Please help me someone, low/stumbling idles - goin crazy here...

[redincali]

ok so for the past 6 months or longer i have been trying to fix a problem with my car. The problem is that when i start it, warm or cold, the rpms jump up like normal but then it dies or catches itself right before it dies at 0 rpm. What i have to do is feather the gas pedal til it stays at a constant rpm, usually 500 then it rises.

I have been looking for solutions online since it started and still haven't found one. I replaced the fuel filter, regulator, dampner, & pump. I've checked all vac lines, sprayed to look for leaks, still found nothing. I ran diagnostics on the ECU, it said my knock sensor and coolant temp sensor are out. I replaced the sensor, reset the ecu, drove for a day or two and checked it again. no errors found.

finally one day about a month ago i was reading about the IACV/AAC valve and it seemed like other people had my problem and that was causing it. well i just finished putting in a new AAC (30 mins ago) and now the idle is even worse. its 90+ degrees outside so my car isn't cold from weather. i even checked the old AAC when it was out by connecting power and it actually seems to be fine still.

So at this point im out of ideas. I dont want to sell my car and i dont have the money to just take it to a shop. So if anyone has anything to help me, please let me know cuz this sucks and i would appreciate it a lot. thanks.

[Zwicked]

Did you use a new gasket for the IACV unit after it was off?Also did you set the base idle properly as that needs to be done if the AAC was changed or it won't idle properly.

you need to:

- warm the engine up to operating temp- unplug the AAC and start the engine- turn the screw on the side of the IACV until your tach reads 650- plug the AAC back in while it's running. The idle should immediately rise, and then settle to about 750

If the idle is still bad after that, I would pull the injector connectors and see if they are all corrosion free, and test the injectors with a multimeter to make sure none are bad. They should read 10 to 14 ohms to be in spec.

If you find corrosion on the connectors, pull the MAF, PTU, and CAS ones and make sure they are clean as well.

Also, if all of the above are done and it's still the same I'd test the PTU

[redincali]

Yes, i replaced the gasket when I changed it. I read that is a must so i didn't attempt until i had one. Also, i did set the idle properly but when i plug it back in, there is no change. The plug looks like it might have some bad corrosion so im going to replace it now. I didn't know it was that bad until I removed the unit this morning. Where could i find that? and what is the PTU?

[Zwicked]

If that connector is in bad shape, pull the one off the coolant temp sensor and check it as well. It's on the top water pipe on the front of the engine, the connector with the spring clip like the AAC unit.

If the AAC one was corroded, likely all of them are. The most important ones in your case are likely the CAS, PTU, MAF, TPS and Coolant Temp Sensor as all of those tell the ECU certain conditions of the engine and without that communication it won't run properly.

I would start by pulling those connectors and see what they look like

Here is a bit of a guide where the parts are

http://www.z32photoguide.com/

[redincali]

Thanks for the link. I just looked up to see what the PTU was. My connection is clean and I do have the new one from the recall, so i dont need to change it either. I changed my coolant temp sensor before and cleaned its plug at the time. From what i remember, it wasn't very bad.

I have already checked the maf plug before hoping it may have been the problem. So from what you tell me, the other ones i need to check are my cas and tps. Ill be doing that here in a minute. thanks

edit: actually i have checked the crank angle sensor before and its perfectly clean. CAS, duh, didn't register in my mind til i looked it up
Modified by redincali at 5:51 PM 7/3/2009

[redincali]

ok so i just checked the other connections on the PTU and cleaned them, and cleaned the TPS connection, it was corroded a lil bit. but i noticed the plug that connects onto the TPS has 3 hols in it but only 2 have wire connections. is that normal?

[redincali]

Well, I have a new plug coming for aac valve. So ill replace that as it comes in. But since i cleaned some of the corrosion off the other plugs, its been running a lot better on the start up. thanks again. I hope the new plug finishes solving the problem.

[evildky]

did you adjust the iacv?

[redincali]

did you adjust the iacv?

just the idle, i adjusted. is there another part i need to adjust on it as well?

[redincali]

edit:...im not good with electriciy, so i have my pops helping me. we tried tracing the line using a toner. we followed it to a plug near the main fuse box by the headlight and also a plug on the right side of the engine, under the plenum. we were tracing it because there is no power to the plug itself or even the wires.

we cut the plug off since its going to be replaced and traced from the wires. the toner shows continuity(?) as well and when hooked to both wires, it shows continuity. but on plug thats on the side of engine is fine. only one side has power and other is ground.

my question is, does this stay on all the time anyways? so i would be able to hot wire it. or does it need to be on and off at certain times in which maybe i could do a toggle switch? i really dont want to go that way but if all else fails.

we did test the engine running with power directly to the aac valve and it significantly raises my rpms from where they are. im reading through the online service manual to figure it out but if you have any more help, it would be appreciated.

