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Car is Impreza 1997 Rx 2 litre

So, over the last say 6 months, I've had the engine light coming on when decelerating from anywhere over 60kmph. I've ran diagnostics on the computer and found out the error occurring was "24. Idle Control System Malfunction" I've taken my car into Subaru Geelong for a check up. They Seemed to think the issue was a build up of carbon in the throttle body. Gave me some throttle body cleaner and sent me on my way. So I've cleaned the throttle body out... Still the Engine light. Next step was replacing the IAC Valve. I acquired one off ebay from the US. Same Product number and details as the current one in the car. Replaced that, Still the engine light.... So, I've taken it back to Auto Electricians workshop and did the diagnostics again.. Same Error, "24. Idle Control System Malfunction"... He suggests it might be the computer.. So, we look into buying a refurbished computer.. $800, scrap that; we "Hired" one for use and still the same error.. Since then I've bought a reconditioned AIC Valve for $700. 100% working order. New fittings, the works... Yet still the same Error. Eventually after a period of time.. the Engine light stays on longer and longer... won't turn off.. Then will not turn off and idle very rough and feel like its about to stall.. Quick fix of turning the car off for 2 seconds, back on... running like a dream.. Rev's are fine.. Everything else seems to be fine.. Just knowing there is a problem is the issue.. If anyone could possibly suggest any other options other then buying a refurbished engine would be muchly appreciated... Subaru Geelong is stumped and wanted to sell me a new Computer and IAC... Which wouldn't of worked either way. Fast way to waste $2,000 on a car Valued at $5600... I plan on keeping the car till i'm off my P plates.. But would like this problem to be eradicated ASAP. Any Suggestions would be muchly appreciated!

Cheers, Ryan.

Hi and Welcome Ryan,

What parts did you replace on the IAC valve? was it the coil on top or the valve body below that?

Is there any non factory parts on the car like an aftermarket air filter, silicone hoses, etc... ?

Have you had a compression test lately? or service?

Cheers,
Paul

Did a service about 3 months ago. Replaced the valve body . No aftermarket air filters or hoses to my knowledge. When I did a service I also replaced the rear main seal and the two cranks half seal and a camshaft seal. Replaced the timing belt, clutch and fly wheel. No compression test to date.

The whole part '22650 aa034' was the part. The whole assembly, cheers

Could it be a wiring fault?

Check the Vehicle Speed sensors, if they are faulty it doesn't matter how many "good" IAC valves you swap, replace or diagnose the IACV will throw a fault. as ecu isn't getting the correct reading from the VSS so it gives the IACV a faulty reading which makes it look like it is malfunctioning.

TOONGA

Could be an idle switch/sensor issue or even a throttle problem.

I had an IACV fault code and revs that would constantly rise and fall. After replacing the IACV to find the fault was still there, I discovered that the throttle cable was too tight holding the throttle open and not allowing it to idle low enough.
The ECU only guessed the IACV was faulty

I'd grab a copy of the Work Shop Manual and check the input/outputs on the wiring to the IACV.

I'd also have a look at what Gannon is saying about the throttle cable

We checked all the potential issues that yous have recommended and nothing has given results unfortunately. Did a theory testing and the light will always come on decelerating from 100-80 at 2,400 rpm. Still stumped for idea's any other idea's would be great

Cheers
Ryan

Is the IACV code the only one coming up? As there could be an issue with the power supply from the Ignition Relay. These relays are prone to failure and there is a thread on here that shows how to convert it over.

So, Problem has been resolved. The Natural Switch in the gearbox for 1st,3rd,5th gear had been too worn and was giving a false reading causing the light to come on at deceleration. so, once that was replaced worked like a brand new car again. Also tested the relay after we replaced the iac valve. So, The answer was the Natural Switch in the Gear Box... $1,000 later. Apparently it hasn't happened before.

Excellent news and glad it's sorted

I am a little confused as the Neutral Switch is code 51 but there is also code 42 that relates to the Idle Switch, so I wonder if someone was reading your codes incorrect as 42 and 24 could be mixed up.