Idle revs up and down when engine is warm

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I just put Y8 intake manifold, head, fuel rail and other minor stuff, 93 p28 ecu, on my 92 dx block. Everything works great but the idle. at first it was revving all the time and loud hissing from the black metal box below the intake manifold by the block. I plugged a vaccum line going from the intake manifold top to where it meets the head and the hissing isnt as loud, also it is only revving now in Park and Neutral, also only after the engine has warmed up to operating temperature. There is no check engine light. It drives fine. I have a vafc ready to go in but I want to get the idle fixed 1st. any ideas what's wrong? another site said a air gap in the coolant line and i should bleed the system. Sounds valid since it happens when the car is warm. I wonder if it is a vaccum/emissions problem though?
it sounds like it could be a vacuum leak... did you scrape all the old gaskets off?? did you even get new gaskets??
While it's running - spray the hoses with carb cleaner or wd40. If the revs drop you've found your leak.
just watch out for fires.....


bubbles are a much safer alternative
Originally posted by pissedoffsol@Oct 15 2002, 01:02 AM
just watch out for fires.....


bubbles are a much safer alternative

And you probably didn't run with scissors either! :worthy:
Yea all the gaskets were replaced.... even when the car was running and the engine is hot, if i shut it off and start it again it will idle smooth for like 5 seconds, then hiss & rev. like its mad at me for giving it vtec.... maybe i'll change my name to pissedoffcivic :lol:
pull out and clean your idle air control valve located on the intake manifold
i noticed that when i was putting it on the y8 manifold, the screen had a bunch of black gunk on it, the same black gunk that is always inside throttle bodies & intake manifolds. ( i hope that stuff isnt there for a reason, cause i removed it all) I didnt clean that screen though. I will try that. Also, I am using my DX throttle body which i know has sensors in it that can effect idle. maybe since I have p28 ecu and Y8 head/intake manifold now I should replace the TB too?
When i took the AIC off to clean that screen, I think i may have found the problem!!!!!
the Y8 head as 1 less cooolant hose coming off the back, so i bought a T splitter at home depo and connected it through two other lines. Inside one of those 3 lines running together coolant is going to the Throttle Body, which then goes to the AIC. I'm guessing that there is hotter coolant going to it than there should be. perhaps one of the original lines was cooler than the other, and now they are mixing together cause of my home-depo T splitter. It only hunts for idle after the engine gets warm which makes me think this has to be it! What to do about having 1 less coolant hose coming of the head has me stumped though...