I have a 1998 Prelude Base. Whenever I start it up in the morning it idles from 600rpm to 1700rpm, it continues to go back in worth until the car reaches operating temperature. After reaching operating temperature the car idles perfectly fine. Does anyone have any ideas. I was thinking O2 sensor, but I unplugged the primary, then the secondary, but the car continued to distribute the same symptoms. I also replaced the MAP and I tried another ECM. I thought it had to be a sensor that needed to reach a certain temperature before it functioned. Well does anyone have any ideas.

 

Well here is some more troubleshooting info. I started the car up when it was cold, and it was sporadically idling as stated above. I disconnected the intake and placed my finger over the fast idle valve port, the car then started to idle properly. When I released my finger it idled sporadically again. This confused me because I thought the FIV was supposed to be fully open at startup(cold) which it was. I also tried pulling the IAC sensor harness off at startup(cold), this also caused the sporadic idle to dissappear. I thought the IAC was just for after warmup. Aren't there any experts here who can help a young troubleshooter?

 

The FITV just allows some air to bypass the throttle, raising the idle. I guess sometimes the guts of this can work loose & then this excess air is unsteady. Sounds like your problem?

The AICV (it's a valve, not a sensor) should be working all the time. But it's job is to steady the idle, not to raise it when cold.

Look for vacuum leaks, but I think they'll still give you a flaky idle even when it's warmed up.

Remove the FITV (drain some coolant so it doesn't make a mess). Tighten the insides if they're loose. Clean the airways?? Remove & clean the IACV. Make really sure there's no air in the cooling system.

Set the base idle. I don't know how much this varies, but it's something like this...
- Warm up the engine thoroughly - turn off all accessory loads.
- Unplug the IACV, use the throttle to keep it from stalling. Adjust the idle screw for a 450rpm idle. (If you're not careful it'll want to stall.)
- When you plug the IACV back in, it brings the idle back up to 800 or whatever.

 

like jim blake said adjust the fitv

 

I adjusted the idle properly now I'll try adjusting the FITV, and cleaning the IACV.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Yuleluder &raquo;</TD></TR><TR><TD CLASS="quote">I adjusted the idle properly now I'll try adjusting the FITV, and cleaning the IACV.</TD></TR></TABLE>If you adjusted the idle with an FITV that's dirty, flaky, or stuck open, then you didn't do it properly. You'll end up doing it again. That's why I said those things in that order...

 

The venturi style valve was loose, I was able to get about five turns on it. Now the car idles fine. Thanks for your help, much appreciated!!!