Can you bypass the tpc and iac on a 1991 lexis 400 with a cable idle adjustment screw

CHECK IF ANYTHING GOT STACK,CLEAN THROTTLE BODY.CHECK ALL CONNECTION,YOU COULD BET THE PINS!

I would check the IAC motor or idle air control motor, heres a little info.about the part.Stratus Sedan, 1999-2005 Idle Air Control Motor

• DESCRIPTION & OPERATION
• REMOVAL & INSTALLATION

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Description & Operation

Not for Dodge Stratus Sedan
The idle air control motor (IAC) attaches to the throttle body. It is an electric stepper motor. The PCM adjusts engine idle speed through the idle air control motor to compensate for engine load, coolant temperature or barometric pressure changes. The throttle body has an air bypass passage that provides air for the engine during closed throttle idle. The idle air control motor pintle protrudes into the air bypass passage and regulates airflow through it.
The PCM adjusts engine idle speed by moving the IAC motor pintle in and out of the bypass passage. The adjustments are based on inputs the PCM receives. The inputs are from the throttle position sensor, crankshaft position sensor, coolant temperature sensor, MAP sensor, vehicle speed sensor and various switch operations (brake, park/neutral, air conditioning).

Fig.

Not for Dodge Stratus Sedan
When engine rpm is above idle speed, the IAC is used for the following functions:


Off-idle dashpot Deceleration air flow control A/C compressor load control (also opens the passage slightly before the compressor is engaged so that the engine rpm does not dip down when the compressor engages)
The idle air control motor (IAC) attaches to the throttle body. It is an electric stepper motor. The PCM adjusts engine idle speed through the idle air control motor to compensate for engine load, coolant temperature or barometric pressure changes. The throttle body has an air bypass passage that provides air for the engine during closed throttle idle. The idle air control motor pintle protrudes into the air bypass passage and regulates airflow through it.
The PCM adjusts engine idle speed by moving the IAC motor pintle in and out of the bypass passage. The adjustments are based on inputs the PCM receives. The inputs are from the throttle position sensor, crankshaft position sensor, coolant temperature sensor, MAP sensor, vehicle speed sensor and various switch operations (brake, park/neutral, air conditioning).

Fig.

When engine rpm is above idle speed, the IAC is used for the following functions:


Off-idle dashpot Deceleration air flow control A/C compressor load control (also opens the passage slightly before the compressor is engaged so that the engine rpm does not dip down when the compressor engages)
Target Idle
Target idle is determined by the following inputs:


Gear position ECT Sensor Battery voltage Ambient/Battery Temperature Sensor VSS TPS MAP Sensor
Target idle is determined by the following inputs:


Gear position ECT Sensor Battery voltage Ambient/Battery Temperature Sensor VSS TPS MAP Sensor

Removal & Installation

1. Disconnect the negative battery cable.
2. Disconnect the IAC electrical connector.
3. Remove the IAC mounting screws.
4. Remove the IAC.

To Install:

1. Install the IAC to the throttle body.
2. Tighten mounting screws to 5.1 Nm (45 inch lbs.) torque.
3. Attach electrical connector to the IAC.
4. Connect the negative battery cable.
   
   

   Fig.
   

1. Disconnect the negative battery cable.
2. Disconnect the IAC electrical connector.
3. Remove the IAC mounting screws.
4. Remove the IAC.

To Install:

1. Install the IAC to the throttle body.
2. Tighten mounting screws to 5.1 Nm (45 inch lbs.) torque.
3. Attach electrical connector to the IAC.
4. Connect the negative battery cable.

change the idle air control valve.

Idle Air Control (IAC) Valve OPERATION The Idle Air Control (IAC) valve controls the engine idle speed and dashpot functions. The valve is located on the side of the throttle body. This valve allows air, determined by the Powertrain Control Module (PCM) and controlled by a duty cycle signal, to bypass the throttle plate in order to maintain the proper idle speed. Fig. 1: Typical Idle Air Control (IAC) valve which is mounted to the throttle body - cutaway view shows air bypass direction
--- REMOVAL & INSTALLATION

1. Disconnect the negative battery cable. To remove the IAC valve, first disconnect the negative battery cable, then the IAC wire harness plug
   Next, remove the two IAC valve attaching bolts . . .
   . . . and pull the valve from the intake manifold
   
