I've got an 88 4runner 3vze automatic that recently developed a very strange idle issue after fixing a leaky water pump. It will start up fine and idle about 1500 then when driving for the first ten minutes or so when I let off the gas the rpms will drop to but then surge a few times before leveling out, as I said this goes away after about ten minutes, then when I put it in park it will shoot back up to 1700 rpms and surge between 15 & 1; however if I go back to it and start it back up within the next two hours it will idle perfectly at 900. I know I've got a phantom bubble in my cooling system that I've I'm having a hell of a time getting rid of but it seems to consistent to be a bubble, any ideas? I can post a video of the surging later. Thanks.

 

It sounds like your truck only does this when cold. How much RTV did you use on the pump? The reason I ask is this-


I had a similar issue on my 22RE. I found a random youtube post about the idle air control valve coolant routing pipe being clogged with RTV. On my motor, this is the small pipe on the thermostat housing with a 90 degree elbow. I was going to remove my IACV to clean it anyway so I thought I would check. This is what I found:





Low and behold, the line was clogged with RTV! This was preventing coolant from circulating to the IACV and allowing the valve to do its job and properly control the idle when the engine was cold.