No high idle on a cold start (1 Viewer)

[Vasiliy]

Hi everyone. Since almost two year with this problem, I gived up and want try ask for a help here.
I have JDM LC80 93y with 1fz-fe AT. In the past I had high cold start idle like everyone, even done o-ring mod but suddenly one fine day it went.

Problem is happens every cold engine start, it won't keep high startup idle for fasting warm-up, no matter if is 5F or 86F outside, switch A/C On can increase idle, shifting P-R-N-D also increase idle too.

I have OBD1 Bluetooth device that connecting to smartphone, I can see full open IAC 125step. Usually after starting it's 70-60step for 1000-900-850RPM and slowly going down, it's can stay at 850-800RPM longer with 66-50-45step and only near to 40 step quickly decrease to a nominal idle of 650 RPM with 20-18 step.
I know, looks like pretty vacuum leak, leaning on low VAF 2-15-2-35 voltage at idle and low IAC step but I hooked hand-made smoke pump, and couldn't fine anything horrible, maybe I need check another more time.

Here is one cold start at winter from the past, I could feel unburned gasoline smell for a while maybe 1 minute.
THW 14F |. VAF 1.29V. |. RPM 875. |. IAC 86 step
after 8 minutes of warming
THW 113F. |. VAF 1.72V. |. RPM 800. |. IAC 58 step
Looks strange, because VAF show less air and IAC step close more, but idle speed the same?

And some more log
THW 78.8F | VAF 1.60V | RPM 850 | IAC 60 step
THW 89.6F. |. VAF 1.58V |. RPM 925. |. IAC 64 step
THW 80.6F |. VAF 1.52V. |. RPM 1000 |. IAC 67 step
THW 104F. |. VAF 1.76V. |. RPM 825. |. IAC 53 step
THW 64.4F. |. VAF 156V. |. RPM 850. |. IAC 65 step
THW 140F. |. VAF 1.92V | RPM 750. |. IAC 53 step
THW 62.7F |. VAF 1.45V. |. RPM 1025. |. IAC 78 step
THW 55.4F. |. VAF 1.43V. |. RPM 1000. |. IAC 80 step
THW 51.8F |. VAF 1.45V. |. RPM 850. |. IAC 79 step
THW 39.2F. |. VAF 1.45V. |. RPM 825 |. IAC 79 step

Now what have I done with car
TPS adjusted with IDL signal, disconnecting IAC connector got 2k RPM at cold start with 60-65 IAC step.

* 1 removing and cleaning throttle body, IAC, intake plenum, injectors (with new gasket kit), sealant intake manifold & throttle body
* 2 changed little vacuum hoses, PCV valve with gasket and hose, intake hose, bypass EGR
* 3 changed air filter, gasoline filter underhood, sparks, OX sensors, charcoal canister
* 4 checking ignition wires, distributor cap and rotor, looks in good shape, changed few years ago
* 5 trying and changing for a good used one, ECU, throttle body, 3 different IAC valve, 4 different TPS sensor, 3 engine coolant sensor, 1 VAF meter
* 6 servicing starter, alternator, neutral safety switch

Thanks and sorry for poor English, cheers

 

[Desert Dino]

How is your warm idle?

When did you last reset the ECU and let it relearn the parameters?

You can always instal hand throttle to help you

 

[Vasiliy]

My warm idle - 650. Resetting ECU doesn't help, in the past if I disconnect battery idle was always bad and shaking, but now it don't do that. I'm sure here is some sensor that say ECU reduce IAC steps, because it's always the same, it's programmed. Hand throttle can't help, I have cruise control, so I think here is no empty place for cable

 

[ppc]

What happens when you disconnect all three cables from the throttle body?

 

[Desert Dino]

A hand T cable connected to the gas pedal inside cabin

Most 80 have cruise control

 

[Vasiliy]

What happens when you disconnect all three cables from the throttle body?

I did it before, have no effect

A hand T cable connected to the gas pedal inside cabin

Most 80 have cruise control

I see, that will be easier way as last try, but wish I could fix it without adding hand throttle, cuz I like to start car when is cold with my remote control and sit in car when it already hot ( you know, cold leather is not good for **s and not only...) so IAC cold control is better

Ok, I done some more troubleshooting.
I disconnected THW pin from ECU connector and added another wire, for testing inside cabin.
I have 2 spare ex-used ECT sensor,
Multimeter test ECT sensor is disconnected from ECU:
ECT1- 2.55Om,
ECT2- 2.65Om,

ECT sensor is connected to ECU pins THW-E2, igsw OFF:
ECT1- 1.43Om,
ECT2- 1.45Om,

ECT sensor is connected to ECU pins THW-E2, igsw ON:
ECT1- 1.93V,
ECT2- 1.96V,
Questions is- while sensor is connected to ECU with E2 ground, it show 1.96v which is mean 77-78F, but disconnected from ECU is 2.65Om which mean near 14F. But while sensor is connected to another ground (E1) or body ground, both Om and Voltage match each other