   
2. Disengage the wiring harness connector from the IAC valve.
3. Remove the two retaining screws, then remove the IAC valve and discard the old gasket. To install: When installing the valve, always discard the old gasket and install it using a new one
   
   
4. Clean the IAC valve mounting surface on the throttle body of old gasket material.
5. Using a new gasket, position the IAC valve on the throttle body. Install and tighten the retaining screws to 71-106 inch lbs. (8-12 Nm).
6. Attach the wiring harness connector to the IAC valve.
7. Connect the negative battery cable.

you need to clean your idle air control valve ( or replace it) Spray carb cleaner does a nice job of cleaning it.

This tutorial is from autozone.com

OPERATION

The Idle Air Control (IAC) is a bi-directional motor driven by two coils. The purpose of the IAC valve is to control engine idle speed, while preventing stalls due to changes in the engine load. The IAC valve, mounted in the throttle body, controls bypass air around the throttle plate. The PCM controls engine idle speed by adjusting the position of the IAC motor pintle. The PCM pulses current to the IAC coils in small steps (counts) to extend the pintle into a passage in the throttle body to decrease air flow. The PCM reverses the current pulses to retract the pintle, increasing air flow. This method allows highly accurate control of idle speed and quick response to changes in engine load. If RPM is too low, the PCM will retract the IAC pintle, resulting in more air being bypassed around the throttle plate to increase RPM. If the RPM is too high, the PCM will extend the IAC pintle, allowing less air to be bypassed around the throttle plate, decreasing RPM.

Fig. Typical Idle Air Control (IAC) valve components
During idle, the proper position of the of the IAC pintle is calculated by the PCM based on the battery voltage, coolant temperature, engine load and engine RPM. If the RPM drops below a specified value, and the throttle plate is closed (TP sensor voltage is between 0.20-0.74), the PCM senses a near stall condition. The PCM will then calculate a new IAC pintle position to prevent stalls.
If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset. The IAC resets when the ignition switch is cycled ON and then OFF . When servicing the IAC, it should be disconnected or connected with the ignition switch OFF in order to keep from having to reset the IAC valve.
The position of the IAC pintle affects engine start up and the idle characteristics of the vehicle. If the IAC pintle is fully open, too much air will be allowed into the manifold. This results in high idle speed, along with possible hard starting and a lean air/fuel ratio. A Diagnostic Trouble Code (DTC) may set. If the IAC pintle is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed, along with hard starting and a rich air/fuel ratio. Again, a Diagnostic Trouble Code (DTC) may set. If the IAC pintle is stuck part way open, the idle may be high or low and will not respond to changes in engine load.

TESTING

As with most all engine control sensors used in your vehicle, a thorough and proper test can only be performed by a qualified technician using a scan tool to read the data stream from the PCM. There are a few items a non-professional should check before taking the vehicle to a qualified technician for diagnosis and repair.

Check for a poor connection at the PCM or IAC motor. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connection. Inspect for a damaged wiring harness, especially if heavy work has recently been performed (intake manifold removal, engine removal, etc.) where the throttle body has been disturbed. Inspect for a restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element or foreign objects blocking the air intake system. Inspect the throttle body. Check for objects blocking the IAC passage or throttle bore. Excessive deposits, especially on high-mileage engines, can build up in the IAC passage and on the IAC pintle. Excessive deposits can also build up on the throttle plate, so check for a sticking throttle plate. Check for vacuum leaks such as disconnected hoses, leaks at the EGR valve and EGR pipe to the intake manifold, leaks at the throttle body, faulty or incorrectly installed PCV valve, leaks at the intake manifold brake booster hose connection, etc.

REMOVAL & INSTALLATION

1. Disconnect the negative battery cable.
2. Detach the electrical connector from the IAC valve.
3. Remove the 2 attaching screws and remove the IAC valve from the engine. Remove the O-ring from the housing.

To install:

Fig. The Idle Air Control (IAC) valve is mounted on the throttle body-3.8L (VIN K) engine shown, others similar

NOTE Before installing a new IAC valve, measure the distance that the valve is extended. The measurement should be made from the motor housing to the end of the valve cone (pintle). The distance should be no greater than 1 1 / 8 inch (28mm). If the pintle is extended too far, adjustment is required, otherwise damage may occur when the IAC valve is installed. Adjust the IAC valve by compressing the pintle to achieve the correct length.

