I've got a '97 4Runner with roughly 200,000 miles on it. I've been having trouble with a high idle. It starts out around 1200 rpm in the morning but after running it for about 15-20 minutes when i shift to neutral or park it will go up to 1500-1800 rpm. I had no check engine light on. When I unplug the IACV it idles down to 1000 rpm and it runs fine. It also puts up the CEL. I thought the IACV was the culprit so I replaced it with a used one from eBay and now it's still doing the same thing.

Has anyone run into this before? I would assume, because it runs fine without the IACV plugged in, that I don't have a vacuum leak?

Thanks for any help