I cannot locate the idle control sensor - 1990 Lexus LS 400

under hood look where the throttle cable connects behind it u will see a black looking module thats the throttle sensor the idle control is located just to the rite toward the filter as the mass sensor is there too

Why are you convicting the idle control valve? was it properly diagnosed? Could be coolant sensor, intake sensor,O2 sensors etc. Check it out first.

What your Explorer has is actually called the EEC-IV. It is sort of like an ECU. The EEC stands for "Electronic Engine Controls". Your EEC-IV Does this:

• Powertrain Control Module (PCM)
  
• Throttle Position (TP) sensor
  
• Mass Air Flow (MAF) sensor
  
• Intake Air Temperature (IAT) sensor
  
• Idle Air Control (IAC) valve
  
• Engine Coolant Temperature (ECT) sensor
  
• Heated Oxygen Sensor (HO2S)
  
• Camshaft Position (CMP) sensor
  
• Knock Sensor (KS)
  
• Vehicle Speed Sensor (VSS)
  
• Crankshaft Position (CKP) sensor
  
  

The EEC microcomputer circuit processes the input signals and produces output control signals to the fuel injectors to regulate fuel discharged to the injectors. It also adjusts ignition spark timing to provide the best balance between driveability and economy, and controls the IAC valve to maintain the proper idle speed.
The EEC is located in the engine compartment. Post your engine size and I can tell you where it's at.

Error Code: P0130
Fault:
Oxygen Sensor (O2S) 1, Bank 1 - Circuit Malfunction
Possible Cause:
Malfunction Indicator Lamp (MIL) Triggered on first occurrence.
-Wiring harness.
-Oxygen sensor (O2S).
-Engine control module (ECM).

Error Code: P0505
Fault:
Idle Speed Control (ISC) System - Malfunction
Possible Cause:
-Wiring harness.
-Idle speed control (ISC) actuator/Idle air control valve (IAC) valve.
-Throttle motor.
-Throttle valve tight/sticking.
-Engine control module (ECM).

Error Code: P0100
Fault Location:
-Mass Air Flow (MAF) Sensor/Volume Air Flow (VAF) Sensor - Circuit --Malfunction
Possible Cause:
-Wiring harness.
-Mass air flow (MAF) sensor.
-Volume air flow (VAF) sensor.
-Engine control module (ECM).

Error Code: P1491
Fault:
Exhaust Gas Recirculation (EGR) Valve Insufficient Lift
Possible Cause:
-Wiring harness.
-EGR Valve.
-ECM

Error Code:P1607
Fault:
-Engine Control Module (ECM)/Powertrain Control Module (PCM)

Error Code: P0966
Location:
-Pressure Control (PC) Solenoid B - Circuit Low
Possible Cause:
-Wiring short to earth.
-Pressure control (PC) solenoid.
-Engine control module (ECM)/Powertrain control module -(PCM)/Transmission control module (TCM) .

you did'nt specify what year the vehicle is,but i suspect a bad idle control sensor. located on the intake manifold. usually. the cost of part is around 20.00 and replacement involves removing 2 bolts. just disconnect the battery before the replacement.autozone can assist with the location with a print out on paper,or advance auto,o'reilleys auto parts. all should be able to print it out for you with parts location and should be able to explain how to replace it. the rough idle up and down describes a bad idle control sensor,but if you want to be sure,,have them code read your cars computer for free just to be sure. it is a free service. thank you for choosing fixya.com!

It sounds to me like you have replaced everything except the most likely cause of your idle control problem...The Idle Air control. (IAC) (or Idle Speed Control Valve) It is located onthe throttle body and looks like the picture below.

no idle control sensor but it has both an IAC, idle air control valve and a T, throttle position sensor
both are located at the throttle body

Knock Sensor - is not an issue
O2 Sensor-just sees the condition of exhaust, during the stall & sets a code

I would look at the Idle Speed Motor, TPS Sensor,even vacuum leaks,Egr Valve.
Don't know your veh systems, Hope that helps some.

The idle of the vehicle is controlled by the idle air control motor located on the throttle body looks like a little barrel with a plug in on the end bolts to the throttle body.

It could be a faulty idle speed control valve