Idle Air Control valve question

[TXRick]

I've been messing with this high idle problem for years...
I did all the required reading and cleaning but since I've been DDing it these last few weeks, I decided to give it another go.

I bench tested it and the metal flap opens and closes like it should. I took the motor(?) off and cleaned it too. Still bench works.

If I unplug the IAC it idles perfect but CEL. I know replacing it would solve my problem but $$ problems.

When I took the motor off, should the flap be open or closed? I reinstalled it closed.

Any other advice?

 

[TXRick]

I just opened it up again and it doesn't matter...there's no way to install the little motor with the flap open. It defaults to closed. So, when I turn my runner on, the IAC makes the flap open, so high idle. When I unplug it, flap closed, better idle and ok driving characteristics.

What tells it to be open or closed? Could there be another part that doesn't throw a code telling my IAC to stay open all the time? Is the IAC just broke even though it benches good?

 

[jgue467]

What CEL do you get? I would suppose the open/close function is ECU controlled?

 

[TXRick]

Not sure yet. Just unplugged IAC so I'm sure it has something to do with that. I'll head to autozone and see. Could be ECU, but I think I read the engine temperature control sensor might have something to do with it.

 

[TXRick]

Throwing code P0505. No surprise since the IAC is unplugged...going to plug it back in and unplug the temp control sensor and see what happens.

 

[TXRick]

Unplugged the temp sensor and it had a hard time starting but does idle perfect at 700rpm...letting it sit now to clear the code. We will see if it throws another.

 

[sawguy]

I have the exact same problem. From what I've read, if the P0505 resets after the IAC is unplugged, you either have a wire open between the IAC and the ECU, or the ECU is bad. Just been too cold lately to try and test the wires. Thinking of just buying a used ECU and hope that takes care of it.

 

[TXRick]

Hmmm...I'll get on that next.

After unplugging the ECT, I get a po115(ECT sensor circuit malfunction) and no po505.

What you are saying makes unfortunate sense. With everything plugged in, no CEL and high idle. With the IAC unplugged, better but not great idle and with the ECT unplugged, perfect idle but both throw a CEL. I'm thinking that there's nothing wrong with either sensor but rather some kind of other communication problem...like the ECU

 

[GeoffCO]

Rick, where is the coolant temp senser? I've heard there are 2. (i don't know where is the one you are talking about)
I am having a similar issue, high idle. So I'm taking the much info I can before I open the hood. Thx!

 

[TXRick]

Rick, where is the coolant temp senser? I've heard there are 2. (i don't know where is the one you are talking about)
I am having a similar issue, high idle. So I'm taking the much info I can before I open the hood. Thx!

Yeah, there are two. The one on the firewall side is a pain to get to and only talks to your gauge. The one up front is easy. There are two groups of wires behind the 3400 cover. The one with two wires goes to your knock sensors and the one with three wires goes to your engine temperature circuit sensor which talks to the ECU. It will take a little digging but looks easy to get to with sockets and stuff. I read you need a 19mm to change it. I'll get a pick or find a link here in a minute.

 

[TXRick]

Rick, where is the coolant temp senser? I've heard there are 2. (i don't know where is the one you are talking about)
I am having a similar issue, high idle. So I'm taking the much info I can before I open the hood. Thx!

http://www.toyota-4runner.org/attachments/3rd-gen-t4rs/32174d1282787997-water-temp-gauge-comp.pdf

 

[GeoffCO]

http://www.toyota-4runner.org/attachments/3rd-gen-t4rs/32174d1282787997-water-temp-gauge-comp.pdf

Rick thank you so much for that!!

 

[TXRick]

Yeah, no prob. If you just want to test it, the connector is easy to get to. Just feel around behind the 3400 cover and unplugged it.

 

[GeoffCO]

Yeah, no prob. If you just want to test it, the connector is easy to get to. Just feel around behind the 3400 cover and unplugged it.

Do you test it when cold and then when hot?

 

[TXRick]

Do you test it when cold and then when hot?

Yup, the hard start takes about 4 tries. Sounds exactly like its starving for air. Every time I go to the store or whatever, I come back and it starts right up first time and sounds strong.

So far this week, the gas gauge is dropping very slowly. Only been 80 miles so far. Was getting 12 mpg before. Drives good and starts right up as long as it's warm.

 

[TXRick]

So, I've got an 01 and I'm going to swap ETCs. Had to write it down before I forgot I'll get to it in the morning.

 

[TXRick]

So, I've got an 01 and I'm going to swap ETCs. Had to write it down before I forgot I'll get to it in the morning.

Yeah...I forgot to do that...don't even remember posting...but....

FIXED

So, after unplugging everything and blah blah blah all my check engine lights went off but still high idle. I was driving around one day and noticed my idle was fine. Whoo hoo! It fixed itself!!! Wrong. Wrong. After about 15 mins my check engine light came on and the high idle was back. I went to the nearest parts store and she popped a p0505! Idle Air Control Valve fault. After driving it a few days the CEL went away and high idle was back. Still not convinced I ordered the cheap eBay IAC for about $50 vs $200+ for others. Installed and working perfectly! 700 on the dot and about 850 with the AC on.

I figure the IAC was broke the whole time but wasn't telling the ECU. That lying sun of a...

So if you ever get a 1500 constant high idle with no CEL...change your IAC.

 

[TXRick]

Update: After two tanks of gas I have a moderate MPG increase (14.1 and 15.2). The CEL came on again today and it popped ECT fault. No real idle change. I replaced that and all is well for now.