Modified by redincali at 10:21 PM 7/7/2009
Modified by redincali at 10:27 PM 7/7/2009

[redincali]

bump...

[ztommyx]

what's the update?

did you check for loose and/or crack vac hose?

[redincali]

ya i have checked all the hoses. but as of right now im stuck with the electrical part. i dont know what else this ties into. its not getting power so the other clips that feed off it may not be as well.from what my pops tell me, the 2 wires in the yellow clip are getting continuity(?) which means they're touching somewhere.

ive looked on the online service manual and found that its on the EFI Harness but theres no depth on the picture so its hard to tell where it may be leading too and it doesn't stay which wires in the efi are tied together.

[ztommyx]

now, whats going on again? i'm lost in all your posting...

a single wire couldn't have caused irratic idle, if thats what you're trying to figure out.

[redincali]

ok, no. the problem is my aac valve not working. i thought it may have been the unit itself but it was fine. its just not getting power from the yellow plug. and im assuming the white one as well. from what i have read, the hexagon piece with the white plug is for when the engine has a load (a/c, ps, etc.). it should always have power to the yellow right? because in order to set the idle, you remove it then reconnect it and it changes your idle, so its regaining power.

i put a new yellow clip on. but with the clip off and the wires stripped, we tested them. we found that there is continuity between the two somewhere. which means they are connected somewhere, like one line. but using a toner, we can trace the line. it led to another clip on the middle right side of engine, right under plenum, and it also led to a clip near the relays by the driver side headlight. there shouldn't be continuity, one should be power and the other ground. i located it on the online service manual and its on the EFI Harness

[redincali]

ok well if someone could just answer me this, it would be great..... can i hot wire the aac to be on whenever the car is or is it ecu controlled?

[valkyie]

Maybe I am wrong but I thought the AAC was controlled my the button on the pod for turning on your AC which raised the idle of the engine. Are you trying to get this to stay on all the time?

[labcoatmonkey]

Ive been havin the same problem with my idle... is it steady when the car is cold? Also does it run rich once its warm? Its been buggin me too I replaced the idle valve and nothing has changed. Are you sure its an electical problem? Try hookin it up to a computer it might tell you that there is a bad connection to the aicv/acc valve.

[redincali]

From what i have learned, the AAC has 2 parts to it. One is for your idle, the other is for when a load is put on your engine (a/c, p/s, etc.).

To set your idle.... unplug the yellow connector, warms your engine up to mnormal, set your idle to 600-650 using screw, reconnect the yellow plug and your rpms jump up to 700-750.

Thats how i have read to set the idle, many times. So this is my thought.... the engine is warm when u set the idle on the AAC. when you unplug the yellow clip, you lose 50-100pms until its reconnected right? so that would mean ther is a continuous supply of power going through that plug. even tho the car is warmed up. So does that mean i can just wire it to have power all the time?

but even with that, the other part of the AAC that kicks in when there is a load on the engine may not be working. And i dont think it is working because when a load is on my engine and the clutch is in, my engine likes to try and die on me.

the cold start is controlled by an air regulator that is connected to the AAC with a hose. it goes from the regulator to the AAC to the engine. the regulator is essentially a coil like a thermostat that opens/closes depending on the warmness of your vehicle.

like i stated up there, you set your car's idle when it is warm. and at that time, there should be power going to the AAC so the only time it shouldn't have power is when its cold, which may not be true either.

[redincali]

heres a short vid i made a lil bit ago

http://www.youtube.com/watch?v=6jMRSUynvFs

it doesnt show what happens most of the time but it gives u an idea (hopefully)

[Cyman]

I don't have time to read/follow the entire post.. but that seems to be almost the exact same thing my car would do when it had bad injectors.. my car wouldn't usually die when I started it, but the idle would be very low.. and sometimes I would have to keep my foot on the gas for a bit. coming to a stop sign/light it would drop to almost zero rpm then rebound, and I couldn't get the idle to stay at a consistant spot even when the engine was warm.. sometimes it would idle right around 700, sometimes around 450.not sure if you've tested the injectors, but if you haven't I would say give it a shot. GL finding the problem if this isn't it!

