I can't really afford to replace both right now, and I know that if you have a bad IACV and put a new ECM in it will fry out the new ECM immediately. I just didn't know if it works the other way around.

Also, I plan on sending my ECM out for repair rather than replacing it. It's much cheaper and I really don't feel like hanging out at the stealership. Would I still need to have the dealership reprogram it, idle relearn, idle air volume, etc. on it? I'm just really confused about the order of which everything needs to be replaced and relearned and s h i t.

 

I've read where some people claim a bad ECU can damage a new IACV, however I don't believe it. If the ECU mosfet is blown, it won't step the IACV motor since it's dead, so the worst thing I can imagine is the IACV can't be adjusted and your car won't idle and will just keep dying at start up like it does now. That said, it's never a good idea to do half a repair job since unintended things can and do happen. And really, what's the point of replacing one before you have the other, car still won't idle, so you are just asking for trouble.

When I had 505 code, I replaced the IACV with an OEM part from an eBay Nissan dealer for $130. I also bought the STA509A mosfet on eBay for $15 and replaced the blown one in the ECU. I didn't have any damaged traces, so it was a simple part replacement. If you have blown traces you will need to add jumper wires, which in itself isn't hard, but you'll have to ohm the circuit out to make sure you fix all the blown traces (should only be the 4 mosfets output traces at most). I would never buy a new ECU, cost is ridiculous, and if you can do some basic board work (solder, probe, etc), you can save a few hundred by fixing the board yourself. Anyway, once I replaced the IACV and installed the repaired ECU, car idle at turn on was already correct, so I didn't need to do any idle relearn. It's only a guess, but my guess is that as long as you replace with an OEM IACV and fix your current ECU, then you probably won't need an idle relearn (the old settings in your ECU will still work fine). I think people who have idle problems after repair either have another problem still going on or they used a new ECU that doesn't have your cars old settings, so new ones need to be found by doing the relearn. It may also be that an aftermarket IACV is sufficiently different than an OEM IACV that a relearn may be required. But like I said, I think if you repair your ECU and use an OEM IACV, you probably won't need a relearn.

 

^^^ what he said.

I have to assume that you had the P0505 code. Did you (or someone) check the resistance readings of the stepper motor coils to verify that the IACV was bad? If you had the code, it most likely is, but you should verify.

 

You are legendary. I've been trying to get information like that from someone for months. Thanks so much for the help.

If you don't mind, who was this OEM dealer on eBay you found the IACV for so cheap? I was going to RockAuto for mine for a little bit higher price, but I'd rather get a dealer part in this situation.

I took it to the stealership and they gave me a whole list of s h i t that was apparently wrong with the car. The IACV/ECM issue, then some other crap about a bad cat and gaskets and marker bulbs in my doors and ignition coils and a bunch of other minor stuff. I don't trust them, but if the motor mounts were bad they probably would have told me and listed it with the rest of the problems they wanted to fix. I also heard that if the motor mounts go bad, you'll hear a fairly loud buzzing noise from under the hood after releasing the gas pedal.

 

Just open up your ECU and see if it's got a fried STA509. There is a videon Youtube.com that was put on by FIXINGYOURNISSAN and he goes through the steps. He also claims that you can't have the ECU repaired but that's B.S. My ECU was repaired. Just make certain your board isn't s hi t housed with holes burned in it or they WON"T be able to repair it. I used DAT in Corona, Ca. They did a good job and it was 200 bones. Also, I checked out a couple of the chinese offerings and they were crap. Way high and way low resistance readings right out of the box! Buy Nissan.

 

Electric motor mounts are not consistent. They will sometimes make noise and sometimes not. The noise can even be heard after you turn the engine off, if it is going to make noise. If the little electric motor keeps running, which is the buzzing noise, it can cause one of the STA509A driver transistors to burn up, similar to the IACV shorting. The motor mounts can also split open allowing the oil to pour out but this won't damage the ECU.

