need help 98 tacoma 3.4 5spd code p0505

I have a 98 tacoma 3.4 5spd manual 4x4 .has a code p0505 i cannot figure out .So i went through toyota diagnostics ,after operating temp all accesories off jumper te1 and e1 idle rose more than 100rpm then say go to step 6) check air induction system so i smoke tested found no leaks then states open or short in AC switch signal circuit may exist check ac amplifier .i cannot find any testing or diagnostics for AC amplifier and would that cause my issue.any help would be appreciated .I have been fighting the p0505 things i have tried before i went through toyota diag replaced iac twice,smoke tested,cleaned throttle body/iac replaced throttle body gasket,checked continuity of iac ok.I am having trouble figuring it out truck idles around 950rpm engine light on sometimes dies.I would like to get back to factory specs with no engine light on.thank you

 

None of the vacuum lines are dry rotted?

 

so i did this diagnostics 1) jumped 100 rpm went to 6) smoke tested ok disabled AC cleared code came right back.Decided to check 2) ecm had battery volts both circuits ok.IAC tested good and replaced with a new one no change, so 5) says throttle body or ecm i did notice when i lit up the back of the throttle body there was a lot of light shining past throttle plate.so were im at now is something with AC circuit or throttle body or ecm any ideas or test to rule them out

 

I smoke tested nothing leaking

 

think this would cause p0505

 

The throttle body could use some work though in most cases it would give you a higher then normal idle.

Have you checked your coolant temp sensor??

If the ECM does not know the correct engine temperature it will not open or close the IAC tripping the code.

 

the vehicle at operating temp is 190 so i would assume its good.i will check it out thank you

 

the idle warm is 900-950 so it is high.if i unplug iac jumps to aprox 1200

 

so plugged throttle body and started idled at 650 700 but did not take care of the p0505 .i have tested everything.going to get a ecm from all the factory toyota tests ive done all points to the ecm .thanks for the help

 

Did you end up replacing your ECU?

I am having the same issue with a 97 all checks point to the ECU. This particular ECU I repaired a year ago for other issues, so I think this will solve the problem. Curious if it worked out for you.

 

Throttle body looks like it needs a rebore. Lots of light shinning thru.

 

yes the ecm took care of my 505 code.

 

Thanks for the reply.

I also went through the diagnostic procedure. The iac tests good it will open and close when jumping it. There are no shorts in the wiring. But the ecu will not raise the idle.

If I unplug the iac the idle will go up to ~1500 rpm.

I’m looking into buying a refurbished ecu.