My brother has a 91 prelude with the b20 motor. It has a major idleing problem. When the car first starts up it jumps up and down the rpm's until it warms up. One mechanic said it was a bad radiator so I put a new radiator in. Then the cooling hose going from the motor to the tranny got a hole. Replaced that and still the idle is muffed. It jumps from like 400 or so to 1000 and back and forth. Does anybody have any idea what this could be? Thanks for any help.

 

it could be the fiav. i had a surge when while my engine was cold. i opened up the fiav and adjusted it and it went away. search for a walkthrough of this, there is one somwhere

 

thanks a million.

 

What kind of weirdo mechanic would look at the radiator for this type of problem...

 

I think he hooked up a scan tool and it read a cooling sensor problem. The radiator looked bad internally once I changed it, but the problem is still there.

 

If it's a cooling sensor problem, it's definitely the FITV (Fast Idle Thermo Valve). This valve (located underneath the throttle body) has coolant lines that run through it. When the coolant is cold, it opens the valve to let more air into the engine, thus you have your higher idles at cold startups. At high coolant temps, the valve closes, thus you have a more normal idle. It's definitely the FITV. I bet you.

When this part goes bad, idle surges exactly like you are describing. It is often the culprit for these symptoms. A close second is the IACV (Idle Air Control Valve), but it isn't in your case. Otherwise the idle would be fucked all the time.

 

Very helpful. I will check that out first thing in mthe morning.

 

Yeah, now you gotta tell me who the girl is in your avatar.

 

You can try to follow this write up from 92lude.com...although I wouldn't really recommend it, because the idiots on that ricer forum can't even label parts correctly...It's actually the FITV they're tampering with...not the IACV...but here it is. It will give you some idea of what you will be dealing with.

http://www.92lude.com/idle_air...d.htm

When my FITV went bad, I just went to honda to buy a new one. I dealer it up.

 

That's an ex-girl of mine that i still have benefits. Yeah she wants me to take it off of here but evytime i log on and post i want to call her up. She doesn't mind when I call though. LOL