4AGE Blacktop 20V IACV
Posted: Mon Aug 26, 2019 3:22 pm
Hello, are there any USDM IACV's that are compatible with the 20V IACV? I bought a used one on ebay after experiencing a high idle with my old one and now I have a rough idle.
GNG45 wrote:Hello, are there any USDM IACV's that are compatible with the 20V IACV?
I bought a used one on ebay after experiencing a high idle with my old one
and now I have a rough idle.
jondee86 wrote:GNG45 wrote:Hello, are there any USDM IACV's that are compatible with the 20V IACV?
I bought a used one on ebay after experiencing a high idle with my old one
and now I have a rough idle.
Have you tried cleaning the valve (blasting carb cleaner down the tubes until
no more black stuff comes out)??
Cheers... jondee86
jondee86 wrote:The ISCV modulates (changes position smoothly) the amount of idle air entering
the engine by opening and closing as instructed by the ECU. If you like, it will
change the engine speed much as if you were keeping the engine running by
gently opening and closing the throttle a fraction.
It is unlikely that the ISCV would actually CAUSE a rough idle. But if the engine
rpm was fluctuating because af misfiring, the ISCV might be trying to catch a
falling rpm and overcompensating. My engine sometimes gets a bit of a rich/lean
lope, and the ISCV can magnify that into a huge "supercharger lope" Sounds like
I have a cammed 427 with a 671 on top
So if the replacement ISCV does not cure the roughness, you will need to look at
things like the TPS setting, plugs and ignition timing.
Cheers... jondee86
jondee86 wrote:Make sure that the hose for the MAP sensor is not split or leaking. Check that the
water temperature sensor for the ECU is not broken ior unplugged. Black plugs usually
mean that the engine is running rich. Once you have checked the above put in a new
set of plugs, then check the TPS setting and ignition timing.
Cheers... jondee86
jondee86 wrote:Cycling on the fuel cut... engine speed above around 1700 rpm and closed throttle.
Back the engine speed down to 1500 - 1600 rpm and it will stop doing that
Cheers... jondee86
jondee86 wrote:First up you don't want your throttle cable to be tight. The throttle arm must return
and rest on the throttle stop to make sure that the throttle butterfly is fully closed
when you are off the gas, The cable itself should have just a little bit of slack so it
cannot hold the throttle arm off the throttle stop.
The ECU is set up to cut fuel delivery to the engine when the car is on the overrun
with a closed throttle. There are preset limits to control when the fuel is cut off and
basically the engine speed needs to be above 1700 rpm and the throttle closed before
fuel cut happens. Once the fuel is cut, the engine speed needs to drop below 1400 rpm
or therfabouts before the fuel turns back on (or you open the throttle).
Now we get to the trick part that I am not totally sure about. With quad throttles
the throttle butterflys only have to be cracked open by a tiny amount to push the idle
speed up. Most aftermarket ECU's call the throttles closed when they are less than
1% open, which means you can actually have a 2000 rpm idle even though the ECU
considers the throttles closed and initiates fuel cut. A vacuum leak will cause the
same issue by raising the idle with closed throttles.
So the idle speed goes high... fuel cut occurs.... idle speed drops... fuel is restored...
idle speed goes up... fuel cut occurs.... and there you have it
Cheers... jondee86
jondee86 wrote:Remove the filter from the fresh air side of the ISCV and block the end of the
tube with your thumb. You should be able to regulate the idle speed by varying
the amount of "blocking" you are applying with your thumb. Tptally blocked the
engine should either stall or drop to a very low idle like 400-500rpm. If it does
not behave like this then your engine is getting idle air from someplace else.
Either the throttles are not fully closed or there is a vacuum leak.
Cheers... jondee86