Another p0505 quandry...

bought a 99 tacoma, 2.4l 2wd 2 years ago. had 203k miles and always had a high idle with NO codes. at 209k now...did usual tune up. recently got a p0505 code which will not reset. so far have replaced the IAC x2, TPS, coolant temp sensor, thermostat, and both o2 sensors and cleaned the throttle body. built a smoke machine to test for vac leaks. there are none. no difference when removing and plugging the brake booster vac line. no difference if unplugging iac. power to iac plug. pcv valve and egr good. air cleaner good. vsv ???
aside from replacing the throttle body...anything else i can check? this is frustrating as heck.
truck starts fine, idles 900rpms smoothly when cold with occasional surges, then climbs to 1150rpm when hot. drives well with no loss of power as far as i can tell. ready to take it to the shop...

 

...is the IAC getting enough juice?

Hope it is a simple fix!

 

will check that thanks.
any other ideas?
i understand from reading that this is a very common issue with potentially multiple causes.
thinking about sending throttle body to maxbore. heard good things. his price is around the same as buying a good used TB...

 

I wish I could tell you more... I never had to encounter this but after reading the #1 post about replacing the IAC twice. It is a mystery that the p0505 code won't reset... Possible poor alternating current?

As a general rule, the first thing is to do is; (I was taught that) to check if fuses are okay & power going through and if the all the grounds are solid... And if alternator diodes are good.

It could be that the throttle body is gummed badly or a foreign object/matter blocking the bore...

Let us know what happens next (before wallet gets lighter)!!

 

thanks again for reply. all fuses i have checked. will chase down the grounds for good contact. have you ever adjusted the throttle stop screw? the one that keeps the butterfly open a bit...i realize this may mask the problem and need to find the reason for the high idle. seems too much air is getting in...will also check voltage at iac connector.
cleaned throttle body . not too much gunk in there since i cleaned it originally when i got the truck.
alternator diodes huh? will search how to check. no issues with lights or any electrics it seems.
thanks again

 

To be truthful, I lost my last 2 Tacomas to frame rust before I can do any work on motor LoL I just did regular maintenance & it ran great. No need to mess w/idle screws... My truck now (2002 2.4 2wd) is running like a top & no need to play "operation"...

Again, see if IAC is getting current & make sure grounds are solid. Even wire brush the terminal, bolt, contact metal & lite sprizz of oil if suspect...

Somebody Pleez chime in!!

Edit: also if alternator rectifier working; I'm aware of headlights working!

 

All checks out it seems. Wondering if anyone has any more ideas or things to check?
Have been unable to find the service manual for my truck. Ttora links don't seems to work.
Still idles around 900 cold and 1100 when warm. Mabey it's time to contact max bore....

 

I'm no help for you on this. I mean I can listen and brainstorm and stuff but never been through similar. One of The guys that really know their stuff with the 2.4 and this kind of stuff is @DrZ
Shoot I think thats his handle, we'll see

 

Can you look at live data ??

I am thinking coolant temp sensor telling The ECM the engine is below temp so it cranks up the idle.

Are you saying as soon as you clear the code then start the engine it comes back ??

As strange as it sounds it almost sounds like The IAC is wired backwards closed at cold engine open when the engine warms up .

these were plug and play ??

Do you still have the first one??

 

Thanks for the reply. Yes my code reader offers live data. Temp seems ok. Replaced temp sensor several months ago. I have both iac valves I replaced. old Oem valve was cruddy and not rotating. They were plug and play.
Unplugging iac has no effect on idle. Seems mabey wiring harness or ecu. to blame?
edit: i reset the code with the engine running and the cel returns within 5 seconds or so. same p0505. i think there are possibly 2 issues going on as the idle has been like this for 2 years and only recently(2 months) did the cel illuminate and idle got abit rougher...

 

My first thoughts are the throttle is not closing correctly/completely. Or you didn't set the TPS correctly so the ECU doesn't know the throttle is at idle position.

The 96 repair manual says for P0505:
IAC valve is stuck or closed
Open or short in lAC valve circuit
Air intake (hose loose)

Since you replaced the IAC a few times maybe it's a problem with the wiring or the air intake hose connected to the IAC.

 

Good call DocZ. If the plug or wiring to the IAC was buggered and not plugging in correctly, or if the little IAC motor had an open, the ECU would detect that very quickly like the OP is saying is happening. And we know it's been moved and messed with, so the plug and wiring inspection/testing sounds like a great place to start

 

And he did a tune up recently, wonder if the air intake and routing is all kosher? Would be worth double checking all of those clamps and unions too

 

Poor seal at the IAC or throttle body sucking air

 

Really appreciate the ideas. Will check voltage at iac connector and all air hoses again. All seemed well each time I pulled the throttle body. After all..it has lives all its life here on the east coast. Mabey I missed a corroded connection.
The tps is new Oem. Didn't know it had an adjustment. Saw the slotted screws but didn't touch them.
I did a freeze frame of live data yesterday. Will report the values when I get home. I remember the old and new tps reported different values..
Thank you again. Wish dx was as straight forward as my acvws! Don't know water cooled cars as well...

 

sorry for delay. grandson came for a visit.
the butterfly closes completely but...there are gaps around it. noticed this the first time i cleaned TB. at that time, i had high idle and no cel. the cel came on 1 1/2 yrs later. thinking i have 2 issues. may try maxbore for the TB rebuild.
took a short drive to store and wrote down the live data. which ones would be helpful ?ect-163, rpm-1283, iat(f)-33
long ft1-11.7, pct-25.1. there are others as well...
thanks again

 

I suspect but can not verify if there is any logic in the IAC circuit to trip that particular code. This is what I am thinking. The throttle body is worn and more air is getting past the closed throttle blade and she has a high idle. This air is being metered by the MAF so the correct amount of fuel is being injected. The crank position sensor is giving the PCM the correct RPM of the motor and the throttle position sensor is telling the PCM that the throttle is closed so the PCM is sending the correct signal to the IAC to close that valve but the RPMS wont come down... the PCM is confused. The logic inside it isnt sophisticted enough for this so it pops that code. This is probably a 2 trip code too... this might explain the seaminly randomness that some people are experiencing.

 

thanks for the info on how this works. took a longer drive today and watched the live data. ect read 177 when driving and 107 when idling. hmm. tps at 11.2 . old tps read 10.6. have replaced thermostat and coolant temp sensor several months ago. no vac leaks with my smoke box, rechecked all the air hoses as well.
mabey its time to ship TB off to maxbore .

 

ECT is coolant temperature? It shouldn't be 107F when idling. It shouldn't fluctuate at all with engine speed and only change gradually in general.

But it does sound more like a problem with the throttle plate gaps. I'm not sure how the ECT readings play into all this.

 

The ECT will be telling the ECM the engine is still cold at 107 degrees