My check engine light kept coming on & took it in & they say my idle air control valve is bad. They say they are not sure if it messed up my computer on the car. They also say they cant tell if it messed up the computer until they get a new idle air control valve & install it, then they will know if it messed up the computer. Its an expensive part, labor & part are like $527. If it messed up computer, a new one is like $1500. Do any of you know if they are able to tell if it messed up the computer as it stands now or are they telling me the truth when they say they cant tell till the new idle control valve is put in?

I just dont know if they are being homest. Anyone?

have you tried taking the IACV off and cleaning it???? Post a pic of your engine and I will help you with taking it off

The IACV typically takes out the ECM when it goes bad. They are correct in their diagnosis, as the only way to tell is to replace the IACV first. At our dealership, we price out both parts at the same time as the failure rate for the ECM when the IACV fails is in the high 90 percentages.

after he replaced the IACV how would he know if the ECM is bad, would the engine run bad or just stall out?

strange that a "flange" control sensor ruins your ECM, yaaaay NISSAN on that one(sense the sarcasm?)

Typically it would still throw codes related to the IACV unit. What normally happens at our dealership is the tech pulls the ECM and does the good old sniffer test. They almost always smell burnt, aka "somebody let the smoke out".

I have a 200 Maxima (GXE) and just recently had the IAC valve go and it DID take out the ECM. Today, I get the car back after having both parts replaced and as I'm driving off the lot, I notice the trasmission timing is off. When I step on the accelerator (about half-way to the floor), the car goes through 1st, 2nd, possibly 3rd, but then the tac just revs up to between 4000 and 5000 RPM before the 4th gear / overdrive FINALLY kicks in. When it does kick in, you can feel the bang and car shudders. Mind you, I'm not sure exactly which gear transition this is taking place at. It might be from 2nd to 3rd, it might be 3rd to 4th, etc. - who knows. All I know is that I never had a problem with transmission timing or slow acceleration before the IAC and ECM were replaced and now I do. Any ideas/thoughts on why I suddenly have a transmission shifting problem (i.e., shifting to a higher gear far too late)?

You are right CPS, they still have the car at the shop and at first thought the wiring harness melted or shorted out. After diagnosing it, they say wires are fine. They are looking deeper into it but say they feel its most likely the computer will need replacing. Not happy about that cause they are not cheap. The guy at the shop says they put in alot of used ones and it would be cheaper for me but how smart is that to do? Would not be cool to do that & it goes out in a short time as well. Where can I buy one at a good price?

Hey John Maxima, my maxima started doing like yours does, when I accelerate, it really winds out a long time before shifting. It has to be cause the computer needs replacing and thats whats causeing mine to not shift sooner, what you guys think?

A used ECU should be absolutely fine. That's the route I would take if I had to replace on. It's a solid-state electronic component, so "used" doesn't mean much. It should perform just as well as a new one.

Where do u buy the used ones & what can of warranty comes with it, probably none or very little?

Buying a used ECU is difficult to do, at best. Dealerships can't really help the salvage places, as the numbers that are on the ECU do not match up with the actual part number. The best option is getting the VIN's on both cars and having the dealership run them to see if the part numbers are identical. Also, most salvage yards won't give a warranty on an ECU because so many things can fry one, ESPECIALLY on a car where they know that one bad part can smoke them like the Maximas.

Yeah I heard its not a good idea. Well on Saturday I told the shop to just put in a new one. $960 part & labor. OUCH! They gotta have the dealership flash it & I'll be good to go.

I replaced the iacv on my 2000 I30T although it was not throwing up a code. The car will not idle when cold and Replacing it did not fix the problem. I already replaced the maf and the fuel pump. Is the ecm bad or is there something else wrong? when the car has reached normal op temp it idles and runs fine but when its cold it starts easily and then stalls in about 5 seconds.

Both the IACV and ECM both were bad and both replaced. Whether the car is cold or after being warmed up & driven, once its put in park, it slowly idles lower then car shuts off on it's own. It's back at the shop and they are still tryin to figure it out.

mrL wrote:Both the IACV and ECM both were bad and both replaced. Whether the car is cold or after being warmed up & driven, once its put in park, it slowly idles lower then car shuts off on it's own. It's back at the shop and they are still tryin to figure it out.

I know this thread is from 2009 but I have same problem as you.
Did you ever get it fix?
I have replace both IACV and ECM but kept stalling after start up. It start up fine tho....

PLEASE HELP!!!!

Anyone?????

What trouble codes do you have? Have you cleaned/replaced the MAF sensor? Did you verify the IACV is bad before replacing it and the ECU? It could be a bad engine mount (loud buzzing sound) which can also 'kill' the ECU.

Thanks for your help!

Yes, i have cleaned MAF. I had code for IACV and very same symtoms of bad IACV (higher idle and dies when engine cold) before i replace it.
I installed new IACV and ECU fixed by circuit board medic.
It starts up fine with no code then it dies within 10-15 secs. I have try to start it several times and still no code for ecl.
I can't even follow procedure for throtte position reset.


Any idea what i should look for please?
Thanks!!

You may have an intake/vacuum leak that gets worse when engine has warmed up. Check the fittings and tubing for cracks/loose connection all the way to the Throttle Body, as well as fitting between TB and intake plenum. You can spray carb cleaner on suspect area and listen for engine response. The Throttle Valve may be dirty. When was the last time you cleaned it. When cleaning, do not spray directly into the valve/body but instead into a rag then use it to clean valve/body. Have you used oil-based air filter? This can easily gum up the MAF sensor, intake and Throttle Valve.

If there is no leak and and Throttle Valve is clean, it could be the MAF sensor. The problem is that a marginal/failing MAF sensor will not give a trouble code and testing with DVM is not conclusive. An oscilloscope (expensive equipment) is needed to monitor MAF sensor response.