sublunary

iTrader: (2)

i have been having a frustrating time lately. i failed emissions about 50 days ago(60 days coming soon), my abs went out and twice in the last week i have gotten stranded because car wouldn't start. first time i eventually got it started but last night i had to get it towed(first time i've ever had to do that). i had a code 21 and went through the diagnostic #27 in my fsm and everything checked out. then i tried to start car this morning and it started but with high idle (around 1200) which didn't go down even after it warmed up. i thought at both times that it wouldn't start that it was not getting spark but that was a guess. i feel like i have checked every thing i can and i am running out of ideas
i have the three front coils and a new o2 sensor coming in the mail but i did the o2 diagnostic and was getting more than 5 flashes in ten seconds so i don't know if that will help but i have never changed it so i hope it will help the smog retest ( i barely failed for nox and HC)
sorry for the wordiness any suggestions would be appreciated in the meantime im reading fsm and drinking some more i guess...

92 Max

Sounds like a bad connection somewhere in the coil circuit or ignition resistor. Or possibly a bad ecu relay?

sublunary

iTrader: (2)

yeah i checked the ecu harness for bad/bent/corroded pins and got continuity everywhere between ecu and coils. i am wondering if the power transistor could check out but fail under load or when heated up? even as i say that i don't believe it. things should either work or not in a rational universe.

sublunary

iTrader: (2)

im now thinking it may be the something with the IAA. the diagnostic (in the EF & EC section of the fsm) for high idle says to pinch the iaa hose (the big one coming off the top of the TB) that isn't really possible so i just disconnected it and plugged the hole to the TB and the car wouldn't start in the same way that it wouldn't start when i was stranded (if that makes sense)
the fsm sas that if pinching hose (cutting air to the IAA) causes engine speed to drop then check IACV regulator, IACV valve and circuit. i checked the valve resistance and its ok. i still need to check the plunger and spring.
so now im thinking that if something is wrong with the iaa it could be intermittent and that could be an explanation of what has happened.
any feedback?

Greeny

iTrader: (43)

Try cleaning the iacv.

sublunary

iTrader: (2)

did that within the last couple years but i think i will have to take it off to check the regulator so i will spray it out again. the regulator has a wax piece that might explain the intermittent nature of my problem. i wonder if i will have to get that from the dealer if its bad.
in order to apply 12v to the iacv solenoid to test it, can i just jump two wires directly from the battery?

Greeny

iTrader: (43)

you are better off finding a good unit in the classifieds or the j-yard,the iacv is sold as a one piece unit and is extremely expensive new,even from autozone/advanced/etc.(about $160)

sublunary

iTrader: (2)

yeah i just saw that on the autozone site. but i might rather pay that and not have to worry about the used one going bad and waiting to get it mailed to me. ready for this...my max is my only car, i got rid of my work van and take the subway to work so when the max goes down my wife has problems getting to work. she's not nearly as affectionate toward the max as i am so there's some tension if its not running right away...

Greeny

iTrader: (43)

Ahh,ic...I would love to see the dealer price..

sublunary

iTrader: (2)

oh no, im not buying it at the dealer since i can get it at autozone. but now im having doubts about it being my problem. i mean sure the high idle would be because of the iacv but if it was completely messed would the car not start at all?

i just thought of something that i might have got wrong, when i ( in post #4) plugged the hole in the tb i should have also plugged the hose to the IAA so i better go do that before i draw incorrect assumptiosns

sublunary

iTrader: (2)

this thread is going to become luke's diary of a car problem
anyway i tried and yes the car won't start with the air blocked to the IAA but i'm not sure that a bad IAA will completely cut off the air like i did to test, so i am not convinced that a bad IAA is causing my "not starting" problem

internetautomar

iTrader: (30)

coolant sensor maybe?

sublunary

iTrader: (2)

brand new...
btw, car started fine today no problem, so that sucks because maybe the stuff i am checking fails but is ok at the moment i check it

sublunary

iTrader: (2)

yeah i can't find anything wrong with the IAA. i did the hot water test to see if the wax/piston worked and it seems fine so it is back to the beginning

92 Max

Again it's possible it's the ecu relay or the coil relay on the other side. These may test out O.K. per the FSM and still be bad (mine for the fuel pump did). Try and find another relay of the same color elsewhere in the car and swap them. If the problem travels with the relay, that's it. Or just buy a new one like I did and see if the problem goes away. They're about $20.

LvR

Dunce (me) here ................

Can you explain the method and conclusions you reached?

