Help me out, list what to check for the famous idle surge between 800-1200 RPM.

 

Likely culprits are the IACv (idle air control valve) and the FITv (fast idle thermo valve). In cases where the idle surges from 1000-2000 (1000 rpm lope) it is likely the IACv. In cases where your idle surges much less (800-1200, about a 500 rpm lope), this can sometimes be traced back to your FITv malfunctioning.

 

You could try a search, but 99% of the time its either iacv (clean/replace) or fitv (clean), that 1% of the time its low coolant or vacuum lines i believe.

 

When my IACV went it was about 1000-2200, So I would guess FITV or Vacuum leak, I found 100s of posts about it when I had a problem

 

Where is the FITV located?

 

talk about internet delay, i didnt see anyone when i posted. but also i believe the fitv controls idle during warm-up then iacv takes over, if that helps any.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by z6hatchboy &raquo;</TD></TR><TR><TD CLASS="quote">talk about internet delay, i didnt see anyone when i posted. but also i believe the fitv controls idle during warm-up then iacv takes over, if that helps any.</TD></TR></TABLE>

That is true.

The way the FITv works is that it is a valve that allows a controlled vaccum leak when you have a cold start, allowing a higher idle (as if you were pressing the gas and opening the throttle butterfly), without the actual butterfly having to be opened. Over time, this valve can wear out, and get stuck in the 'open' position, causing a small lope in idle, just as a vaccum leak might.

 

Thanks for the "how it works" info, really. And do you know the its stock position, as in how many turns from all the way in its set at? Im about to clean mine before i put my motor back in so i wont have to worry about later, and the 230k my t/b has on it,lol.

 

Ok so let me throw this into the problem, BRAND NEW from Honda IACV, all coolant hoses to the IACV and FITV are disconnected and capped off. Now what does it leave as a likely culprit?

Searching didn't stir up any results and as stated 99% of the time it is the IACV.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Pure Sol &raquo;</TD></TR><TR><TD CLASS="quote">Ok so let me throw this into the problem, BRAND NEW from Honda IACV, all coolant hoses to the IACV and FITV are disconnected and capped off. Now what does it leave as a likely culprit?

Searching didn't stir up any results and as stated 99% of the time it is the IACV.</TD></TR></TABLE>
If your IACv isnt having coolant run thru it, it wont function correctly, if thats what your getting at by saying its all "disconnected"

 

Correct me if i'm wrong but my understanding is the FITV relys on the coolant to function correctly but the IACV is controlled by the ECU.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Pure Sol &raquo;</TD></TR><TR><TD CLASS="quote">Correct me if i'm wrong but my understanding is the FITV relys on the coolant to function correctly but the IACV is controlled by the ECU.</TD></TR></TABLE>

Thats correct about the FITv, it relys on coolant temperature for operation. The IACv also relies on coolant to opperate as well. Try starting a motor that has no coolant (just to get it running) with a fully functional IACv. It wont hold an idle and will die out. The IACv relies on coolant flow to function properly. This is why airbubbles in the coolant system that flow thru the IACv can cause funky idle issues.

 

Even though my IACV has been "disconnected" for some time, in the interest to try and fix this issue I'll hook that back up to coolant and see if the situation corrects itself. I appreciate the help and will update when I get it back to stock.

 

if you try all that other ****, and it still don't help, check to see if you have a vac. leak, with the motor running, take off the intake tube, and cover the TB with your hand, (while motor still running) if motor turns off, you don't have a vac. leak, if it stays running, you have a vac. leak, you will be able to find the leak by the sound, have fun

 

Thats an interesting way to test for a vac. leak. Never heard that one before, I'm pretty sure I don't have a leak though. I can sit still at a stop and let it surge, however if I put a slight load on the engine and drop the RPM's down and release the load it kills the surge for a brief time. If it were a leak the RPM's would not stop surging. Thanks for the insight though.

 

Back to the top, still have a hunting idle (800-1200). With the IACV there was no change. Any more ideas?


Modified by Pure Sol at 4:06 PM 12/31/2007

 

bump