1. Use a new O-ring, install the IAC valve and tighten the retaining screws to 18 inch lbs. (2 Nm).
2. Attach the electrical connector.
3. Connect the negative battery cable.
4. The PCM will reset the IAC valve the next time the ignition switch is turned ON and then OFF .
5. Start the engine and allow to warm to operating temperature to check idle quality.

OPERATION The Idle Air Control (IAC) valve controls the engine idle speed and dashpot functions. The valve is located on the throttle body on. This valve allows air to bypass the throttle plate. The amount of air is determined by the Powertrain Control Module (PCM) and controlled by a duty cycle signal. Fig. 1: Cleanable IAC valve — 5.0L engine version shown, others similar
Fig. 2: Non-cleanable IAC valve — 5.0L engine version shown, others similar
TESTING OBD-I System

1. Make sure the ignition key is OFF.
2. Disconnect the air control valve.
3. Use an ohmmeter to measure the resistance between the terminals of the valve solenoid. NOTE: Due to the diode in the solenoid, place the ohmmeter positive lead on the VPWR pin and the negative lead on the ISC pin.
   
4. If the resistance is not 7–13 ohms, replace the air control valve.

---
REMOVAL & INSTALLATION Fig. 1: Idle air control valve mounting — 4.9L engine version shown, others similar

1. Disconnect the negative battery cable.
2. Disconnect the engine wiring to the IAC sensor.
3. Remove the two retaining screws for the valve.
4. Remove the IAC valve and discard of the old gasket. Fig. 2: Disengage the idle air control solenoid electrical connection
   Fig. 3: Loosen the idle control solenoid retaining screws
   Fig. 4: Remove the idle air control solenoid from the throttle body
   To install:
   
5. Clean the area of old gasket material.
6. Using a new gasket, attach the IAC valve to the engine. Tighten the retaining screws to 71–102 inch lbs. (8–12 Nm).
7. Connect the IAC valve wiring to the unit.
8. Connect the negative battery cable.

Operation

The Idle Air Control (IAC) valve adjusts the engine idle speed. The valve is located on the side of the throttle body. The valve is controlled by a duty cycle signal from the PCM and allows air to bypass the throttle plate in order to maintain the proper idle speed. Do NOT attempt to clean the IAC valve. Carburetor tune-up cleaners or any type of solvent cleaners will damage the internal components of the valve.
The Idle Air Control (IAC) valve adjusts the engine idle speed. The valve is located on the throttle body. The valve is controlled by a duty cycle signal from the PCM and allows air to bypass the throttle plate in order to maintain the proper idle speed.
Removal & Installation

1. Disconnect the negative battery cable.
2. Detach the IAC solenoid connector.
3. Remove the two retaining bolts and remove the IAC solenoid and gasket from the throttle body.
4. Installation is the reverse of the removal procedure. Use a new gasket and tighten the retaining bolts to 71-97 inch lbs. (8-11 Nm).

its located on the throttle body connected to your air intake manifold where your throttle cable connects on the throttle body there is a adjustment screw connected there

Look for a small electric motor near the accelerator cable and near the top of the valve cover.

It's call IDLE AIR CONTROL (IAC) motor.

It's job is to increase the idle when load is added.
Example: turning on headlight,turning on AC.

Testing it is simple.

Warm up you car for 10 minutes.

Locate the IAC motor

turn on loads.....AC,headlights,etc


The motor should move the idle up


If the motor does not increase the RPM then it can be stick.

Try to give it few gentle taps to free up the gears.

It can be clean if your are up to it.


This electrical motor is very expensive. Please handle it with care.

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The other trouble spot are

old accelerator cable

TPS Throttle position sensor

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I will do a simple tune up and gas treatment before starting to replace any parts.


Please post reply on the comment window.

The idle on these is controlled electronically by an IAC solenoid (idle air control). Adjusting the screw will not do anything to adjust your idle down. Chances are you could have a vacuum leak, or a faulty IAC solenoid. I would start by checking for vacuum leaks.

THE DISTRIBUTOR WILL CAUSE THIS PROBLEM IN A HONDA TRY A KNOWN GOOD ONE .