IAA = IACV yes? ................. if so its surely servo motor controlled from the ECU and doesnt rely on "wax" (either its properties or presense) at all.
If the IACV/ECU is working as per spec, the IACV's valve sits about midway of its possible travel in order for the ECU to be able to control idle speed efficiently - thats why if you pinch the hose, the revs should drop - the IACV supplies the part of the engine's idle air requirements that the TB cannot when its at rest.

sublunary

iTrader: (2)

the fsm uses Intake Air Adjusting unit to refer to "unit made up of the IACV-AAC valve, IACV_FICD solenoid valve, IACV-air regulator and idle adjusting screw." i was just using their terminology but i guess most people just say IACV for whole thing. like "transverse link" instead of lower control arm. almost all my mechanical experience is from working on my maxima so sometimes i don't know what the more common terms are.

as far as the hot water thing, there is a piece of wax in the air regulator portion of the iacv that expands as the coolant, that runs through it, heats up. that pushes a piston that cuts off the additional air that allows for the higher idle speed at warm up. so you put it in hot water to make sure the piston still closes. if not, that is the cause of a high idle after warm up.

now there is ecu control of other parts of the iacv like the IACV-FICD solenoid which increases idle when A/C is switched on, and also the AICV-AAC(aux. air control) valve.
and as to the pinching the hose, the diagnostic says to pinch the hose and if engine speed drops than there is a problem with the iacv which i thought was weird. i would have thought that if engine speed dropped that would prove it was ok. that would suck if the fsm has typos. i could be reading it wrong but its pretty clear
again both the high idle and the not starting are not constant so diagnosis is tough

LvR

Ah - OK that sorta starts to make sense now.

However - the air cut valve can only, independently, limit the absolute maximum flow the IACV can allow into the engine - so if the air cut valve is funky (valve not closing when hot), its effect on the idle speed can only be zero (valve stuck fully open and IACV working fine) or alternatively if it stuck fully closed, not enough air can be fed to the engine when cold causing a low engine idle speed or even inability to idle controllably at all.

Like you, I have to conclude the FSM is wrong in its assertion that the IACV is faulty when the revs drop if you pinch/block the hose - the hose is after-all the only thing effectively feeding air to the motor ................ this is the way logic would dictate the ECU to be in control of the engine via measuring the air flow with the MAF.

sublunary

iTrader: (2)

yeah we are thinking along the same lines. i was really hoping that my iacv would not check out so i can get this fixed but i am running out of things to check. can you explain though why the car wouln't start when i blocked that hose? i got excited when that happened because i thought that was the root of my problem but air doesn't have to travel through the iacv to get to the cylinders so why won't it start up?

sublunary

iTrader: (2)

i put the iacv back on and the car started fine except i needed to adjust the idle. a little while later it wouldn't start so i pulled the #6 coil and plug and cranked to make sure it was getting spark and it was even though the plug was pretty oily. so spark is not and issue i don't think and niether is the iacv so now i am stumped

Greeny

iTrader: (43)

The next time it wont start,try a WOT start..this method turns off the injector pulse and opens your tb butterfly..

In a way you will eliminate,a possible rich start condition(i.e flooding out) and a possible air flow issue(iacv)

sublunary

iTrader: (2)

how is that done? do i get someone to crank the engine while i hold the throttle open manually?

Greeny

iTrader: (43)

No,you just put the accelerator pedal all the way to the floor while cranking.

sublunary

iTrader: (2)

ohi probably do that every time it won't start. you know, like a little aggression with my foot is going to persuade it to start. kind of like a person talking louder to someone that doesn't speak the language like that will make them understand

LvR

ME? - given all of your experiments here and the intermittent nature of the problem, I would devise a method to bypass the effect of the operation of the IACV completely.

Now I cannot figure from the FSM if there is some feedback mechanism located in the IACV stepper motor - if there is its going to be difficult, but if there is no feedback signal to the ECU then it could be fairly easy.

I would get the motor up to temp the next time it would start and get it to idle properly with the IACV in operation - once there, and stable, I would pull the IACV's plug and see if the idle stays fairly ok and constant. If idle stays fairly ok and engine continues to run, switch off and attempt to start again - if it starts fine, then you now have a method to finger the IACV/ECU.

With the engine idling and the IACV disconnected, adjust the idle speed via the bleed screw to get to about 2000+ rpm (idea being that when the motor is cold , that setting will allow enough air to enter the motor while the IACV is left decommissioned)

Switch off motor, go keep the girlfriend/wife happy for the night and in the morning see if the Max is happy to start (even though it may be a wonky idle or require use of the throttle) .................... if it is attempting to accommodate you theory and set the cold idle speed and count the number of turns on the bleed screw to achieve manual cold idle speed.

