Its not on my 4runner, but on my friends car (Honda).
When it starts up its fine (1200 RPMS to warm up), in drive its fine (800 RPM's constant) but the moment you put it in park before you shut it off it goes between 1100 and 500 and almost feels like it is surging. If this would be a vaccuum leak, wouldn't it be in drive while stopped at a light too?

What are some possible things to check for?

Thanks guys, I come here for all my mechanical problems

 

Can anyone give me some insight?

 

Have him check to make sure his timing is set correctly for starters. That sounds like the timing isn't right, or the throttle position sensor isn't operating or set correctly. Otherwise typically a vacuum leak will be evident all the time, not just at idle.

 

Idle air control valve.

 

I agree there. I would check the tps. If it is right on the edge of being set right, it will jump around like that

 

I have the same problem occasionally. a search for "idle air control valve" on parts websites yields nadda for me. does it also have another name or I am just completely failing to find it?

 

It would help if you told us what vehicle your trying to find it for. I went to partsamerica.com and searched for a idle air control valve for a 95 Civic and it pulled up the part no problem.

 

Sorry I really ought to put my vehicle info in my sig line
it's a 1990 4Runner 3VZE Auto.
I tried partsamerica and didn't get anything

 

Idle Speed Control (ISC)

Partsamerica doesnt have it

Couldnt find it on any parts sites.

I do have one for sale off my 88 V6 if your interested. PM me.