idle speed was around 1000 rpms. I took the car back to Toyota and the mechanic wasn't sure why it was idling high. Then, I took the car to the Lexus dealer and they told me I needed a new throttle body. Also, the engine wouldn't idle down going from cold-warm. The idle stayed steady at 1000 rpms even after it warmed up. So I bought a used throttle body which included the TPS sensors, etc.

Today, I swapped out my throttle body with the used one i bought. So I started the engine and it wasn't idling as high as it was before. Then after a couple minutes the idle started to drop as it was warming up. The only bad thing was the idle went down too low and its at 400-500 rpms and now the car is shaking again. So now its doing the same exact thing as when I first got it back from Toyota after they replaced the starter. I don't know if its the computer that adjusts and makes the idle speed go up to a 1,000 rpms? I will be closely monitoring what happens over the next few days if the idle speed changes or if the computer seems to make any adjustments.

[lexus082]

I talked to the ups mechanic at work and he said to check/clean the IACV. He explained to me that if it was gunked up it wouldn't allow as much air to pass through it, therefore causing the low idle speed. And then if the valve was working as it should it may not thow a CEL. So its believed that if I clean the valve it may open up the air passage way a little more which would allow more air in and then the computer would increase fuel, which in turn would increase the idle speed. Hopefully up to the normal idle speed

[lexus082]

I cleaned my IACV and thats not it. I still have a very low idle causing the car to shake. Idle speed once warmed up, seems to be around 200-300 rpms.

[Slender]

@lexus082 Did you ever figure out what was causing the poor idle?