intermittent high idle '93 Acura

Hi all.

Honda starts up with a perfect idle, but within 3 or 4 mins of heading down the road idle gets up to anywhere between 1800-2500rpm and has a habit of staying there for the whole trip. It's like the auto choke is jammed on. This started off as a rare occurance but is now happening pretty much all the time.

If I give it a thrash for a bit, I can sometimes have the idle speed settle down -until the next day.

There is an alloy rectangular dome shaped thing about 2 inches long located up near the air filter which definitely has something to do with it all. It has a vacuum hose and water inlet/outlet (I think) hoses. When this is hot to the touch I've got good idle, when it's cold I've got a bad high idle.

If I pull the vacuum hose off I get higher idle -so not a vacuum leak.

Is this dome thing blocked or could I have a water pump problem? Engine doesn't run hot so I don't know about water pump.

Thank you all for any help for this dummo.

try disconecting the IACV and see if the idle drops...

I don't think I've got one of those. I'm non fuel injected. It's definitely got something to do with that little manifold thing not getting hot. Any other ideas?