[redincali]

my injectors are fine. i just need to know about the AAC's power. thats it really. i've narrowed the problem down to it but the problem is in its plug coming off the harness. thats where i need help. because there is continuity between the two wires in the yellow clip. i have connected power directly to the AAC valve with the car warmed and running and it raises like its suppose to as if you connected it at the end of setting the idle propertly. but other than me giving it power myself, it doesn't work.

[labcoatmonkey]

when u unplug the aac, does the engine still have an erratic idle (goin from say 1500 rpm down to almost zero and rebound)?

[redincali]

when u unplug the aac, does the engine still have an erratic idle (goin from say 1500 rpm down to almost zero and rebound)?

plugged, unplugged. right now it doesn't make a difference to my idle because its not getting power. i've had it disconnected for about a week now and its been the exact same as it was the weeks before when it was pluggin it. its just not getting power but im not sure where the wires run to and what else is on the same line because it may not be getting power as well

[redincali]

the idle isn't erratic when my car sits there, except for the start up. but then until its warmed up, it will drop down and almost die as i hold in the clutch while driving. siting there and pushing the clutch changes nothing.

no one knows if this is suppose to have power all the time? what it feeds off of or what feeds off it? thats where im lost.

[emt2898]

the things i have found in the manual say that- "the a.a.c. valve operates according to signal sent from the e.c.u. the c.a.s. determines engine speed and sends a signal to the e.c.u. the e.c.u. then controls the on /off time of the a.a.c. so that the engine speeds coincide with those memorized in the ROM."

diagnostic procedure 41, section EF & EC 156 & 157 in the manual describes the a.a.c.

not sure if these are any help or not, you might have already been through these i dont know, its just what i found. it sounds like you are getting nothing to the aac from the ecu. from what the book seems to say you should be getting an ign signal from the ecu to your aac. maybe a short between the two wires? does your car idle up like its supposed to when you turn the air on? sounds like you may have to chase down a short though in your egi harness.... i just replaced mine and kept my old one. if you still need to know where all it runs i may be able to help you out when i get off work wed morn. maybe something will help.

[redincali]

awesome, thats some useful info. thats what i was wondering, if the aac was ecu controlled or not. i found a diagram earlier and it shows where each wire leads. i was thinking of just making a new line for the aac directly. would that work? does it run to the ecu or one of the clips near the headlight?

[redincali]

while im thinking about it, how hard was it to replace that harness? maybe thats what i should do. i tried tracing it using a toner and it let to a white plug that went on the driver side of engine, next to the wheel well.

[Zwicked]

Have you ever checked your Coolant Temp Sensor or it's connector?

You can't connect direct power to the AAC solenoid as the ECU constantly modulates it to control the idle under different conditions. Even when the AAC is completely dead, the car usually idles low and a little unstable but it doesn't stall. You can simply turn the base idle screw to raise the idle a bit until you fix the AAC issue, not that it will idle perfectly, but I think your issue is something else.

I would:

Test the PTUTest for good spark at all 6 plugsTest the MAFDo a compression testTest all the injectors with a multimeterMake sure all connectors are free of corrosion (CAS, PTU, Injectors, MAF, CTS, TPS, AAC, Air Regulator)Do an intake leak test to make sure there are no vacuum leaksTest fuel pressure

Confirming all sensors and components are in spec and operating etc usually leads to finding the issue and it doesn't take that long.

If all the components test out properly, then you can move on and test the harness from the ECU plug to the component plug for continuity rather than randomly changing the harness until it's known to be bad. The shotgun approach isn't usually successful, just expensive and frustrating.

All of the component measurement specs are in the manual EF&EC section starting about P 178 and P42 is a troubleshooting guide for problem characteristics that might be helpful

http://www.300zx-twinturbo.com/cgi-bin/manual.cgi


Modified by Zwicked at 10:23 AM 7/21/2009

[redincali]

I replaced the cooland temp. sensor like 6 months ago. its connector is clean. i have already checked and cleaned the CAS, PTU, MAF, TPS, AAC, Air Reg, Injectors, checked the vac lines, can a diagnostics on the ECU. Im not "shotgunning" this, i have been going through all kinds of possibilities, narrowing it down to come to this. ive gone from the fuel tank to the engine. new pump, filter, fuel damper, fuel regulator, spark plugs, and so on.

im thinking maybe an O2 sensor may be out, ill have to run the ecu again for codes. but still, there should not be continuity in the clips wires to the AAC. once i get that delt with, ill move on. but for now thats what im looking to fix.