HELP! I barely came home on a miracle on this one tonight because after running a few minutes on the freeway, when all of a sudden I noticed my temp guage spike past halfway then down to one quarter of the way when I got off the freeway. Then, steam just started coming from my engine bay. When I pulled over to check it out, I see steam coming the intake manifd/egr area. I couldnt pinpoint the problem because it was dark as f#¢k and I had the turn off my engine to prevent further damage. When all was said and done, I saw moisture all over my intake manifold, intake, etc. Radiator is still in one piece, but wth?

Side note: High idle when cold start, then idle fluctuates up and down for a few minutes, but stops when engine is warmed up...

 

It might help to know what kind of car we're dealing with.

 

Its most likely either something to do with your heater core hoses or your FITV hoses. I had the exact same issue last night when my inlet-valve hose broke, did some research. When the temp sensors aren't being completely surrounded by coolant the show false readings. The fluctuation in your idle is also because the FITV is purging air into your intake and then closing, once the car warms up it completely closes and your IACV kicks in to hold your idle. Just replace all the hoses for the FITV take it off the TB, clean the hell out of it, and inspect the core hoses for leaks.

 

Sorry about that. Its a 91 Honda Accord EX. And thank you, NZXTInerTia, I will check that out ASAP

 

I had a problem just like that. Turns out it was the heater hose under the dizzy. The dizzy o ring was leaking (and i knew it) right on top of the hose caused it to swell then break and hot coolant on a hot block/head caused flash vapor. So check the hoses like nzx said and replace the dizzy o ring


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Problem solved. Had a friend do a cooling line pressure check and saw air come out of a busted HEATER HOSE that was underneath the air intake and throttle body. It was b!#¢h to get to, but at least its up n runnin again!

Thanks to all the responses, you all rock!