Mattimus

Hi all

I'm another prelude owner who has had to deal with the fluctuating idle problem. I own a 92 Prelude Si 4WS and was reading a post here with several fixes to it for the annoying idle. I was attempting to remove the FITV on the throttle body when i noticed the coolant hose that connects the thermostat to underneath the throttle body had a crack in it and was leaking coolant. So i thought maybe that was the reason for the idle problem? air bubbles getting into the coolant and throwing off the sensors so the ECU was forever changing the air/fuel to compensate? well i fixed that problem yesterday with a new hose and it hasn't been surging yet (I'm not sure it actually fixed it because it seemed to have stopped BEFORE i changed the hose during the day) and after i changed the hose i was trying to get the idle around the 800rpm mark. But the idle adjust screw on the top of the throttle body has been tightened all the way in and the idle still sits at 1000-1100rpm. I read somewhere someone mentioned getting under the throttle body and remove a small plate and adjust a plastic screw to adjust the idle but in the manual it only mentions the screw on the top? :S

Can anybody shed some light on this? Is there any other way of lowering the idle?

iidieiv619

-Did you bleed the coolant lines of any air bubbles using the bleeder?
-Try detaching the IACV off throttle body and cleaning the small filter inside?
(If you cleaned it and problem still exist, buy a NEW/or cleaned and tested IACV. My brother and I both had the same problem and we both changed the IACV and its fixed. I bought mines from eBay.)
-Also check your timing
-Check the Distributor Cap and Rotor. Make sure the metal contacts arent worn. If they are, replace.

There are many cases of the "Idle Problem" in Honda Preludes. Keep searching around.

LogicGate

Coolant lines only help warm up the air flowing through the IAC and FITV. They do not affect the mechanical properties of both devices. Do not mess with the IDLE screw, leave it alone unless car idles very low.

Follow the FSM for resetting the ECU:
0. Warm up car before doing procedure.
1. Remove 10amp fuse for 10 sec, then re-install
2. Disconnect IAC wire
3. Turn car on and idle for a seconds on 1,000rps and slowly let it go.
4. Verify IDLE is at 500rpms, if not then adjust IDLE screw (but I recommend that DON'T TOUCH IT lol)
5. Let it IDLE for 5 min. then turn off car.
6. Plug IAC back and turn car.
7. Let it IDLE for 10 to 15 min and make sure you do not touch the peddal. Just let it idle.

Mattimus

Thanks for the replies guy. Will try these and post back. I have already reset the ECU but haven't done that full procedure when I did. Also, does anybody know about this other so-called idle screw 'under' the throttle body??

Mattimus

Still no luck....I tried resetting the ECU (disconnecting the IAC and letting it idle - i'd let the screw out a bit instead of it just being fully tightened), turned on the car and the idle was fluctuating really quickly between 1100-1200rpm (this is with the IAC disconnected and the idle screw loosened). Then loosened the coolant bleeding screw - only a few bubbles came out then it was fairly smooth flowing. Now i've tightened the coolant screw and connected the IAC and it's still fluctuating continuously between 1000-1500rpm...

Oh I also sprayed some carby cleaner into the IAC filter but i don't think that did much at all, the filter looked fairly clean.

I'm fairly certain there isn't anything wrong with the IAC because the idle does change when its connected to disconnected and vice versa.

I tightened the idle screw all the way back in and that brings the idle back down to about 1000rpm but i don't consider this a proper fix, it should be much lower with the screw tightened all the way in :S

Any other ideas guys? cos this is REALLY giving me the ****s.