Just bought my 2nd Nissan ever an 01 Maxima GLE with 185,000 mi. I checked the codes when I got home and have:
P0505 IAC circuit. Ihave read up on this. ECM or the IAC asy.
p0140 Bank 1 sens 2 02 sensor
p0160 bank 2 sens 2 02 sensor
I have seen on several car where it will throw certain codes together even though they "may" not be related. I would hate to think I would need an ECM. I read the values on my antique scan tool and they look normal to me. Any other suggestions other than ECM replacement? If so, where is it? I see most people just replace the o2 sensors for their codes. Thanks for the help!

 

Doubt they are related, you probably have a bad IACV and an ECM with a burned out STA509A mosfet. If you do it yourself you can repair both these for about $150, maybe even $100 as some have used non-OEM IACV's from eBay with success. I'd fix this first, then the O2 sensor if you still have a code for it.

 

Follow Pilm's advice. If the IACV is bad, the engine isn't necessarily getting the correct fuel ratio, causing O2 codes. Resolve the P0505 and there is a good chance the O2 codes will go away.

 

I took off the pos terminal cover and found the big, green fuzzy monster under there. Cleaned it up and reset the codes. All the codes went away but the P0160. I cleared it and so far hasn't came back. Probably have to replace that o2 sensor. It still idles up and down between 1200 and 1400 rpm when hot, but not listing the code.

 

She should idle steady at around 700 RPM. The 0505 code is usually thrown when the EMC gets fried. It is possible to have an IAC on the way out that will cause the eratic idle without frying the ECU. The ECU gets fried when a coolant leak in the IAC shorts out the mosfet. There are other failure modes of the IAC (bad stepper motor) that will not fry the ECU.

I have experienced both (different Maximas - I used to own 2). When the ECU goes, you will smell it and the P0505 code will set off CEL

 

I am really getting under it today to service it. I looked at the IAC and it appears to be really new. I cleared the codes and both o2 codes came back. I was wondering if the rattling noise I am hearing is a piece of broken cat converter falling and plugging the exhaust partially. It doesn't feel like it slows it down. Might need both sensors. Are you talking 700RPM in gear? It does that, but not when it is in park. It surges while in park.

 

RPMs should hold steady at around 750 while in Park and around 700 while in gear. If IACV is workin properly, there won't be any surging