Fluctuating Idle at warmup - Honda Prelude Forum

01sslude · 01-31-2009, 02:29 PM

Ok guys, I'm a new member of this site but, not forums in general. I did search thoroughly. No posts fit my exact situation. So here it is:

2001 Prelude base with 113k. No check engine lights.
During the warm up of the car, until temp gauge starts to rise to normal operating temp my idle will fluctuate from 1200-1600 rpms consistently. It is a very annoying sound. Once the car is warm this never happens. Any ideas?

Car runs perfectly other than this annoyance. Thanks in advance

new2prelude · 01-31-2009, 02:54 PM

i have the same problem with mine...i live in central illinois and when the temps get down to -5 degrees, my rpm's fluctuate until it warms up...my car runs fine, so i think it is the cold unless you live in warm weather then i have no idea...my dad's civic does it as well in the cold.

01sslude · 01-31-2009, 03:00 PM

I live in east tennessee and it does get moderately cold here but, it seems like something could fix this problem, some sensor maybe.

new2prelude · 01-31-2009, 03:04 PM

yeah, you are probably right, good luck with that, i will be watching this post to see if i can fix mine haha

sexylude97 · 01-31-2009, 03:55 PM

fast idle thermo valve $80 (under throttle body)

or

Idle air control valve $200 (valve on front of intake manifold)

to see if it is the thermo valve
1 - remove the intake pipe from your throttle body.
2 - start you car and let it heat up to operating temp.
3 - while it is warming up there is a hole inside to the lower rear inside your throttle body feel that hole and make sure air is being sucked through it. if not change the valve
4- Then hold the rpms @3000 until the radiator fan comes on twice then let idle.
5- go put your finger to plug the hole, if the idle of the engine drops valve is bad.

01sslude · 01-31-2009, 04:06 PM

Ok I'll try that. It seems more logical that it would be the fast thermo idle valve since it's fine when it's warm. What is the primary function of that valve?

sexylude97 · 01-31-2009, 04:27 PM

ya, but on my accord it was the idle air control valve..... so ya never know.

01sslude · 02-01-2009, 07:00 AM

I also noticed that it will jump up when you first start it even if it's still warm. but only for one or two times. It seems like it is getting increasingly worse.

sexylude97 · 02-01-2009, 09:03 AM

the valve has to sense once you start the car.... you don't think it cools in between starts and has to identify the temp all over again?

01sslude · 02-01-2009, 10:11 AM

I'm sorry I am not sure of what you're asking?

sexylude97 · 02-01-2009, 10:44 AM

just test the valve......

01sslude · 02-01-2009, 10:48 AM

I just called the local Advance Auto, and they couldn't find a part under that name. Could it be referred to as something else? He found the IAC valve but, not fast idle thermo valve.

sexylude97 · 02-01-2009, 11:37 AM

did you test the valve?

01sslude · 02-01-2009, 01:06 PM

Yeah it's faulty. So where can I get this part at?

sexylude97 · 02-01-2009, 01:22 PM

honda

try these guys. I always get parts quick and cheap. part #12

https://www.bkhondaparts.com/billkay...hidIrno=%7C012

01sslude · 02-01-2009, 01:46 PM

Thank you. Do you think autozone or advance would carry it for any cheaper. Also, I might try to clean it before buying a new one just in case.

sexylude97 · 02-01-2009, 02:38 PM

i think it is a special order from autozone. thats why i ordered it. good luck

01sslude · 02-03-2009, 09:14 AM

UPDATE: So yesterday i was driving and the check engine light came on. Suddenly I noticed the idle being kind of rough in the low rpms of first and second gear. Car felt kind of jerky. I had advance auto put it on their diagnostic tool. It had two Idle systems malfunction codes. The guy said it's probably the IACV instead of the Fast Idle. What is the difference?

Solid · 02-03-2009, 09:23 AM

Do you have the codes that were thrown?

01sslude · 02-03-2009, 10:04 AM

I don't have the exact codes but, go back and find out. Also, Could it be the TPS causing this problem?