Surging rpm.... - Honda Prelude Forum

supersano · 10-23-2006, 10:03 PM

Hello everyone,
I've been having some problems with my engine when it starts up. When I start it up in the morning the rpm revs up and down until my engine warms up then it stops. Can someone please diagnose the problem, so I can get it fixed.
Thanks in advance.

dohcpower v2.0 · 10-23-2006, 10:19 PM

either your fast idle valve or IAC valve.....

Fast Idle valve is under the throttle body, the IAC is bolted to the front side of the intake manifold.

supersano · 10-24-2006, 09:34 AM

Do I need to replace them?

Kap TypeSH · 10-24-2006, 09:35 AM

+1 on the IAC

BBYlude · 10-24-2006, 11:10 AM

test them, info for doing so should be in your helms manual, if they're bad, replace them

marcucci · 10-24-2006, 11:12 AM

Also check your coolant level- low coolant or air in the system will produce the same result.

The TB/IACV coolant loop bypass will do this too (if it was bypassed).

supersano · 10-24-2006, 10:01 PM

Thanks for the input you all. I was thinking that it was the coolant level. I left the cap opened for about 15 minutes and there was no bubbles coming out. I guess it's time to replace the IAC. Thanks again.

UBLOSIN '98 · 10-25-2006, 12:45 AM

ok this is probably gonna sound dumb, but i've been wrapping my brain around it and can't figure it out.... what's an IAC?

Kap TypeSH · 10-25-2006, 07:09 AM

Idle Air Control valve.

Glaucus · 10-25-2006, 03:44 PM

Mine's at the shop for the exact same problem. The car throws no codes, so the shop suspects it's the Fast Idle Valve. They consulted Honda and Honda says in the absense of codes, it's likely the FIV, and they replace a lot of those. I ordered the part, won't be in until Friday or Monday. I'll report back with results.

- Mike

blackludebosh · 10-28-2006, 01:29 AM

I have been having the same problem, on cold boot ups my car revs by itself from 1.5 to 2 rpm and stops after the engine was warmed up. Any idea on the cost to fix this?

Glaucus · 10-31-2006, 02:53 PM

Well, I had it the shop. They suspected the fast idle valve and ordered the part. The mechanic noticed I was low on coolant so topped it off. Hasn't happened yet, and I'm thinking I might skip the install of the new FIV. So check your coolant!

- Mike