Intermittent Idling problems

I've had a small problem with idle since the PowerFC was fitted - I am just posting this here to get some ideas, until I can see Ryan again because it might not even be to do with the PFC itself, may be a coincidence but it did happen right afterwards.

What happens is that the engine will randomly rev to over 2,000 rpm when I am at idle, if and only if the air con or lights are on, i.e. there's extra load on the engine. However, if I am already at a good idle (800 rpm) and I switch the lights on, the revs increase to about 830 as normal. It's only when I blip the throttle that the revs go high.

Sometimes the revs will drop back down again after a few seconds, then back up of it's own accord.

Ryan's suggested a sticky idle control valve. Would the explain the revs sticking high AND randomly going low and high again?

The standard toyota Ecu has a higher *idle feedback below rpm* set which means that the closed loop idle system corrects the idle if say it rises up to ~ 2000rpm.

With the powerfc it has a much lower rpm feedback level set and only corrects up to ~ 1500rpm so if you idle sticks it will not correct it (can't change this with powerfc software )

The reason i say it's the idle control valve sticking is because the car idles correctly if say the A/C or lights are turned on at the normal idle speed as this i tested at the end of the mapping session and you comfirmed above. Though when the ISCV sticks say coming down the rpm from say blipping the throttle the ecu will not try to fix if it is over the set feedback rpm area.

B'have had this problem also. Quick clean of the ISCV and sorted

Ryan

Cheers mate, the feedback value explanation you gave is the missing link in my mind.

I will locate this valve and give it a clean

In my experience the PFC has less than brilliant idle speed control on some engines. I have never got a very good idle stability on my Skyline or RX-7 engines with them. Acceptable, but not good.

In my experience the PFC has less than brilliant idle speed control on some engines. I have never got a very good idle stability on my Skyline or RX-7 engines with them. Acceptable, but not good.

I don't mind if it's a little unstable around 800-1000 hunting around a bit, it's just when it goes to 2000!

I've had a search of the forums and can't find any information on how to locate / clean the ISCV - any pointers?

Guys is this the ISCV?

http://www.mkiv.com/techarticles/parts/iac/index.html

It is on a UK / US one.

It is on a UK / US one.

OK

Is it the same principle for a j-spec? I guess I'm looking on the throttle body somewhere. Is it easy enough to take off and clean?

It is on a UK / US one.

OK

Is it the same principle for a j-spec? I guess I'm looking on the throttle body somewhere. Is it easy enough to take off and clean?

I tend to fit new ones, they rarely seem to work the same when you fiddle with them, having said that Supra ones seem very reliable.

I tend to fit new ones, they rarely seem to work the same when you fiddle with them, having said that Supra ones seem very reliable.

I will probably have a go at cleaning mine, as it may isolate the fault, and I haven't lost anything if I then decide to get a new one.

Any pointers appreciated

I had exactly the same issue with my car (also PFC) and after cleaning the IACV it seemed to solve it. Unfortunatly the new owner had the same problem a few months later and solved it again with replacing the terminally b*ggered IACV)

Homer is that the same thing as the ISCV? Acronym overload!

The Idle Air Control Valve is the one at the back of the intake manifold (The one prone to 'sticking' when gunked up)

It's often referred to as the ISCV (Idle Speed Control Valve) hence some of the confusion. On the Toyota manual they call it the IACV hence why most here call it that. They're the same thing, just need to learn those acronym's

Excellent. I have found loads more information about the sticking IACV issue so feel confident looking at this now.

This may be a silly question but why does the IACV need a water feed?

On the Toyota manual they call it the IACV hence why most here call it that. They're the same thing, just need to learn those acronym's

Are you sure Because the IACV is the Intake Air Control Valve, part of the sequential system. The idle controller is referred to as the ICV, Idle Control Valve, presumable to (how we laughed) avoid confusion over the acronyms

-Ian

Are you sure Because the IACV is the Intake Air Control Valve, part of the sequential system. The idle controller is referred to as the ICV, Idle Control Valve, presumable to (how we laughed) avoid confusion over the acronyms

Arrrghhh! Head Wall

Is it the "thing" at the back of the intake manifold that I need to clean?

Yes

Yes

Thanks

After much swearing I had the ICV valve off this evening, it didn't actually look very mucky at all (no EGR ), but I cleaned out the body with Gunk degreaser, rinsed and dried it, and the check valve and re-fit it all.

Initially I thought I'd fixed it but the problem is still apparent when I turn the A/C on. The revs jump to about 2100, and hunt around about 1800-2100 until I turn the A/C off again.

The lights don't seem to affect it any more, so perhaps cleaning the IAV did "something" but not fixed it completely

Could this problem be related to the TTC mode, at all? As that was done at the same time as the PFC install.

I will have alook mate when i see you soon and will get it to relearn the idle setup again.

Not like you need the a/c this time of year anyway

Ryan

cheers I felt like I was doing something useful anyway!

I wish I didnt need air con at the moment but I have a bit of a moisture issue right now. Window seals I think - it never ends!

Right, this has been bugging me so I've done some more troubleshooting today. It's definately not the ICV as when I get the high idle my TPS reads higher as well, as if the throttle is stuck on a little.

With this in mind I went to have a look, and sure enough, if I tap the throttle control arm (on the other side of the throttle body to the cable) where it hits the "dash pot" (I identified this from the EPC), the idle returns to normal.

So it looks like the dash pot thing is holding my throttle too high sometimes. It's not connected to anything so I think it's just there to dampen the throttle. Do I need a new one, do they go bad like this?

It probably just needs re adjusting, i posted a pic from the manual a couple of days ago, which will help.

They do have a little foam filter inside them, the cap pulls off and inside is said filter. I don't know if that makes a difference or not though.