Repeat hot/cold engine cycle, but the next cold start ensure you have pre-set the idle bleed to the correct number of extra turns before you start - if it fires and attempt to idle, repeat for a few days (to get over the intermittent nature of the original problem) ........................Did you adjust the idle speed by allowing the ECU to realize you did this? (method with screw on ECU etc) ........................ was the IACV really dirty and can you see that causing a change in idle requirement setting of the bleed/bypass screw?

Are you quite sure as to the quality of connections on the TPS plugs and its operation?

sublunary

iTrader: (2)

i got to go to work so just quickly: i had to adjust idle because i took the idle screw out completely when cleaning it. i set the idle with the iacv harness disconnected per the fsm and no the iacv wasn't very dirty because i cleaned it a couple years ago. i checked the tps out very carefully too as well as almost every other sensor i could think of. i have an o2 sensor coming in the mail and front three coils. i am going to replace fuel filter too just to be sure since its cheap. some of the spark plugs are pretty oily and the compression is down on some of the cylinders so i wonder how much that might contribute to it. ill comment on the first part of your post after work when i have time to think it through. thanks for the help/input

sublunary

iTrader: (2)

you?
i doubt there is feedback to ecu because there are only two wires going to the iacv-aac valve. so that means the ecu is just sending voltage to valve, right?
i don't believe the ecu controls the iacv at idle. that is controlled mechanically by the idle screw and the wax/piston reacting to the coolant temp.
i believe(correct me if i'm wrong) the ecu only triggers the iacv-aac valve when the ecu detects load from the power steering oil pressure switch. that increases air flow to compensate. the iacv-ficd solenoid gets ecu input when a/c goes on. and actually now that i look at it, that may not even go through the ecu. there is only ecu harness terminal #4 that goes to the iacv-aac and no listing for the ficd solenoid so that may come direct from the a/c unit.

i don't think that you can set the idle that high with idle screw all the way out but i understand where your going with that

im not sure i follow you on this part, except the part about the wife being happy. unfortunately what really will make her happy is getting the car running so she doesn't have to take the subway to work

CapedCadaver

iTrader: (8)

it controls it at idle if the idle screw is set too low. Well, at least mine does. I can tighten the screw all the way down and my idle doesn't change. the iacv responds to a multitude of signals, including, but definitely not limited to.. gear range switch (a/t), PS pressure switch, ECTS, TPS, a/c, CAS, etc

LvR

Indeed - thats why you have a idle speed setting procedure involving the ECU's little rotating switch - during the idle speed setting procedure, the IACV is told not to get involved by the ECU - once you have manually set the desired speed, you allow the ECU to monitor and keep revs constant, and via the IACV, allow more air should the revs either drop for some unknown reason, or is anticipated to drop because of known loadNot surprised you don't follow - I cocked it all up with bad grammar and spelling.

The idea is basically this:

You, with your little screwdriver in hand and your ability to adjust the IACV's bypass/bleed and with the IACV disconnected, must make the Max's air system react like a carb fed engine with cold idle control - you being that control. If you can do that successfully and repeatedly while experiencing "good" and reliable starts, then you can prove that the IACV/ECU is somehow involved in your intermittent miseries

CapedCadaver

iTrader: (8)

except mine doesn't work right. I turn IACV off... set idle... turn iacv back on, it goes up by 200rpm. I can close the valve down and idle rpm stays steady at 900 warm. Sometimes higher if it feels like being higher. I have to use a very heavy foot on the brake pedal when in gear to keep the car still sometimes. No wonder my braking sucks, the IACV is trying to keep the car moving. I usually downshift to 2nd when slowing down under 35mph, to help the car slow down.

LvR

Guess you have work to do then don't you? ................ alternatively just set it 200rpm lower to start with till you solve the mystery higher idle.

Is your motor properly warmed when you set idle speed?

Is that air cut valve closing when hot (go through a few hot/cold tests to see it being a reliable mover)

ECT ok?

What is your cold engine idle speed while in neutral/park?

