cold idle issue

S

stackz

New member
ok. 97 4runner 3.4 engine automatic.

replaced a cracked head and got it back together. it would always idle @ 1500rpm. cold, hot, whatever, it was 1500rpm. with the cold crank up you could distinctly hear the "cold idle woosh" noise these things have. once it warmed up some the woosh would go away. but always 1500rpm.

I pulled the IACV and noticed the valve was stuck around 40% open. cleaned it out so that it has good action. put it back on and now it would idle @ 750rpm hot...yay. waited a night and cranked it up cold and it wouldn't stay running. it would crank up and fall off and die unless I manually held the throttle a couple of seconds and even cold it would settle to 750rpm and I no longer heard the woosh noise.

I went to the u-pull yard and grabbed the only IACV they had from a 95 3.4 Tacoma (I know, different part number but I just wanted it to test). it had good action so I tossed it on and now the car always idled at 2000rpm but the cold temp woosh noise was back until it finished its cold idle warm up and then it would go away.

I ohm'd the original IACV and cold ohms it was 21 on both sides. I also did the 12v battery test and it opened and closed the correct ways. I'm going outside in a minute to check the hot ohms on the IACV but what do you guys think?

I ohm'd the ECT sensor and it ohm'd correct. I also read the ECT in realtime using my Bluetooth obd scanner and it did go up in temp.

could it be the valve even though the ohm and 12v test are correct?
 
Register to hide this ad
It can definitely be bad and pass an ohm test and have power.
Reason being is it doesn't work by changing resistance but by having the resistance of its grounds changed (controlled by the ECM) which determines IAC position.

So here is how you would test it and be gosh darn sure you've nailed it.


1. Monitor the voltage at the Idle Air Control (IAC) valve:

A. The White/Blue (W/L) wire should be 12 volts.
B. The Brown/Red (BR/R) wire should read 6-7.5 volts.
C. the Black/Red (B/R) wire should be 8-9 volts.

2. Ground the BR/R wire and the RPM should increase. If grounding the wire does not change the idle speed, check for a sticking IAC motor.

3. Ground the B/R wire and the RPM should decrease and the engine should stall. If grounding the wire does not change the idle speed, check for a sticking IAC motor.

4. If there is voltage on the W/L wire and no voltage one of the other wires, look for open windings in the IAC motor.

 
perfect. I didn't see this test in the FSM I have.

will do this tomorrow. I guess the hardest part will be getting up in there while the engine is running since the IAC is under the intake tube.

will likely get a couple paper clips from work and stick them in the leads and hook some alligator clips to them so I can check voltage and ground the wires.
 
Good to know. Is a 1500 RPM idle too high? In my '97 3.4L automatic, the idle stays around 1500 in P, then drops below 1000 in D. Were you referring to your 'high' 1500 idle in P or D?
 
EatonKyleH said:
It can definitely be bad and pass an ohm test and have power.
Reason being is it doesn't work by changing resistance but by having the resistance of its grounds changed (controlled by the ECM) which determines IAC position.

So here is how you would test it and be gosh darn sure you've nailed it.


1. Monitor the voltage at the Idle Air Control (IAC) valve:

A. The White/Blue (W/L) wire should be 12 volts.
B. The Brown/Red (BR/R) wire should read 6-7.5 volts.
C. the Black/Red (B/R) wire should be 8-9 volts.

2. Ground the BR/R wire and the RPM should increase. If grounding the wire does not change the idle speed, check for a sticking IAC motor.

3. Ground the B/R wire and the RPM should decrease and the engine should stall. If grounding the wire does not change the idle speed, check for a sticking IAC motor.

4. If there is voltage on the W/L wire and no voltage one of the other wires, look for open windings in the IAC motor.

Click to expand...

just something I was thinking about last night...

when I run my volt test on each wire, red lead goes into the wire I'm testing and the black lead goes to body or battery ground right? that wont "ground" each wire at the same time due to the multimeter taking a reading right?
 
stackz said:
just something I was thinking about last night...

when I run my volt test on each wire, red lead goes into the wire I'm testing and the black lead goes to body or battery ground right? that wont "ground" each wire at the same time due to the multimeter taking a reading right?
Click to expand...

Ya that's how you would test voltage. No the wires your testing will not be grounded through the meter because the meter has a very high internal resistance. You'll have to ground each one by back probing the connector with a paper clip or similar suitable bit and clipping a wire to it then touching the other end to ground as to give it a direct nonresistant path to ground.
 
thats what I thought but wanted to make sure. I use the el cheapo harbor freight red multimeters and these things have done some funky things in the past.

and I am by no means an electrical engineer lol
 
EatonKyleH said:
Click to expand...

so where did you pull this diagram from and is it what you used to give me the voltages? if so you gotta tell me how to read this properly lol.

regardless, did the tests as instructed and I'm getting the proper voltages on each wire. when I grounded the brown/red and the /black/red wires (independently, I checked each wire on its own) all I got was a spark from the grounding point and no idle up or down respectively. tells me the motor is stuck/fubar.

this isn't my car so I don't feel like screwing around with the motor in the valve at all, just let them pay me back for the valve. just going to buy a new valve and toss it on and be done with it so the car doesn't come back to me in a month.

funny that in the test section of the FSM for the IACV it doesn't give the voltage check/ground info...just the ohm stuff causing me to scratch my head this whole time lol
 
stackz said:
so where did you pull this diagram from and is it what you used to give me the voltages? if so you gotta tell me how to read this properly lol.

regardless, did the tests as instructed and I'm getting the proper voltages on each wire. when I grounded the brown/red and the /black/red wires (independently, I checked each wire on its own) all I got was a spark from the grounding point and no idle up or down respectively. tells me the motor is stuck/fubar.

this isn't my car so I don't feel like screwing around with the motor in the valve at all, just let them pay me back for the valve. just going to buy a new valve and toss it on and be done with it so the car doesn't come back to me in a month.

funny that in the test section of the FSM for the IACV it doesn't give the voltage check/ground info...just the ohm stuff causing me to scratch my head this whole time lol
Click to expand...

Haha well there ya go! Glad it was on point for you.
The diagram is from factory service information.. I looked up your vehicle at work. Any particular questions about reading it? I'm not sure exactly what you'd like explained....

That test was written by another technician. Most of the tests I provide people with on here were written by another tech or myself. The voltages provided in the test were recorded when testing a known good valve after replacement so you know what is normal and abnormal. In the field this kind of data and testing is a lot more helpful because of the detail.

again, Glad it helped.
 
and the saga is finally over and I can give the truck back. joy has come to me.

kinda funny though, toyota dealer wanted $190 for the valve with a 1 yr warranty. the valve was $220 after taxes at autozone...but was a toyota valve and had lifetime warranty, and came with the gasket too.

tossed it on and cranked up the truck and it idles like it should!

that voltage procedure really should be tossed in one of the tech stickies so it doesnt get lost on here considering its not in the FSM though.
 
You must log in or register to reply here.

Members online

Total: 314 (members: 3, guests: 311)

Forum statistics

Threads
278,305
Messages
3,554,041
Members
248,016
Latest member
Advally Service

Share this page

Trending content

Back
Top