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may have this in the wrong spot-

I have code 24 coming up - car idles at 500 rpm or so and after a run I get the CE light saying that the ISC is playing up.
so location and resistance/voltage values would be helpful. no other errors.
engine is a 1995 EJ20H (though I figure a EJ20G would be similar)

ta!

off another forum
a-c 15 ohms
a-b 9 ohms
b-c 9 ohms

http://www.rslibertyclub.org/forums/sho ... =ISC+error

Should be part of the throttle body. Its a servo that opens to increase idle speed when the engine is cold, or when you switch the Aircon on.

This is the ISC from a 93 WRX
http://www.linkecu.com/support/dlandswu ... lation/A01

This might be worth a read too
http://forums.nasioc.com/forums/showthread.php?t=781242

Does the engine idle higher when its cold? when the ac is switched on?

On the 20g's the IAC/ISC is on the back #4 intake runner, has a 3 pin plug and A, B & C labels. On the 22m's its on the rhs of the throttle body, on the pelum chamber.

The unit is most likely jammed/sticky, take it off and see if it moves freely and smoothly.

The coils should measure 9 ohms between the common (centre I think) pin and either control pin.

The plug should have supply voltage at the common, the other two pins pwm grounded via the ecu.

For the 20g:
ON (engine off) pin1 8-9v (on 26 pin plug)
pin2 6-7v

Engine ON pin1 9-10v
pin2 6-7v

Also have noticed on the 20g/22m the black wire on the IAC is actually white at the ecu, and the white wire on the IAC is black at the ecu.
They change at the engine harness plugs. It is meant to be like this, don't swap them over!

Good Luck.

I found it. mine has a damaged plug but the connections are fine. resistance values I didn't check - votlage I did - supply on middle pin - 10v or so on one . 0v on the other engine running. so it looks like the issue lies elsewhere. I'll check the TPS later. been under this thing for 3 hrs now and had enough

ISC faults can occur simply because it is sticking. Undo the screws that hold the motor on top and check that the valve swings freely.
There is not much else that can go wrong(other than failure of the motor wiindings) if there is 12v supply and the open and close wires have continuity and aren't grounding.
My bets on sticking valve. If the ecu is driving the valve open and the idle speed doesn't respond it will set a code. This is a common fault with manual cars that don't have a neutral switch too.

ok - took it loose - valve swings freely. windings are fine. can I hit it wth WD 40 to loosen it a bit more. when I do a AC Request it idles up so the valve must work. I cannot tell if it cycles when I do the actuator test ( green plugs.) though.