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Discussion Starter · #1 ·
So I bought a 97 WRX with a Check Engine light. Code 24: Air Idle Control Valve or circuit fault apparently.

The car has a fluctuating Idle at just under 1500rpm and fuel cut enabled obviously from the fault.
Sometimes the Idle will smooth out for short periods of time and I think it's when the radiator fans kick on and off but I'm not 100 sure.

I cleaned and even replaced the valve but it didn't change the running condition or remove the light at all, absolutely nothing.

I unplugged the valve while the car was idling and that also didn't change the engine RPM or anything. It's like the valve isn't working at all.

I smoke tested the intake and can't find a vacuum leak and the valve is getting 12 Volts on the middle pin and both other wires trace back to the ECU so I'm kind of stumped.

When I unplug the TPS and start the car the idle goes very high, so I'm assuming that is working correctly.

If anyone has any ideas on why the valve doesn't seem to activate that would be amazing.

I've seen a lot of posts about the Code 24 but all the ones I've seen are intermittent. Mine is constantly on form when I put the key in the ignition.

Thank you again for any help provided. I've had the car for over a year and can't figure it out馃ゲ
 

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Did you unplug the battery to reset the ECU after cleaning and/or replacing the part? The car needs to learn that something was replaced or it'll likely just produce the same map. Also if you didn't replace the IACV gasket it's good to use a new one since they are flimsy and can break easily.
 

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Discussion Starter · #3 ·
Did you unplug the battery to reset the ECU after cleaning and/or replacing the part? The car needs to learn that something was replaced or it'll likely just produce the same map. Also if you didn't replace the IACV gasket it's good to use a new one since they are flimsy and can break easily.
Thank you for replying to my post.

I did indeed remove the battery. A actually removed it and left it out overnight.
I did read that you should replace the gasket. I installed a brand new OEM Subaru one when I cleaned the valve.

Its very odd that the RPM doesn't change when I unplug it though. I'm wondering maybe another sensor might be stopping it from activating 馃し.
 

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the IACV is a stepper motor so just unplugging it temporarily wont do much cause it's exactly where the ecm last commanded it to be and wont be an issue. unplug it before a cold start and see what happens, you likely just need a new one though. the smoke around the turbo could be.... an exhaust leak, coolant leak, or an oil leak... hard to say.
 

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Discussion Starter · #6 ·
the IACV is a stepper motor so just unplugging it temporarily wont do much cause it's exactly where the ecm last commanded it to be and wont be an issue. unplug it before a cold start and see what happens, you likely just need a new one though. the smoke around the turbo could be.... an exhaust leak, coolant leak, or an oil leak... hard to say.
Yeah the smoke doesn't seem retated but you never know. I have replaced the valve with 2 others and all three do the same thing馃ゲ
 

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I didn't look too hard... googled "1997 wrx fsm". the 93-96 fsm doesn't appear to have the page for what to do, that section of the scanned manual seems to jump around. and the 97-98 fsm appears to be informational only and not repair.
 

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Discussion Starter · #10 ·
I'd be looking in to the circuit then. find a factory repair manual and follow diagnostic steps for the code.
I have a full service manual. I did the steps in the Code 24 Diagnostic Chart

I get the correct input signal for the ECM. It then tells me to check poor contact in ECM connectors but they all have continuity.

The Valve Solenoid has 9.5ohms of resistance on pin 1 to 2 and 3 to 2 like it should and pin 2 has 12 ignition power.

GC8 Code 24 Diagnostics Chart
 

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i'd be looking at the throttle body next. it may be gummed up and stuck open and the ecm is thinking that's poor IACV performance.
 

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Discussion Starter · #12 ·
i'd be looking at the throttle body next. it may be gummed up and stuck open and the ecm is thinking that's poor IACV performance.
Thank you for the recommendation. I cleaned the throttle body. It wasn't actually that dirty. Unfortunately it didn't really do anything.
It has to be a wiring problem or something but I get all the right voltages out of the valve 馃槶
 

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Check all the female connectors to see if maybe one of them is spread too wide to make good contact with the male parts. easy for a multimeter probe to touch but not the tiny pins in the connector.
 

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Discussion Starter · #14 ·
Check all the female connectors to see if maybe one of them is spread too wide to make good contact with the male parts. easy for a multimeter probe to touch but not the tiny pins in the connector.
I'm getting full continuity from the valve to the ECU. But I'll definitely check them. I'm going to have another look at the throttle. I'm wondering if maybe the cable is not adjusted correctly. It might be stuck open
 

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Did some googling as I'm not really familiar with OBD1 systems other than I know that they're dumb and send you on wild goose chases. Someone explained that Code 24 sets when the ECM commands a change to fueling, and doesn't get what it expected. There could be an issue with any thing related to fuel, intake or exhaust. MAF, IACV, TPS, O2's, maybe even injector(s), I bet I'm missing things too... one guy said he unplugged his battery for 30 minutes and it never came back.

So, good luck buddy! You have an intake leak, exhaust leak, or a sensor that's on the fritz.
 

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Discussion Starter · #16 ·
Did some googling as I'm not really familiar with OBD1 systems other than I know that they're dumb and send you on wild goose chases. Someone explained that Code 24 sets when the ECM commands a change to fueling, and doesn't get what it expected. There could be an issue with any thing related to fuel, intake or exhaust. MAF, IACV, TPS, O2's, maybe even injector(s), I bet I'm missing things too... one guy said he unplugged his battery for 30 minutes and it never came back.

So, good luck buddy! You have an intake leak, exhaust leak, or a sensor that's on the fritz.
So I got my brother to hook an ocsilascope to I pin 1 and 2 of the IAC valve. This signal looks strange to me but maybe it's fine. I don't know what I'm looking at.

 
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