MaxGearhead

Just bought a 2001 SE 20 AE 5 spd with just only 91k in great shape. A week after I bought it, it stopped idling. Would start but would die if you took foot off gas. P0505 error. Replaced IACV with an AM-Autoparts unit and now it idles but always around 1300-1400 RPM. Also seems to run lean right after a cold start up and has an abrupt off/on throttle effect. Still showing P0505. Before I repair a suspected fried ECU, I decided to take to Nissan dealer to test ECU. Here's where it gets confusing. They said they needed to do an IACV relearn and had to do it when the car was cold (I have never heard of this). After having the car there for a full day, they said the relearn wasn't working and suspected a bad IACV. I have never heard of this relearn procedure. Of course they want to sell me a $379 IACV and if that doesn't work they want to hit me with an $1100 ECU. Any advice?

maxiiiboy

First, read the document about ECU Failures (link in my signature).
If you indeed do need another IACV, don't buy it from the dealer. Buy it here: http://www.rockauto.com/en/moreinfo....374533&jsn=449 - only $110.00 for the OEM part. Good luck !

MaxGearhead

Thanks- the first thing I did after getting the car back was to purchase a Hitachi IACV just to rule that out. Still surprised that the dealer was not able to give me a conclusive diagnosis on the ECU. If that doesn't work, will pull the ECU out and possibly have it rebuilt.
My question still is- Is the re-learn process necessary? It seems most of the reading I have done on it points to replacing the IACV and then the ECU to solve the problem and never mentions a relearn after IACV replacement.

maxiiiboy

I have never done a re-learn. Not even when/after I replaced my IACV.

MaxGearhead

Replaced IACV with a Hitachi unit from RockAuto. Now it has a high oscillating idle (1500-2000). Still have a P0505 error but not sure if my scanner app is working properly. Going to try to reset ECU and see if that does anything. Will pull the ECU next. This is frustrating.

maxiiiboy

If you still have P0505: Make sure that your ECU is not bad, and that it's not repeatedly killing your IACVs (you've read my document, right?). The only way to find out is to pull the ECU, and check it out (sniff it for any burnt smell). This whole issue is a PITA.

MaxGearhead

Yup. ECU reset didn't work. Pulling the ECU next. Still baffled why the Nissan dealer couldn't tell me I had a bad ECU.

maxiiiboy

The ECU is a computer. To fully test it (or any other computer) is not easy. However, in most cases of P0505 the damage is limited to the failure of the IACV driver-transistor.
Edit - one more thing: Make sure to clear the code(s) before attempting the re-learn.

MaxGearhead

Did the TB coolant bypass and sent my ECU to Module Repair Pro to get it fixed. Got it back and installed. No more error code and the idle is controlled but still idles high. Adjusted it down as far as it would go on the stop screw but it is still around 1100 rpm when warm. Is there something else I am missing? Could be a vacuum leak but I have no other symptoms of a vacuum leak.

Whostheboog

The new Iacv has to be put in with the new/ repaired only and vice versa of course. If the Iacv was in contact with the unrepaired ecu its already bad, if it's already bad and you put the repaired ecu in, it's already bad too, and even if for some reason it isn't the case treat it like it is because this can be a vicious cycle that can easily be broken. It can also if not done properly cause you to part out, scrap, or leave in a bad neighborhood with the door open, and running. Idle relearn is also more necessary than you guys have mentioned. Our tachometers are slightly off and even then our cars may idle fine after the repair Glee did. When I got my datascan 2 she was idling around 670 I believe it was either low or high but I'm pretty sure 670. When I did idle relearn she holds 712 725 712 725 consistently. When I advanced my timing 2° she went up a little bit did relearn and back at 712 725 712 725. Still holding the timing advancement too. Funny thing is even though every time the idol strayed high or low it was still technically in tolerance I can vouch that the idle relearn process puts it where it needs and wants to be. The idle when high and low was in limit, consistent and felt missy. Relearn does something I haven't figured out or learned about that puts it not only at the correct rate but sinks at together...

MaxGearhead

I disconnected the new IACV until i got the ECU repaired. Put it all back together. When cold, fast idles around 1500 and settles to about 1000 when warm. Tried the idle relearn and it didn't seem to make a difference. No error codes. Seem to run lean right after a cold start. Might have a vacuum leak? Noticed the IACV connecter showed some small signs of plastic melting but not enough distortion affect the contacts. Am going to look for one at a salvage yard just in case since they aren't available from the dealer

cornholio

iTrader: (1)

Also check the accordion boot coming off the tb for cracks, the rubber gets old and brittle and it's easy to tear (especially when you start messing in that area doing iacv repairs).

cdoublejj

Don't have to time to read so blindly copying and pasting in the chance any of this info helps anybody. SORRY

I'm assuming we are talking about the IAC and thusly the idle circuit.


I had a high idle and VERY clean ECU. Sent off to a an Ebay "service" seller that i trusted and lo and behold it did have circuilt damage. while waiting i learned that the Throttle Position Sensor and IACV were on the same circuit!

So i bought i OEM TPS and a proper IACV and i got my repaired ECU back. My throttle body didn't NOT have flat surface for the IACV to mount to. I had a skilled mechanic true the mounting surface for IACV before mounting. He also used an addition compound to aid the sealing power of the included o ring type gasket which NOT advised.

I've not had any problems with the throttle circuit since. Why this info in pertant is because of all the ignorant people who replace the same 3 parts several times! The IAC can foul ECU and the TPS and the fouled TPS can fouled the ECU or the IAC and the fouled ECU can fouled the TPS and or IAC.

and that's why it's said to replace both and have the ECU checked out and if needed repaired by a professional.

doublea

iTrader: (7)

That mayy explained why I have had so much trouble starting my engine. First time I start it the idle was shooting all over the place. When I tried to re-start the engine with a new IAC valve I couldn't start the engine, so I had the ECU rebuilt. When I got it back the engine refuse to start, so I swap both the ECU and the IAC. I now just have to fix the adjustable fuel pressure regulator and see if I can start it back. So are you saying that the fried IAC also kill the TPS and both can trigger the ECU to fail ? The TPS has both connector on it right ?