Guys, i'm having funny idle issues. please help. here's the info and symptoms:
i have a '95 maxima, 5 spd, i had removed all the intake stuff for a temporary 00vi install which i took back all out, and put all the 4th gen stuff back in. the iacv connector harness i had to cut part of the plastic for the 00vi install, but it's plugged all the way in the 4th gen connector now and held w/ electrical tape. while the iacv was out i cleaned it w/ TB cleaner and also removed that metal cap on the inside. with that said, on to the idle issues...

after my car has been sitting for at least a few hours, like overnight or after work, i start up, rpms start @ 1600 or so, and while i'm driving around they'll drop down to 800-1000 rpm. a little off, but more normal than the next scenario.

after i've driven around, if i stop somewhere for a few minutes and get back in to start, the idle jumps up to ~2000 rpm. and it makes driveability really difficult. i recalibrated the tps w/ the car warm and the idle adjustment screw is in all the way and the lowest i can get the idle after the car is started when it's warm is ~1400-1500 rpm.

anybody else have a problem like this? i'm really baffled, but if i had to guess i feel like my iacv is not closing all the way or something when i start the car when it's warm. thanks and i really appreciate any advice/help.

 

as per the FSM:

"Here's the factory service manual component inspection procedure for the IACV-AAC.

1) Make this test with the ignition key OFF. Disconnect the IACV-AAC valve harness connector.

2) Looking into the valve connector with the latch at the top, you will see two rows with three terminal positions in each. They are numbered 1-3 (top row, right to left) and 4-6 (bottom row, right to left). Check resistance between the following terminals.
2 and 1.
2 and 3.
5 and 4.
5 and 6.
At a temperature of 68 F, the reading for all measurements should be approximately 30 ohms.

3) Reconnect the IACV-AAC valve harness connector.

4) Remove the idle air adjusting unit assembly (IACV-AAC valve is built-in) from engine. The IACV-AAC valve harness connector should remain connected.

5) Turn ignition switch ON and OFF, and verify that the IACV-AAC valve shaft smoothly moves forward and backward. If NG, replace the IACV-AAC valve."


-resistances came out fine. now when the IACV-AAC valve shaft smoothly moves forward and backward, how much is it supposed to move? mine moves a few millimeters at most.

 

so i took it out for a drive today. it drives just fine when it sat overnight, after warmup idle dropped to about ~700-800 rpm, but after a couple hours started it again and the idle never went below 1200 rpm. this is really bothering me.

 

Don't feel alone. I've had the same problem for a couple of months now. I've checked/replaced everything related to the idle air system I can think of (stepper motor, TPS reistance/voltages, fast idle cam adjuster) except the actual IACV unit, which I am replacing soon.

 

ya its a waste of gas right? did you check the IACV unit itself? how much does your shaft move in and out when you test it?

also, i might have a kink in one of the coolant hoses going to the throttle body, could that be a cause? it's a bend when the engine is cool, but i noticed that after it heats up, the hose gets soft enough to 'kink' and could blow coolant flow to the TB. also, maybe i connected my hoses wrong, but does it matter which way the coolant flows through the TB? thanks.

 

what's the stepper motor? i haven't checked that.

 

The this weird lookin metal/plastic piece above the intake manifold. I believe one of the hoses connects to the intake manifold and another connects to the black plastic EVAP thing. It is bolted onto the intake manifold via two 12mm nuts that I normally remove in order to remove the last coilpack in the rear bank.

 

oh i have a '95. i think either i don't have it or its not in that location.

 

More reason for us to believe that is not the problem

 

ewuzh-

so you have the same symptoms as me? it drives fine when it's been sitting for a long time (like overnight), but upon startup when it's been recently driven, the rpms startup to 2000 and drop down to ~1400-1500 even though the engine is already warm. and my idle remains high.

when did you first notice this problem? b/c for me, i took out my intake manifold, temporarily put in a 00vi, and then put all my 4th gen stuff back in. then i started noticing this problem after that. initially the 2nd startup would cause idle at around 2000 rpm, but after turning the IACV adjustment screw all the way in i brought it down to a more reasonable ~1400.

i don't want to think it's a vacuum leak, b/c then i would have this problem on initial startup, but i don't.

