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Unusual idle then check engine light


RaKid

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Hi team,

 

Started car from cold this morning and got to the first set of traffic lights. Noticed car was idling at 1500rpm which is a little unusual for my car (it usually hits warm idle very quickly).

 

Drove about another 1km to my destination, stopped car for 10min (and turned off), started car and drove to next traffic light - rev meter fluctuating between 500 and 2000rpm and can't settle on a number.

 

Engine check light came on.

 

Drove 20km to destination (motorway) and 1km before destination the engine check light went off. When I reached my destination I let the car idle for 30secs. Revs at 500rpm the slowly climbed to 800rpm over 10 seconds.

 

Vehicle is 1997 WRX STI.

 

Is this my o2 sensor?

 

Thanks in advance for any help or advice.

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There are a few yeah, but basically you want to fish around under your steering column for a couple of pairs of plugs; one green set, and one black. Plug the black ones together, turn your ignition on, and count the flashes on your dash CEL. Long flashes are 10s, short flashed are ones, eg: two long flashes and three short is 23. Once you have the code, you'll be able to ask here or look it up via uncle google.

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35 minutes ago, RaKid said:

Hmmmm

 

Unusual idle sometimes can indicate a dirty or defective AFM - first thing i would do is get a can of AFM cleaner and clean your AFM - I ended up solving this issue on a Legacy I had by replacing the AFM

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Just now, V7STI1992 said:

 

Unusual idle sometimes can indicate a dirty or defective AFM - first thing i would do is get a can of AFM cleaner and clean your AFM - I ended up solving this issue on a Legacy I had by replacing the AFM

 

OK this sounds good. I'm pretty keen to see if I can get a CEL code before I do anything but it's worth trying this too.

 

I'm just trying to avoid taking it into a shop.

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  • 2 weeks later...
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On 11/7/2016 at 9:12 AM, GC8E2DD said:

There are a few yeah, but basically you want to fish around under your steering column for a couple of pairs of plugs; one green set, and one black. Plug the black ones together, turn your ignition on, and count the flashes on your dash CEL. Long flashes are 10s, short flashed are ones, eg: two long flashes and three short is 23. Once you have the code, you'll be able to ask here or look it up via uncle google.

 

2 long and 4 short is what I'm getting

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24 Air control valve Air control valve inoperative (Abnormal signal produced in monitor circuit) Prevents abnormal engine speed using "fuel cut" in relation to engine speed, vehicle speed, and throttle sensor position

Idle speed control solenoid valve

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I think there are 2 try taking them off and crc the bearing under them and twisting with hand to loosen it up

 

one does idle so when cold it runs higher revs then heats up and revs go down, ive had this one seize in the bearing from using just water instead of coolant and letting the engine sit for a year

 

check wires and plugs to these sensors for debris/bad contacts and check in areas you hve recently work on in engine bay incase youve accidentally unplugged somehing

 

cheap fix to replace if that fails though

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11 hours ago, THUNDA said:

I think there are 2 try taking them off and crc the bearing under them and twisting with hand to loosen it up

 

one does idle so when cold it runs higher revs then heats up and revs go down, ive had this one seize in the bearing from using just water instead of coolant and letting the engine sit for a year

 

check wires and plugs to these sensors for debris/bad contacts and check in areas you hve recently work on in engine bay incase youve accidentally unplugged somehing

 

cheap fix to replace if that fails though

 

Hey mate appreciate that a lot. I did read somewhere that it was air related so I appreciate your post. Will play with the ICV and see how I get on

 

10 hours ago, slystiguy said:

check for vacuum leaks

 

So far all the vacuum looks really good!

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It's only fair everyone gets an update.

 

Last night I loosened the adjusting screws on top of the IAC to adjust the idle RPM a little lower, took vehicle for a drive and IAC is fine when car is cold. The second car reaches operation temp there are issues. Car will stall as the revs drop because it can't seem to 'activate' (for lack of a better term) the IAC

 

Removed TMIC. Removed IAC. Black as anything. Cleaned out.

 

To do: Fit back cleaned IAC, take car for test drive and check for previous symptoms. If gone, clear CEL, if not, fit second hand one I just bought.

 

Any thoughts?

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These type of problems are difficult to diagnose online but it certainly sounds like IACV or AFM related. You haven't got any intake leaks after the AFM right? Even a cracked hose or leaking bov? There's a tiny hose on the bottom of the stock air box resonator which is often overlooked make sure it's plugged in or capped off. 

 

The other thing you could look at was coolant temp sensor. But I'd try resolve the IACV code before going too much further. Clean the S*** out of it and check the wiring in the plug hasn't pulled away or that the wiring to the sensor isn't damaged. 

 

If you have a vacuum leak it will generally give symptoms like start run fine for few minutes or until you give it throttle, then it will try to stall/fluctuating revs as unmetered air is getting in and upsetting the ecu

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Sorry - I was meant to update everyone. Fixed!

 

When I put the IAC valve back on I've removed the top piece and had a fiddle and put it back on reverse by mistake. So I still had the same issue (not idling correctly) but it was slightly different. Presumably I was sending a negative voltage back to the ECU or something quirky like that.

 

Removed the top piece and flipped it the correct way around and it's working perfectly.

 

So all I really did to fix this issue was clean the IAC valve with wheel cleaner in Mum's sink and put it back.

 

Thanks for everyone and anyone that had input.

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