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Causes for hunting at idle...?

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Took the s15 out for a drive this morning and after a couple of minutes came to a stop, and the revs were hunting up up and down between 1k and 2k.

Turned the engine off and back on then it was fine. What could cause this and anyone have any recommendations / ideas?

Idle control valve? Throttle position sensor? Lambda?

Cheers

Parky
 

S15_SAM

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Could be a few of those tbh, or even Afm or fuel pump. Best take it to engine tuner in Devon as he knows S15's well.
 
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Cheers fellas. It only seems to be after a cold start, idling is fine once it's up to normal running temperature, sits at about 1000rpm more or less.

Whereabouts is the idle control valve on the DET? Attached to the inlet plenum?
 
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yep, on engine side of intake plenum, near the back, unless its worn off the sticker on it will say AAC VALVE, careful with the gasket as it rips easy, i ordered 5 of them from RHD about a $3 each should last me years and years as i clean this valve every year
 
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Cheers, gonna have a look at getting it sorted this afternoon
 
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Right I had the Idle control valve off, was pretty mucky inside so cleaned it up. I almost snapped an alan key trying to get the TB off so left it in place, and cleaned the inside the best I could. Had a look at the AFM, cleaned that, and it looks to be in good shape. It did seem a little better although not by much.

I'm confused as to why it hunts and idles high at a cold start, but is steady once warm.

This video is from after refitting it all. (I revved it at 0.23). After a few attempts of shutting down and restarting it did the same each time.


Any ideas? Would rather try and sort it myself to save cash but I will take it to the fella in Devon as suggested by Sam if all else fails.
 
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NEXT time or if anyone else in the future asks this

1) unplug the two sockets,
2) undo the 3 bolts holing it in place,

3) remove the AAC housing, which will have the two sensors on it.
4) unscrew the large one ( has AAC written on it Brown plug) keep close in mind how the pins and screws go together so as to put them back in the correct way when removing the valves.
5) unscrew the skinny one (hexagonal shape purple plug on it) as above with the bits
6) get something like throttle body cleaner and spray the hell out of the housing and all its galleries (really good degreaser in a spray can like CRC throttle body cleaner)
7) spray down into the sensors parts where the air pushes the valves up and down to get all bits of crap out of them, and clean the spring and pistons looking bits. MOST IMPORTANT BITS
8) put back together..... if you bugger the gasket, get another one...
 
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has your cold idle screw come loose? or has it beet tinkered with?
 
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Thanks for the replies Spoonman. I didn't take the AAC Valve apart so will do that later this week.

I don't know to be honest, whereabouts is the cold idle screw? and how should it be set?

Cheers again.
 
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Mine does this assumed it was just cold start automatic chalk
 
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look at you throttle body, there are two screws the top one is hot idle , near the bottom is the cold one, you can see hose connections going from the right to the left of the TB these are where coolent goes through and how you get cold and hot idle,

look at the FSM its downloadable from the usefull section on this site
 
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Gave the idle control vavle a good clean as per Spoonman's guide earlier and it seems to have done a lot of good. The throttle cable also seemed a little tight so loosened that off a bit. Seems as it should be now, will keep my eye on it though. Cheers
 

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Cold idle is normally 1500-1800. I adjusted my cold idle screw out completely so it didn't kick in because it would rev to high on start up.

Mine still idles around 14-1500
 
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Thanks Sam. I noticed while I was refitting the idle control valve that the throttle pulley stopper pin wasn't sitting in the same place as it had been on the part you were pointing to in your photos (I could see a mark where it had previously been hitting) so I adjusted that back with the 8mm nut / threaded pin to it's original position and it sits at roughly the same as yours, around 1500.

Think this may be problem solved, will keep tabs on it though.

Cheers for the help y'all.
 

S15_SAM

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Even with my cold idle valve off it still idles around 1400 sometimes. Think it's due to the cold climate over here. It's raining today.....same as most days
 
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