 

It started happening after I removed my supercharger. I also removed the intake manifold to replace my injectors, but that was after the problem started happening.

Yes, mine idles at 1500 and surges to 2000 when warming up. When it's fully warmed up it idles at 1500 or sometimes goes down to 1100 occasionally when it feels like it. This is with the IACV adjustment screw all the way tight too.

I think it could be a vaccum leak, but theres so many vacuum lines I wouldn't know where to start.

 

so you think it's a vacuum leak? i don't know what could possibly explain why we don't have idle issues when we first start up after the car has been sitting, but then after starting again have a high idle?

if it were a vacuum issue, i suppose after the temperature in the engine bay increases and the hoses become warmer, that could change the properties of the hoses and possibly leak, but i don't know how likely that is.
then again, the problem we have does not seem to be a common one.

 

so i got a hold of 2 extra IACV's (1 off a 95/96, 1 off a later model 4th gen) and i'll try them out tomorrow.

 

ewuzh-

this is aznsap. we tried out a different IACV and the problem is still there. so i doubt its IACV related. i may be thinking this is a vacuum leak after all, possibly my egr guide tube isn't in tight enough.

 

Im throwing a code for my IACV so I will be replacing it anyway. I hope I can find the vac leak. Actually, my vac reading at idle a bit lower than normal (15hg).

 

so i tightened up my EGR guide tube, and i still have the problem. we heard a noice coming from around the rear of the intake manifold, but we're not sure if it's normal or not. my guess is if it is normal, it's just the sound of exhaust gases going down the headers, but it doesn't sound like a vacuum leak.

so now i'm really confused.

 

Let the car warm up and then disconnect the TPS and WOT switch(some 95's only have one connector) Rev the car some, where does it idle?

 

it idles at around 1400 (as in... the idle doesn't change with the tps removed or not). the TB plate is fully closed as well.

since i replaced my iacv, i think i can rule out IACV or TB for now. the high idle must mean there is air from some source other than the TB or IACV. but only on warm startups. i do not hear any vacuum leaks, so could the EGR be a source of the excess air?

 

UPDATE: Problem fixed. Change your PCV valve.

Frankly, I am very surprised. I figured this would be a long shot, but my idle now sits at a perfect 750. Last time I changed it was only 10,000 miles ago, but when I took it out today, it was dead already (didn't make any noise when you shake it).

 

Lol really? PCV fixed it?
Are you using 5th gen or 4th gen valve cover?

 

Stock 4th gen VQ30DE.

 

How did you do your setup? When I had the 4th gen VC, I had a PCV that had an L at the top.

 

It's a straight PCV valve. Looks like this: =|=

There's a rubber hose coming off the other end that curves to clear some hose (EVAP/idle air stepper motor, IIRC)

 

are you serious?!?! mine still made noise when i shook it in a side to side direction. wait, how can that explain why it idles high on warm startups but not on cold startups?

and what kind of pcv valve did you get and where from? how about the 00vi guys using the 4th gen lower, where did you get your pcv valve from?

 

Nissan parts wasn't open on Sunday, so I got a cheapy autozone PCV valve. Looks cheap and was cheap, but it worked !

 

i am so confused and the symptoms we got though. so you had a normal idle on cold starts, but when restarting it idled high, correct? how does a bad pcv do that?

 

probably vacuum leak by the top of the 4th gen valve cover pcv hole.

here's how i set up the rear valve cover.

I also use the 5th gen/PF iacv.



here's the thread its from: http://forums.maxima.org/showthread.php?t=477210

 

Mine had nothing to do with starting really. On cold starts, it would idle at 1500 and occasionally surge to almost 2000. When fully warmed up, the idle would not go lower than 1200, usually idling at 1500 still. On warm starts, it would idle at 1200~1500 also. Using the Haynes and .org stickies method of adjusting the idle, I could not get it to idle lower than 1100 with the TPS disconnected and the IACV adjustment screwed all the way in!

 

hmmm, i have a different problem than you then. my idle will be normal ~750 after the car is warmed up after it has sat overnight. but if i shut it off and start it again within a few hours, after it's warmed up it idles high 1200-1500.