SR IACV (AAC) (Not your average problem)

SON240sx Automotive
1

Okay, So since I got my SR I have never been able to get it to idle right. I have finally narrowed down the problem, and boy does it have me stumped. So hopefully some of the more experienced SR owners on here can give me some helpful information. So here goes.

The problem is with my IACV (As if you couldn’t have figured that out from the topic) Anyways here is a list of what I’ve tried so far.

I took the IACV off over the winter cleaned/rebuilt it and resealed it onto the intake collector. I start the car let the ECU come out of cold start (the RPM’s drop from 1300 to about 850) Blip the throttle and when the revs come down the motor stumbles and almost stalls. So the problem with my IACV wasn’t fixed with a clean/rebuild. I also re-wired / checked my harness over the winter so I know its fine but just for my own sanity I unplug the IACV and do a continuity test on the signal wire to the ECU (sky blue) it checks out fine. Then I proceed to check the +12 wire (black w/yellow strip) also checks out fine. So the wiring is good. Next I decide to see if the AAC solenoid is still working. I hook up +12 to the AAC and ground out the other side to the grounds on the intake manifold. The idle goes up on the motor so I know the valve just opened and its working.

(I know it’s getting long bare with me!)

Okay my next though is maybe the +12 for the AAC is bad even though it’s giving me a good reading. So I hook up the AAC again this time using the +12 from the harness (Black w / yellow strip) again idle goes up so it’s working. Next I decide to hook up a new wire from the ECU to the AAC for the ECU Signal (sky blue in the harness) I blip the throttle a couple times. Engine still stumbles WTF. I hook up my meter to the harness connector blip the throttle again, nothing no voltage spike or anything. Now I KNOW the +12 is good so it must be the ECU signal wire which should be grounding out in pulses to open and close the AAC to control the idle. Alas its not.

So now I’m stumped! Heres my conclusions from my tests

The Valve works because when I apply voltage, the AAC opens the valve.

The harness is good I did a continuity test and also tried hooking up new wires / +12 sources and it didn’t help at all

My next thought is well it must be the ECU. It’s a Blacktop SR with an E5 ECU. The harness was originally for a J4 but I repined it for an E5. So maybe I got the IACV pin wrong. EVERY S13 SR Source I can find says it should be in pin #113. Which it is. So its pinned right. I also found a couple places that said #115 was AAC so I did a ground test on pin #115 to see if it was pulsing a ground signal, its not. So I hooked the IACV up to pin #115 just for a lack of other options, as I though it didn’t work.

SO

Either my pin # no the ECU is wrong (if someone with an E5 ECU could see where there sky blue wire is going and let me know that would be awesome!)

Or for some reason my ECU isn’t sending out an IACV signal. Now I’m not sure if there is something that needs to trigger the ecu to send an IACV signal other then the RPM’s being below 1000 or what.

Any and all help on this is GREATLY appreciated! Heel toe blipping at every stop is getting annoying just to make sure she doesn’t stall on me… but on the bright side I am not the master of the bump start.

2

are you recirculating or venting to atmosphere your BOV?

if you’re venting then your spring isn’t stiff enough and you’re got a leak.

if you’re using the stock bov then you’re definitely leaking.

and I’m not sure about the nissan idle controllers, but I know the dsm ones have a wax element (much like a thermostat) and when they go back there is no way to fix it.

edit: the car should be able to idle fine with it unplugged.

so if you have it unplugged and still idle like crap… look somewhere else… like your BOV. and you mentioned that it dies after a blip or letting off the throttle… sounds like a bov.

3

Its not the BOV… and the car won’t idle properly without an IACV… whats what they do!

4

actually, they will, and do.

how do you think you set the idle?

5

I wasnt aware you were able to “rebuild” the IACV… you either had to just clean it or get another one and then mix and match parts to build a new one or what not (never heard of nissan actually offering a rebuild kit or anything)

I’ve also read of people cleaning them… getting ones from other engines and mix and matching parts and they still dont work… but once they actually go buy a new one, the problem is solved!

Whether this would be your case your not, I could not really say.

IACV can be a pain in the ass sometimes and on many cars “more so honda”

6

i would say, stiffen up the BOV and if you have an SAFC use that to help.
and buy a new iacv.

7

you shouldnt use a safc as a temproary fix for another problem.

8

Stick you doodle in it and that will fix the problem

9

The problem is DEFINATLY not with my BOV. I have tried blocking off ALL vacuum lines other then the FPR line as well as plating off the BOV to ensure there were no leaks. It still stumbles. Its defiantly an IACV wiring / ECU issue. The actual valve works fine… but its just not getting signal for what ever reason… which is what I’m tiring to figure out.

That only works on your G/F not car parts… thanks for the suggestion though. :slight_smile:

10

Hahaha nice nice,
dude if you wanna test your ECU I can lend you mine, I will not need it until next week when I get my cold pipe.