 

Here's the one I bought: http://www.ebay.com/itm/Nissan-Maxim...d278d8&vxp=mtr

$139 shipped, also comes with a replacement gasket. Just make sure your MFR date is between 4/1999 and 6/2001, or you might need a slightly different model. Looks like this isn't a Nissan dealer after all (aiautoparts), but it is an OEM Hitachi part that I got, I'm sure of that, and most importantly it worked.

 

I'm sorry to revive this thread again, but here's my situation. I can remove the ECM and have a new chip soldered on to it, BUT before I do that I need to replace the IACV. I have a local shop that'll do it for me (I ordered that part from the link provided), but will the car be safe to drive with a new IACV but a bad ECM? Atleast until I get the car home and then remove the ECM and fix that. I just don't want the new IACV to fry because the ECM is s h i t. Some say that it will, some say it will not.

So the question, will a bad ECM fry a new Idle Air Control Valve? I need a response from someone who has actually done this job and is speaking from experience, not just going from some rumors. I really don't wanna be **** out of another $200. Yes I know it's gonna be a half-done job, but I HAVE NO CHOICE but to drive it to the shop and back with a bad ECM.

 

Probably not. If all four ECU mosfets are blown, then they are dead and they can't hurt the new IACV. However in reality you probably have just one blown mosfet that failed when one coil in the old IACV shorted. So what you'd have if you put a new IACV in is 3 good mosfets driving 3 good IACV coils, and one blown mosfet not doing anything to the 4th good IACV coil. So I'd say it's very unlikely you'd damage the new IACV. Think about it this way, before you replaced the old IACV, you were already driving the car with 3 good IACV coils (only one was shorted) and 3 good ECU mosfets, and this was ok, that is, the good coils didn't cause the good mosfets to blow, and vice versa. So the only thing that changes with putting a new IACV in is you now have a good coil mated to a blown mosfet, but as I said, a blown mosfet doesn't do anything, it's like having an open circuit. Now all that said, I still wouldn't do it because there is always some risk operating a car with a damaged computer, and also because I just don't see the need. I would have the ECU fixed first, install it, but leave the IACV connector unplugged so the repaired ECU can't drive the IACV and get redamaged. Then drive to the repair shop and have them replace the IACV and reconnect the IACV connector.

 

Hoping someone can help...2001 maxima is at the dealership and "requires iacv and ecm". I took the ecm to be refurbished and was informed there is no apparent damage, the board looks pristine. Dealership states pin test showed ecm detects no voltage from battery. Is it possible the dealership is mistaken about the ecm needing replacement? Could this reading be the result of something mechanical needing fixed along with iacv? Appreciate any insight available.

 

You have yourself in a dilemma. You have 2 repair shops telling you opposite things. Unfortunately there is no way anyone on the org can tell you which one is right and which one is wrong. We don't have your ECM.

About all you can do is take the ECM to a 3rd place and get their opinion.

 

Thanks dennismik, it is a dilemma! I am guessing that from your response, you cannot suggest another reason for not getting voltage from the battery on the ecm...I should have also mentioned that the car was drivable (although the rpm's were erratic) going into the shop and that they also suggested replacing the battery.

 

Hello, CAN I DRIVE WITH THE IACV VALVE UNPLUGGED? I replace the ECM and I got a full throttle control body from a junk yard but it seams that the valve is not good here either. however, the engine light did not turns on but the scanner gives me the code P0505. it could be that the ECM is good or bad, I don't know, I think that it is good because of an early discovery. the car is parked now but at this point I only want to drive the car until I replace the Valve and figure out what I want to do. So, can I without braking the new ECM?

 

Yes, you can drive with your IACV unplugged; your engine might idle poorly, but you should be able to drive.

However, your description above suggests that you just installed a "junk yard" TB and IACV, and that a P0505 code is pending. If this IACV is bad/shorted (as the P0505 suggests), then it might have already damaged the transistor drivers in your ECU. On the other hand, perhaps it didn't ....

In either case, disconnecting the IACV is you best immediate solution.

