Low Idle / Stalling & High Idle

I have been troubleshooting an issue on my 2000 Prerunner for some time. At first I replaced the IAC valve(not OEM) after cleaning it failed to do anything(codes indicated failure). I have cleaned and eventually replaced the MAF,(codes indicated replacement) replaced almost all the vacuum lines (more on that in a minute), replaced the TPS, Seafoamed, hugged, and romanced this girl and still the problem persists. I am at a loss.

The problem: The truck starts up fine and will drive for a while. Once the truck gets significantly warm the idle will start dropping from 1k RPM to 2-300. The idle will stay at 300 while at an idle unless I do some hard driving then doing hard driving will cause the engine to idle high at about 1k. Then when I get to a light the idle will eventually drop. While the idle is revving high if I put the truck in park or neutral the truck with rev extra high, between 1500-2000 RPMs. Then it will eventually drop. The truck will stall out in parking lots, low speed moving the wheel.

It sounds like a vacuum leak, so I start tracing the hoses. Hitting the hoses with carb cleaner and I cannot find any idle change. So I decide to replace all the vacuum lines I can find. I thought I got them all until yesterday when I did a seafoam experiment and found smoke coming from the passenger side during the seafoaming. I found two additional vacuum nipples behind the engine that connect to the IAC valve. Replaced those vacuum hoses as well.

Does anyone know where I can find a schematic of all the vacuum hoses? I don't want to miss any more. Is there a vacuum hose on the power steering pump?

Anyone have any thoughts on this problem, what it could be or what it sounds like?

 

I had this on my 2003 4 cyl Tacoma and I discovered that the throttle body was worn at the throttle shaft pivots... the blade would stop at a different idle position every time the throttle closed. Cleaning it made it worse, all of the crap that had built up around the bore actually closed up part of the blade/bore clearance. A wrecking yard throttle body solved this problem, original had 375k miles on it.

 

I'm thinking EGR valve switching but I could be wrong. Good luck

 

Galisman how were you able to diagnose that problem? Trial and error? I assume you need to take the throttle body off but were you able to see the problem?

Steves, are you thinking the vacuum switching valve or is that another valve you were thinking of?

 

I know on an old truck of mine it was the egr valve itself (not sure if the switching valve and egr are one and the same, off hand) Mine was frozen open or closed (one or the other) and would stall the bitch out. Edit: The fuel pump relay failed and needed to be replaced around the same time but again may be nothing to do with your trucks problem. Good luck, Man

 

I ended up pulling and pushing on the throttle shaft to see how much inline play there was and comparing it to a buddys. I managed to find a used one in a wrecking yard for $50 and that fixed the problem.