11

Needs to be an E5… you have a 62 for your redtop no?

12

Ya , ops. I forgot you had a blacktop MR fancy pancy

I am sure I have a 62 for my red top

13

heh, I’m telling you right now, the car will idle fine without the idle controller

uhh… dude… are you missing the BISS? that can cause the car to idle like junk… or any sort of vacuum leak.

don’t make me have to come down there :frowning:

14

the idle air control valve only effects cold starts

its similar to a choke on a carbed car

i should know since mine is unplugged it just makes cold starts and warmup bad

and you can use a E5 and 62 between each other ive done it many times.

15

drive over to the barn tonight dustypoo and we can hoss in my ECU

16

doesnt matter as DTS and stated…

True… but the E5 & 62 both read the O2 signal differently “according to enthaply” he states that the only differences between the two ECU’s is how they read the 02 signal…

Meaning… a 62 ECU needs a skinny O2 and a E5 needs a fatty O2 (in order to have a proper reading) he says something about each of them working off a different ground and if its not grounded you dont get a signal ?

17

i know exactly what you’e going through and 99% of SR owners go through this. im not sure if there is a definite answer other than standalone but this has always helped me:

#1 try to listen to the IACV and see if it is clicking. with a screwdriver up to it you should be able to hear some clicking similar to an injector. the IACV does work at idle

#2 if your TPS is set wrong or your idle is not calibrated correctly the engine will always be out of idle mode and be confused as to what it is supposed to be doing, not realizing that its job at the moment is to hold a current idle, or upon engine deceleration to CATCH THE IDLE (i.e. the IACV should go to a very high duty rate and let a lot of air flow in and slowly bring the engine speed down to 850rpm)

So what would make the car think it is not supposed to be idling? well if your TPS is tuned incorrectly and it thinks it is at 3-4% open when it is fully closed for example. Or if your physical throttle plate IS open slightly at idle. This is very bad.

Here is what you do:

loosen the 8mm throttle plate adjuster stick a flat head screwdriver in there and fully loosen it until the throttle plate is totally closed and touching the throttle body. now turn the flat head screw to open the throttle plate ever so slightly, just so the plate isn’t slapping the throttle body every time it closes. basically a quarter turn of the screw from the time it touches the stopper should do it. tighten the 8mm nut.

next check your tps voltage. i cant remember hte pin out you seem like you know what you’re doing though so make sure its getting its 12v and ground and test the signal wire. it should be exactly 0.5v iirc. again check the fsm tuning procedure for this. make sure it is at 0.5v if it isn’t loosen the two 8mm bolts and turn it until it gives you .5v

next turn the car off and set your idle. there is some crazy procedure for doing this in the fsm but it has to do with letting the car totally warm up turning it off unplugging the tps turning it on, holding it at 3000rpm, revving it a bunch of times letting it come down to idle, adjusting idle (iacv screw), hold at 3000rpm, rev it a bunch more times and check the idle. then repeat until the idle is good, turn the car off plug in the tps and then start it up again. like i said, check the fsm for the exact tuning procedure because im likely forgetting something there.

if all of that shit checks out and you know your iacv is working (which it seems to be), and you still have the problem then it has to be due to a vaccum leak / loose or shitty bov or something like that

18

Sasha

I tried #1 its not clicking at idle which is why I started diag. the wiring. I didn’t consider the TPS being slightly above .5v at idle as a cause for the IACV not to kick in but its a good point. If the TPS says its not at idle why would it engage the IACV. I tried the whole FSM set the idle thing last summer and I remeber thinking this is nuts… but I haven’t tried it again since I cleaned/rebuilt the IACV so I think its worth another shot.

Thanks for all the great info.

Mark! HELP! I can’t find the BOV fuse! Where is it? :lol:

19

BOV fuse, hah!

Mark is probably looking for it on his non-turbo car right now.

I’m in shock, you got an educated reply on SON!

I love you right now Sasha.

20

warm the car up to operating temp.
turn it off
unplugg the TPS AND IACV so that it’s not making adjustments while you’re adjusting the BISS
adjust BISS until you get the desired idle.

note: after turning the biss you’ll have to wait about 10-15 seconds to see the affect it has on the idle, the car is slow to react

once you’re happy, turn the car off and plug everything back in.

at this point though, it seems the best route would be to try someone else’s IACV or humour some of us on the board here and check for a vacuum leak… again… and again…

I had an intake manifold gasket leak once and I couldn’t see it / hear it / feel it because it was on the bottom side, lucky me I purchased a new one anyway and fixed the problem, otherwise I’d still be like you, at my wits end.

Sasha, the throttle blips you’re talkin’ about are for setting timing, the 3,4 3krpm blips cause the ECU to stop trying to adjust timing, it’s essential because without it you’ll set your timing, check it 5 minutes later and see that it’s totall off again.