New member of my toyota family and idle question

[St Runner]

I bought another Tacoma and am selling my old tacoma. Its a 02 3.4 5 speed extra cab with a rear locker. 135k miles. Swapped everything i wanted off of my 99 single cab and am going through the maintenance. The problem I have is the high idle of 1200 rpm. I know its a tacoma and not a 4runner but I thought I would ask here first before I signed up for a tacoma site and got my a** handed to me. Starts up a around 900 rpm when cold and increases in speed until she is fully warm at 1200. Rock steady at that idle as long as she is warm. I removed the throttle body and cleaned it as well as the IAC and reset the ecu by disconnecting the battery. All is good and tight with the cables and throttle plate. I am thinking the IAC is bad and I have also read that there is a temperature sensor too. No codes and runs perfectly. Any suggestions for me? I have never had an idle problem with any of my other toyotas so I don't have a lot of experience with this one. Some pics of the family too

 

[thegipper]

I would check for vacuum leaks. If you don't find any, I would replace the IAC.

When I swapped engines, I had the exact same problem. High idle that wouldn't go away. I ended up swapping throttle bodies from my old engine and reset the computer. It takes a few days to "level" out but it completely fixed the problem.

I assumed the IAC in my donor motor was the culprit.

 

[St Runner]

Thanks. I checked for vacuum leaks and all the hoses are in surprisingly good shape. I also think it is the IAC sensor part as it is too consistent and doing just the opposite of what it is supposed to do. All my other toyota's start around 1200 when cold and drop down to 750 when warm. I drove it around for a full day with multiple starts and stops after I reset the ecu and it did not change at all

 

[Buckaroo]

Just guessing really but there are at least two things that cause idle to increase in normal operation - power steering pump and ac compressor. You might try to unplug one at a time and see if the idle drops.

Buckaroo

 

[St Runner]

Thanks for the suggestion. Turning the ac on and off does not change the idle speed at all. When I have some time, I will see if I can disconnect that source. On both my 4runners turning on the ac bumps the rpm just a little. Nothing changes the idle on the tacoma except for temperature and it is doing the opposite of what it is supposed too. Going to order a new IAC valve today and see what happens. I have one off my parts 4runner but I don't know how well it works or if it is the same for the tacoma

 

[DaMonkey]

...I have also read that there is a temperature sensor too. ..

Yes. At least on my 4runner, has intake air temperature sensor (IAT). Will affect the mixture and in turn affect idle.

Do you have an OBD2 reader? I think air intake temperature may be one of the basic readouts and you can see if it's working? When it's cold, should read the same as ambient, and it should warm up with the engine.

IAT sometimes built into MAF. If your MAF has 5 wires, IAT prob built in there. But, this is worth checking out based on behavior you are describing. Also clean the MAF always good idea.

 

[St Runner]

Thanks, thats good information. Yes there are 5 wires on the MAF. Looks like i need to get a toyota service manual and start figuring this all out. Interesting that when I cleaned the MAF all 4 screws were loose. MAF was pretty clean and did not seem to make much difference after I cleaned it. I will throw an OBD2 later today

 

[Buckaroo]

Thanks for the suggestion. Turning the ac on and off does not change the idle speed at all. When I have some time, I will see if I can disconnect that source. On both my 4runners turning on the ac bumps the rpm just a little. Nothing changes the idle on the tacoma except for temperature and it is doing the opposite of what it is supposed too. Going to order a new IAC valve today and see what happens. I have one off my parts 4runner but I don't know how well it works or if it is the same for the tacoma

Of course, if it was already sending a signal to increase the RPM (due to faulty pressure sensor), it would not do so further when you turned on the ac. But, the FSM does say the increase should be to 850rpm and you are at 1200rpm so that is inconsistent....

Buckaroo