I want to start by referencing someone else's post because it sounds so similar (I'll add it to the end). Namely, somewhat rough shaky idle when stopped, in drive, when the AC kicks on, and the RPM drops to what looks like around 600. This doesn't seem noticeably dependent on the weather or how long the car has been running that day, though maybe I notice it less (or just ignore it more) after driving a while. I finally took the cover off the motor, only because it's clips have gotten worn and old, so when the shaking starts its the first thing I notice. The car has fairly low mileage for a 2009 (125K) , and all the coils and plugs were changed last year, only because it was well past 100K when it had been recommended for a while. I'm going to bring it in for oil change soon so of course I'll ask for a full diagnostic. But are there any things I can do? Are injector cleaner addatives a waste of money? I realize the engine idle speed is all computer controlled in modern engines, but is there any adjustment like older cars had to further compensate when the AC compressor engages? The car runs really well, and I've never seen even a hint of trouble driving at regular speeds. And one thing I know for sure is that an expensive repair is something I really could ill afford right now.

Here's the other person's thread I was referencing. Their milage was much higher, but the problem sounds the same, and there was never a fix reported. https://www.scionlife.com/forums/sci...m_content=post

EDIT: Got some advice and saw a video on youtube suggesting cleaning my throttle body. Don't know if it will solve the problem yet but I did it, and it definitely needed to be done! And just as the video I saw on it advised, if expect the idle to be higher for a while after removing a lot of build up. There definitely was, and the idel is now higher than it should be. So I'll repost in a week or so to see if things settle out. I'll also have diags done when I get the oil changed, so I'll know I'll find out if there were any codes that are all clear now!

 

Hey Peter Pan:

I had a slight rough idle problem, which is usually a combination of possibilities.

From what I understand, a good place to start is exactly where you started, cleaning the throttle body, but that's only half. Did you clean the MAF sensor as well?

The MAF sensor is critical in detecting how much air and fuel in combination is needed, and a dirty MAF could be not work.

If you did your throttle body, you have already done the disassembly to get to the MAF sensor.

You will need MAF sensor cleaner designed specifically not to damage it, it is a tiny, small wire basically. You have to remove the sensor and housing to safely clean it.

Video:

 

I've tried to work on this and what helped was of course cleaning the throttle body. You have to separate it from the engine so you can clean the back as well just make sure not to take out the coolant lines from it unless you want to flush the coolant which is not a bad idea to be honest. You might as well replace it's gasket since you are at it. Clean the MAF sensor as mentioned, I have not checked the fuel injector but I haven't done that to my car. What's interesting is that when you are stopped on traffic and turn on the parking lights the RPM increase a bit and will elimate the dip in RPMs. Try it on a red light with the radio off and listen to the change. Also a very good idea is to take your car on a highway and maintain speeds of 70 ish for like 20 minutes. This will clear out a lot of carbon if there's any even in the Catalityc converter. Just make sure your car is warm enough at regular speeds before doing it. Do it once a week depending on how often you drive at highway speeds.