Fast idle when coming to a stop

roders · Post by **roders** » Wed Nov 09, 2016 7:24 pm

I have an odd situation occurring on my G3 89 2.0i 16v 4ws when the car comes to a stop at a junction etc when warm.
The revs sit at 2000rpm for 5-6 seconds, then fall to tickover at about 8-900rpm, and idles steady.
I have replaced the EACV with a new one, and the car idles perfectly when cold so fast idle valve seems to be working ok.
Have had the mixture checked at my local Honda dealer by mechanic who worked on this car when it was new, and this is fine. He is also at a loss as to why the car behaves like this!
If I unplug the EACV the car drives ok, and problem goes away, but won't idle properly when cold as if fast Idle valve is faulty.
Car also drives perfectly with no sign of a problem, until you come to a stop.
Has anybody come across this problem before, or got any ideas I could try?
Help,this is driving me mad!!!!

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Wed Nov 09, 2016 7:52 pm

It's not just the throttle cable sticking, is it?

roders · Post by **roders** » Wed Nov 09, 2016 10:23 pm

No it has slack in it. Have also sprayed all vacuum hoses with contact cleaner with no change. I am completely baffled.

Post by **NafemanNathan** » Wed Nov 09, 2016 11:06 pm

Possibly your FITV (Fast Idle Thermal Valve) bud.

I had pretty much the same issue. Replaced the IACV and various thermal sensors with no joy, but then have a read here...

http://www.ludegeneration.co.uk/post105040.html#p105040

roders · Post by **roders** » Thu Nov 10, 2016 5:41 pm

I had discounted FITV as the car runs, and idles fine, hot and cold. The idle may be a little high if anything around 900rpm when warmed up. Maybe I have been mistaken.
I did wonder if there was extra air getting in the system, and then the ECU detects this and gives it some more fuel to compensate, but it only happens when then car is moving. I have sprayed all the vac lines, but that made no difference.
Thanks for the link NafemanNathen, it looks as though the EVAC is also detecting electrical load on the car as well. It's a lot more complicated than just being open or shut as I thought with my bench tests of it with a battery!

Post by **NafemanNathan** » Fri Nov 11, 2016 8:10 am

Something is obviously allowing more air into the intake plenum if the revs are lifting.

You've replaced the IACV and assume by mixture you mean you've replaced the coolant and bled it through?

Have you considered the thermo sensor?

Are you able to get the issue to occur when the car is stationary (possible to work on)? If so you can easily rule out the FITV.

roders · Post by **roders** » Fri Nov 11, 2016 8:52 am

By mixture, I mean fuel/air adjustment, this is spot on.
The problem only occurs when coming to a stop after moving, so is impossible to replicate when stationary in the garage.
When stationary the idle is ok.

I will try and see if the FITV is still passing air when the engine is up to temp to see is this is the cause.
Thanks for the thermo sensor idea, I will check that as well.