This started out of the blue a few months ago. Didn’t do it one day but did the next kind of thing. In gear and stopped, the truck has always idled about 750-800 RPM’s. It still does for about the first 10 seconds after stopping, but then kicks down another notch after those 10 seconds of sitting to about 675-700 RPM’s where it stays until you proceed. This RPM puts it right into the 4 cyl. shake zone that even balance shafts can’t help. It’s now doing this all of the time after coming to a stop with the truck in gear. Any RPM's above that (like when the A/C kicks on) feels normal again.

After looking here and other sources, I came to the conclusion that the likely source was the idle control valve (ICV). I took it off and cleaned it well (wasn’t really that dirty), replaced the sealing O-ring/gasket, and cleaned the throttle body and MAF sensor while I was at it. Put it all back together and it idled at higher than usual RPM’s at first, so I really didn’t know if it was successful right off. However, the next day it was back to acting the same way as before. I see there are many sensors and connections on and around the ICV, so it could still be bad. Then you have multiple sensors in the exhaust system and what looks like a vacuum-controlled idle stop on the throttle body which I assume all could affect mixture settings and idle. Haven’t found any leaking vacuum hoses either.

The truck has 162K miles on the clock. Plugs and filters are all good, and the injectors and coils haven’t shown any signs of giving up yet. Any other suggestions on what it could be and/or what else to check?

 

My '03 2.7L AT does the same thing and I consider it normal. Last year when the exhaust valves burned on cylinder 3, the prolonged idle 650rpm shake was much more pronounced...shook the truck enough to rattle the gas tank door.

Scanner showed normal readings right up until P0303 misfire code started setting the check engine light, very difficult to diagnose until I did a compression test and cylinder 3 was only making 80-90 psi.

Have you checked valve clearances yet? It's on the 90K-mile maintenance list and not something you want to let slip past you, very expensive to fix.

 

Thanks for the reply!
Valve clearances were checked at around 100K. This doesn't act like a compression loss, and all cylinders still show numbers in the good range. It reminds more of a vacuum leak. It's not throwing any codes (even passed a recent smog test) and runs great except for the idle speed issue. I can't consider it normal since it didn't do this for the first 12 years we had the truck. It's just figuring it out. Maybe will try an independent Toyota shop that was recommended to me to see if they can pinpoint the issue.

 

I'd be really interested in your findings.