Rough idle then shuts off

TODDAKINS

MEMBER
1990 TOYOTA PICKUP
3.0L
V6
2WD
AUTOMATIC
200,000 MILES

For some unknown reason one day I stopped and my truck quit running. When I start it up it will not idle and then shuts off. Still have 100% power. I have replace my timing belt all pulley's, water pump, fuel filter, plugs, wires, cap, rotor, replaced all vacuum lines, found a vacuum leak replaced intake manifold gasket problem solved. No water in the oil, no oil in the radiator, no steam out of my exhaust, radiator does not lose any water. Now my truck will idle with the air conditioner on and even then it doesn't want to. I can keep it alive and drive it with the A/C on but I still have to slightly touch the accelerator to keep it alive when I stop. Does anybody out there have any idea what is wrong with my truck? Please help

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,645 POSTS

Hi,

When you turn the AC on, the idle speed is controlled by a vacuum switching valves (VSV). Whenever the ECU senses activation of the air conditioning compressor, the Idle-up VSV is activated to increase base idle speed. The Idle-up VSV is a calibrated air bleed around the throttle valve and feeds air to the engine through vacuum hoses. Note that this is responsible for idle speed without the AC as well.

First, make sure the vacuum hoses to the VSV are in good condition and not leaking or damaged. If everything looks good, follow this diagnostic chart for checking it. The attached pics correlate with the directions.

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1990 Toyota Truck Pickup 2WD V6-180.5 2959cc 3.0L SOHC (3VZ-E)
Component Tests and General Diagnostics
Vehicle Powertrain Management Fuel Delivery and Air Induction Idle Up Control Valve Testing and Inspection Component Tests and General Diagnostics
COMPONENT TESTS AND GENERAL DIAGNOSTICS
1. Disconnect and remove the VSV from the engine.
2. Using an Ohmmeter, check the resistance between the terminals.
Testing VSV For Open Circuit

pic 1

RESISTANCE (COLD): 33 - 39 ohms

3. Check for continuity between the case and either terminal.
Testing VSV For Short Circuit

Pic 2

4. If windings are grounded to case or terminal resistance is not as specified, replace the VSV.
5. Blow through pipe E and check that NO air flows from pipe F.
Testing VSV Operation - