A few days ago my Maxima started having an idle issue: it would drop below 600 whenever i took it out of gear (stick shift) and then pop back up to 600 where it should be.

The following day the problem manifested itself into a low idle (400-500) and a high idle (1000-1200). There seems to be no rhyme or reason to where it wants to idle. It also failed to start well sometimes. Every time it would start up and then die after a few seconds, to keep it alive I would need to rev the engine for a little bit. This issue happens when the engine is hot.

My initial checks: clean MAF, IACV, Replace air filter, check for vacuum leak. nope, no luck.

Shop says: its most likely your IACV is bad, however, when it goes bad sometimes the coolant can back up and short out the ECU. Said no one but Nissan can replace/reprogram an ECU

Nissan Says: IACV+ECU will cost $2000...wtf, not an option, I don't have 2k

Options I can see right now:

Step One: replace iacv and see if it fixes it self. should i get it new($200) or from a junk yard? ($40)

Step Two: Idle relearn, can someone point me to a guide if its possible? I've tried google searching but the only guide I found is for a 5th gen max

Step Three: Replace ECU. Can i pull a junk yard one or do i need to buy one? (they run about $300 from a auto parts store)

if someone can point me in the right direction on where to go with this that would be great, thank you! Please excuse if I broke any forum rules, i have done plenty of research prior to creating this post. Thanks!

Tim

 

There is no coolant near the IACV.
Coolant cannot back up into the ecu.
The 4th gen isn't the model year that burns the ecu when the IACV goes bad
There is no idle relearn procedure for a 4th gen
The ecu does not need to be reprogrammed for any sensor replacement on the 4th gen

Either troubleshoot the car yourself, replace the IACV or find another mechanic.

 

I thought if you did something with the tps while you turn the car on and off, it would re-learn the idle. I saw it in another thread, but they could have been wrong. I'm having the same exact issue. It occurred after my injectors went bad. I replaced all of them and the bad idle stayed.

 

Oh and I did all of the above that you did. Yesterday actually lol. But I also cleaned the throttle body

 

Thank you, I did not realize that. I was purely going off of what my mechanic told me.

So, next step? Biased off what the conditions I said earlier do you think the iacv is still the issue? I have a idle that can't decide where it wants to stay (only when completely warmed up im finding) and smells rich. Ideas?

Also, if I am to replace the IACV should I get one from a parts store? Any steps past replacing to cue the computer back to being happy? thanks again

also, how would I check if it is the injectors?

 

Start the car and get it up to operating temperature, drive it for 10 minutes.
Turn the engine off, unplug the TPS and restart the engine. Make sure all accessories are off, headlights, radio, A/C etc. The IACV will not be in operation at this point and your idle speed should be slightly lower then normal, 600-650 max. It should not hunt or misfire in any way, nice and stable, just slightly low.

If that indeed is the result, the IACV might be faulty. It the idle speed continues to change while the TPS is unplugged, chances are the IACV is not at fault and you'll need to do more troubleshooting.

If the idle speed is higher then normal with the TPS unplugged, make sure the cold idle circuit plunger and linkage is working correctly, coolant does flow through that device which is located down under and to the left on the throttle body.

If that's working correctly and the idle speed is still to high, make sure there are no vacuum leaks and I'll post instructions on setting the throttle body default idle speed.

 

Coolant temp sensor? Maybe the ECU "thinks" the car is cold when it's not. The rich smell and high idle when warm suggests that. If your cooling system hasn't been serviced in a while, go the whole nine yards, upper n lower rad hoses, thermostat, coolant temp sensor, and coolant.

I really really really doubt you have problematic injectors, and perhaps if you do, a solid romp on the highway, driving hard, should clear them out.

DW

 

Mine with the same problem finally threw codes! P0505 and P1400

Faulty IACV and maybe a faulty egr valve or clogged egr? Tomorrow I'm exchanging parts

 

yeah your mech is just wrong. There is no way for coolant to make its way back to the ECU lol.

If your idle is off, the first step is to troubleshoot the IACV and clean the TB and MAF. Check for vacuum leaks and hose tears. If none of those are your issue then check the TPS. If all that is workin then check plugs and coils and cranks and cam sensors. If all that is good, check and replace ECU.