Next, you need to find out whether your ECU is damaged. Remove it and inspect it for damage/burns (to find out how, search for "ECU" or "fried ECU"). In the event the ECU is damaged, do not install a replacement ECU before replacing the bad IACV!

To replace the IACV, you can buy an OEM part from Nissan at ~ $250, or an after-market part for ~ $65 (from eBay, AIP electronic). The consensus on this forum is that the OEM part is a safe bet (it will last ~12 years), while the quality of the after-market part is unknown. (There are one or two reports from members who used the after-market part for 2 years without problems, but no reports of long-term use).

Hope this helps.

 

I drove 6 hrs from FL (where it had failed on the road) back to GA one night with a blown ECU and IACV, so yes it's possible. I keep a code reader in the glove box, so I knew the deal as soon as it happened. Like you, I pulled the IACV harness (hoping I could possibly save the ECU) and limped it back home. Of course when your on the gas all is normal, but for stop lights, braking, and coasting at idle it was a long battle of shifting back and forth from drive to neutral (to stop the transmission and brakes from fighting each other). There are numerous threads on this issue on these boards, read them all and get it fixed ASAP, b/c this problem is just going to drive you MORE crazy the longer you wait...

 

If I replace the Idle Control Valve do I have to replace the THROTTLE VALVE SWITCH too? and if yes why?

Thanks

 

No, you don't - unless there is something wrong with it.

 

Hi, and first, thank you, this is a great thread. I just put in a junkyard iac but have not reconnected my ecm because I'm afraid that the ecm may have gone bad when the iac went out. There is no sign of damage inside of the ecm, and I'd rather not buy one if possible. Is there a way to test the part of the ecm that would have been damaged by a po505 issue? If the new iac is good and the ecm never took damage is it still necessary to perform an idle relearn?

 

if you don't have any visible signs of damage and it passes the smell test i'd say you're good to go

don't worry about the idle relearn, if your battery has been disconnected it'll take care of itself

 

+1! - on both counts.

 

I never disconnected the battery, will I want to before reconnecting the ecm? I didn't see anything about it on the 6 part YouTube video. Thank you!

 

it wouldn't hurt anything to disconnect it and would force a "relearn" if needed, though i suppose disconnecting the ecm has the same effect. idk if it's necessary but i've been in the habit of disconnecting the battery before i start pulling and plugging connectors, in this case i guess i assumed it had been taken out since you need to pull the airbox/etc to get to the iacv anyways.

 

The problem is persistent, with the replaced iac (black connector only) it seemed to be fixed for about 10 minutes and then reverted back to the usual up and down idle while in park. Is it necessary to take the whole part out instead of just the connector? I know it's possible that there is a vacuum leak but everything I've taken out of the car in the past 3 years has had flawless seals and grommets so I'm trying to work around that idea

 

not sure, i replaced the whole part when i did mine

 

No, it's not necessary to replace the "whole part" (this is from a Nissan tech I talked to). Did you tighten it right? Also, did you disconnect the battery overnight, not just for a few minutes?

 

I went ahead and replaced the idle valve and manifold new but I'm still getting the same problem, tested resistance on the junkyard valve as well and it's still good so I know they're not being blown by the ecm. I'm now looking at ecms out of desperation although mine still looks and smells fine, I'd like to go junkyard but at autozone they told me that I need to get an ecm that either has or doesn't have traction control, there doesn't seem to be a standard for the i30, can anyone tell me how to know? By looking at the ecm maybe? I never disconnected my battery because I used it to rest my air intake on, it is reading 12.9 v, do you think this could be significant?

 

i would try the battery first for the air idle relearn. disconnect overnight, maybe flip on the lights to get all the ghosts out. check in the morning for happier days

 

I hate to say it but I took the Infiniti to the dealership, they confirmed that it was the ecm. They tried to charge me 1300, So now ecm is on its way to circuit medics who have a 5 star rating and excellent reviews for 200. I'm just hoping that the new iac is not blown from the ecm, I hooked up the junkyard iac, that I tried and ran the car on as my first attempt, to a power supply and the plunger still moves when given volts, do you think this could be an indication that the problem effecting my ecm does not hurt the iac?

