My 96 GXE threw it's first check engine light today at 116,000 miles. According to the friendly folks at AutoZone it returned two codes: Knock Sensor failure, and IAC valve failure. From what I've read the Knock sensor doesn't actually trip the light, so I'm assuming the IAC valve is the culprit. Shortly after the light came on I noticed that it was idling erratically / almost stalling when sitting at stoplights. Does this sound like an IAC-related problem? Is it possible to repair the existing IAC valve, or will I have to shell out for a new one? If it must be replaced, what's the best place to purchase a new one? Thanks for your help...

-Ace-

 

This was a coincident. I was hang around at my bro shop this morning, and there was a young guy pulled over with his superlow rider white Max. He described the problem that his car doesn't want to start, but when it started, it stalled like scrazy, idle gone up and down...then suddently it shook like hell. However, there was no check engine light. My bro ran a scan check, and there were two codes: Crankshaft position sensor and Idle Air Control Valve. He only replaced the IAC, reset the ECU and the car starts like normal, other code also disappeared. The List price for IAC is $171.67, but the shop only paid $120.17 as wholesale price. The Max owner paid $206.xx OTD.

 

IAC valve=idle air control valve. So it stalling while idleing would make sense. You may want to just try cleaning it (I think there are directions in the faqs). Also, even though the KS doesn't trip the light, you should still replace it. It gives better gas mileage and you will have WAY better performance.

 

hmm, if im correct the IACV is where the idle (black) screw is located...

with 114k miles (like me) i had to thoroughly clean it all out..TB, intake manifold, EGR system....etc...i never had that code pop up. but from what it sounds like your valve is stuck closed?

the culprit in this case, IMHO, would be the KS....a bad KS would cause you to run rich correct? running rich = carbon buildup correct? now, the IACV valve is basically part of the route that the EGR system travels thru. therefore running rich with a bad KS will cause alot of carbon build up in your EGR system, and in turn possibly cloggin up your IACV valve..

i would remove the whole IACV from the manifold (there is a gasget you might want to keep in mind incase you have to replace it, i didnt , but minez was in perfect shape..but i would recomend changing it regardless...) then after you do that...spray it clean with some TB cleaner..including the EGR tube while your there..

i cant remember but you MIGHT have to completely remove the intake manifold to remove the IACV but i dont think you do...

at your mileage, i would recomend cleaning out the Intake manifold and everything anyways...its a fun project and you will notice a difference like i did... then again my mom drove it like a granny for 110k miles...yea, thats ALOT of Carbon buildup lol...

try that, hope it helps

 

before you do all this tho, invest in a new KS....or else your gona be back there cleaning all that crap out again...

 

Is that true? I think the knock sensor only affects timing of ignition, not the fuel mixture - so I don't think it would cause you to run rich...

As for the original problem - as others have stated, clean out the TB, IACV, replace air filter, reset the ECU. Try to start the car again and see what happens. If the CEL doesn't light up, check for the KS code anyway (since it alone will not light the CEL). If the KS sensor code or the IACV valve codes reappear, you may want to replace both. The IACV is not cheap.

 

Unfortunately I don't have the $ for a new knock sensor right now, much less a $200 IAC valve assembly. I think I'm going to follow the directions at the site and try to clean it out real well. Hopefully after that I'll be able to reset the ECU and won't have it trip again.

-Ace-

 

Don't forget about the KS though, the light won't be on, but the code will probably still be there. Just replace it when you have the cash...you will be VERY happy you did.

 

Wow, I leave for a couple months and this place turns into a ******* newbie haven. My advice? Clean the Iacv and Throttle body by removing your intake assembly and the iacv, clean it ALL with tb cleaner, then reset your ecu, and drive. If either code comes back replace first the IACV, again reset ecu, and follow by replacing the ks if that code still pops up later.

Edit: I wasnt referring to you terran

 

I resent that; I've been a member here for almost two years but this is the first time my Maxima has ever had the slightest hiccup. Just because I don't follow these forums religiously anymore does not make me a newbie

-Ace-

 

Ok, I was worried there for a minute .

Anyway, so this post isn't a COMPLETE waste, you don't have to remove the intake manifold to remove the IACV. It's pretty simple. Oh yeah, this is probably in the writeup but when you take out the plastic adjuster screw to clean things, you should mark where it was so you can have some idea where to put it back to. I think I used a sharpy (permanent marker) on the metal to mark where the bottom of the screw was.

 

hmm, so you can remove the black screw while the IACV is still on? and spray tb cleaner to clean it out? or would this be a bad idea? im just curious...not that im gona do it.. i just cleaned it out lol...

as for my post...was it that unejumacated? i thought i did a good job tho, next time dont talk smack...just correct me im new with cars, i just thought i would share what i kinda know...no one else was posting.. i thought i would try my best to help him out..

what did i say that was incorrect? i would like to know, so i dont sound like an idiot anymore....

 

Well, I spent a couple of hours yesterday cleaning out the IAC valve assembly. It wasn't terribly difficult to get to but I'm not looking forward to doing it again. I reset the ECU and let it run for awhile and everything seemed ok. However, the CEL reappeared today with the same code(s). I guess it's time to start shopping for a new IAC valve. Can anyone point me towards a good seller? I may try to hunt around the junkyards first and look for a deal. Thanks for everybody's input.

-Ace-