 

My iacv was not working and my egr tube was loose. So maye check those. If not that, then our problems are just different? lol

 

IACV Check: checks out, runs high even when TPS unplugged

MAF: seems to be doing its job? cleaned it out, smooth when plugged in, terrible (with CEL) when unplugged

TPS: seems to be doing its job also? runs happy when plugged in, rough and terrible revving when not plugged in.

Emptied a whole can of starter fluid on the engine, no idle change, so no obvious vacuum leaks. (i made sure the engine was cool )


I'm going to clean out the egr tomorrow, but I don't think thats the issue. Have heard vacuum leaks can cause issues there, how can i check for those? Also, it threw SES/CEL for a bit and then it turned off, checked out P0505 when I brought it to a parts shop. this reads as idle speed problem. its getting to the point where i have to give it gas every time I start it to keep it alive and the idle is becoming more erratic.

ideas? should i just be bringing it to a shop at this point? any recommendations for a good nissan shop in the Denver, CO area?

thanks again

 

Are your plugs good? Are they NGKs? I had the idle drop problem, and replacing my old plugs with NGKs fixed it. I didn't have the high idle issue, though. You might have multiple problems. I was thinking vacuum leak too, although that will normally cause it to idle roughly and run like cr@p. Look at all the vacuum hoses you can find and check the ends for cracking, and check all the clamp connections on the air intake for starters. If you get your ear right down in there, sometimes you can hear the hiss of a vacuum leak.

 

My car just had the same problems except not stick and i put a TPS sensor in it last week and it runs perfect now. Mine was so bad it was throwing off all gear ratios and now i have over 100 miles on it and no cl. i would start there first because it is a lot cheaper then a IACV but that was just my experience with it. Does yours stall out?

 

It does stall out, but only on starting, not when running. However, it will dip down to around 300-400 rpm sometimes when you pull it out of gear (manual gearbox)

I just ordered a IACV today in hopes, my mechanic told me after he heard it die out right after i started it that he was pretty sure that was the cause.

TPS: any way to check it? i remember on my old honda there was a way to check if the voltages were correct at idle and wot, does the same apply here? numbers for correct wattages if so?

 

Yea it is all on this website http://www.vqpower.com/v2/articles.php?article_id=95. At the bottom it tells you how to test it

 

Thanks for all the help guys. I replace out the IACV and it works perfectly now. I'll keep the other check ups in mind in case I ever run into another idle problem.

 

On my '95 SE, I just started having the same problem as the OP and it only happens when the engine is warmed up.

This morning in fact, the CEL came on and it's the P0505.

I've had similar problems in the past where I've replaced the MAF (now on my 3rd one, with last being a $45 e-bay one), but the IACV is still the original, even though I took it apart and cleaned it last year.

Yesterday, after spending 2 hours in the engine cleaning every ground I could find, including under the battery tray, I started the car and then adjusted the idle (without unplugging the TPS), and took the car for a spin. It seemed to be riding better with a steady idle so I thought I had fixed the problem, however this morning, with the CEL coming on, I think it is either a vacuum leak or the IACV finally quit.

I have two questions:

1. Can a leaking upper intake plenum cause the idle to drop, or is it mainly the IACV that would be the cause? I ask because I smelled an odd smell (like burned oil) on Saturday after some spirited driving, and when I got home, popped the hood and found the plenum having a couple new wet marks.
   
   
2. Secondly, can adjusting the idle without first unplugging the TPS cause it to throw a CEL after the next two times driving it?

 

This may sound silly, but check how well your coil packs are plugged in. I had 3 work themselves loose somehow and the car ran like a Chevy Malibu, the new one.

 

After buying a new IACV and gasket online, I was in the process of removing the old one and found a loose bolt or two on the old one, and that the original gasket was reused when my mechanic did my power steering hoses the last time I had the car in there.

I then realized that my P0505 was probably due to improper reinstallation of my original IACV, by my mechanic.

I put my new one on, with the new gasket, tightened everything up properly, reattached the battery terminal, cleared the code and the car is good as new now.

So far it's been 3 days and no idle problems so I think the problem is resolved. It was strange that the idle was only acting up after the car was warm, but I figure the higher idle when the car is warming up masked the slight leak or perhaps only after it was warm, did air start escaping from the gasket where the IACV attaches.

Thanks for all your help, on this and many other threads, members.