 

Search this forum for references to Circuit Medics. I haven't seen too many good ones. It's probably too late, but read the last section of this document: https://drive.google.com/file/d/0B6O...1fNlF5QjQ/view .

Re. the ECM hurting IAC: As a rule NO (it can't hurt the IAC), but you can't completely eliminate the possibility. For example, if the ECU is damaged so that there is a permanent short (like, melted solder on tracks, etc.) it could damage the IACV. That's why, if you want to be sure, you replace both at the same time.

 

Hey guys just posting my conclusion, the repaired ecm was able to be programmed and I did not have to get my keys reprogrammed, I installed the new iac before driving to the dealership on the faulty ecm, iac was fine. I was then able to pull, send out and reinstall the repaired ecm in the dealership parking lot. Got out of the whole thing for about $600, but you could probably do it cheaper knowing this info. Big thanks to everyone who responded!

 

Looking for a little help. I have replaced the IACV and TPS sensor and had the Mosfet replaced by a reputable repair service. I just installed it all, and still have a high idle. It still stores the code also. Acts as if I had done nothing. What am I missing?

 

I had this happen to me when my p0505 fiasco was going on. I had my ECM repaired by a shop (Circuit Board Medics). IACV replaced, all wires/voltages/resistances checked and double checked. Spent many long days trying to figure out my issue when I finally broke down and took it to a dealer. They hooked it up to their Consult II diagnostic computer and it showed the ECM was still faulty after the repair. Not saying this is your issue, but I can tell you from first hand experience that it is possible. Are you hearing any sounds/movement emanating from the IACV at all after start up? You can always pull the IACV and check the resistance of the proper pins if you question its functionality and rule it out as being the culprit. If it checks out good and you are not getting any sounds/movement from the IACV I'd start thinking about the questionable repaired ECM more.

 

What code are you talking about?

If its the P0505 code, this means a bad circuit from the IAC to the ECM. Don't mess with the cheap IAC brands like the ones from Ebay(around $30). Go with the OEM Hitachi IAC(around $130). But its more than likely that your ECM is still bad. You need to get it checked again I'm afraid.

 

UPDATE: So after I drove it the first time and still experienced a high idle. I let it cool down about an hour and started it again. This time the idle was much lower. (Original symptom was a very high idle and tough to keep running when cold) Took it on another test drive and idle settled down to around 700-750 in gear.

Maybe it had to relearn its idle?

And yes I simultaneously had the Mosfet repair, IACV, and TPS replaced. I looked at the board and the Mosfet had no damage. I had even order the Mosfet as I have decent soldering skills, but after looking at it, decided not to risk damaging the board with my shaky hands.

No P0505 code pending after 3 warm up drives. I think it is fixed.

 

Yes, it has to re-learn but usually you just disconnect the battery overnight and that does it.
BTW, did they tell you why you had to put in a new TPS?

 

Those cheap 30-40 ebay iACV ARE THRASH! One of them burnt shorted out my perfectly good ecu..

 

No, just everything I read said to replace it, including the board repair facility.

 

All of those ECM repair shop's say the same thing, "replace IAC, repair ECM and change TPS". Its like all of them are working with each other or something. I found it weird actually. And they are making a fortune from consumers bad luck.

But the TPS has nothing to do with the P0505 code. The repair shop that I took it to also told me to change the TPS. I did the trouble shoot and the TPS turned out good. So you more than likely paid for a part that you did not need. A shop can't tell you to change parts when they haven't even done testing on that particular part. Not all problems are similar. Just like how some didn't have to repair their ECM even when they had a faulty IAC.

 

Just wanted to update and let you all know that the P0505 code is officially gone. Thanks for the help!

 

How did you fix the problem? Maybe others can benefit from your process.