CapedCadaver

iTrader: (8)

1500 cold 10 sec after start in N/P

if i FULLY shut the idle screw, warm idle is still 900. I either have a bad iacv, bad aircut, bad ECTS, or an intake leak.

i'm thinkin' i can test the ECTS in a pot of water w/ 3rd party thermometer and multimeter... right?

i usually let the rad fans cycle on then off before attempting to set idle.

also i INTENSIVELY cleaned the iacv last month. I took it apart into all 3 pieces, sprayed TB cleaner over the valve, seat, air cut, air cut spring, all air passages.. everything. Took a q-tip to the valve seat...to rub any buildup off...Still didn't help.

sublunary

iTrader: (2)

ok i understand. thats why the fsm says to unplug iacv valve when setting the idle. and lvr, i might have to do your method for a few weeks to have confidence that the iacv is at fault because the car might drive fine for a week or two and then with no warning refuse to start. but what would be valuable is if i could try this when it doesn't want to start. if i could let out the idle screw and unplug the iacv harness and the car starts that would be more definitive. im i right or am i missing something? after all i am a little distracted by the redsox world series game on right now(with apologies to those outside of the states that might scoff at the "world" part)
thanks for your responses guys its very helpful
luke

LvR

Hmmmmmmmmmmm..............

Cold, first start idle seems fine

To make any internal combustion engine run smooth, it needs a specific air fuel ratio to ensure reliable ignition. The ECU knows all about the volume of air entering the engine via the MAF, and ensures that the correct amount of fuel is added by also looking at temperature of the motor, and then varying the exact moment that ignition is initiated.

IMO an uncontrolled SMOOTH high idle is the result of the ECU definitely knowing about the air/fuel requirements at that moment - while an intake leak would make more air enter the motor, the ECU wouldn't know about that (it has not passed via the MAF) and I m pretty sure you will not have a SMOOTH idle as the motor would be running lean. The only other place where unwanted but metered air can enter the motor is via the throttle body (if the throttle butterfly is not seated on its proper rest position for whatever reason or if there is something wrong with its shape)

I would start investigating there .................... with a blocked off IACV assembly, and will be looking for the motor to run when hot, but possibly at only around 500rpm, if the throttle assembly is properly adjusted/located ................................. after having confirmed the correct operation of the TPS first.

LvR

Luke

The fact that you have earlier determined that spark is not the issue would point to something in the fuel system .................... and while the IACV may play a role I suspect that there is something way more fundamental happening at those times when the motor refuse to start.

I would again systematically go through each and every plug/socket/connector/sensor involved with the motor and mechanically clean it and reassemble.

I would get a fuel pressure meter (or a cheap oil pressure guage that is functionally the same except for the silk-screened dial) and plumb it into the fuel line after the filter in order to monitor fuel pressure while behind the wheel, and start there believing its the most obvious and most likely cause of the issue.

IACV assembly I would probably spend time on only if all else fails

sublunary

iTrader: (2)

i agree that it seems like something more fundamental, as you put it. when it first happened i was wishing i had an in-line fuel pressure gauge actually. i was hoping i could just put it in right after the filter and leave it in but i would only be able to see it from under the hood rather than in the car. how would you go about putting it inside the cabin? i guess there are kits that have a pressure gauge that you can run wires from, through the fire wall and hook up a gauge from the inside? i don't really have a desire to have a gauge permanently mounted like turbo'd cars do... the simplest thing to do seems like just leaving one hooked up under the hood but i wonder if there are reasons not to like heat or vibrations that could cause a hazardous leak or something.
as far as the iacv, it seems to be fine other than a cracked hose that i need to replace so i am moving on from that for now.

sublunary

iTrader: (2)

i know some people have had an unsteady idle because of gunked up tb causing the butterfly valve to not seat properly. a quick spray of cleaner and a paper towel gave them a solid idle again

CapedCadaver

iTrader: (8)

once i cleaned the TB with some cleaner and a toothbrush/paper towel. at the same time i cleaned the iacv and it made no noticeable difference. That was back in like, february the first time.

LvR

I have a brass T-piece on standby ............ its got 2 push-on 7mm nipples for rubber hoses between the filter and rails, and a 3rd nipple to accept a 3mm Teflon tube with a ferrule mount - tube is the type that the cheaper mechanical oil pressure guages comes with (oil/fuel/heat etc resistant) - when the need arise I just drop that block into the fuel line and route the Teflon tube out under the bonnet, through the door seal and drop the pressure meter on the passenger floor to look at only when the problem situation arise (I don't need/want those things mounted either).

When it served its purpose it takes seconds to restore the original fuel hose to its position and hang the meter in the garage (hopefully to never be used again)

sublunary

iTrader: (2)

is there any reason i shouldn't permanently keep a gauge in-line? i think it would be nice to pop the hood at any time and be able to see the fuel pressure. there is certainly plenty of room there...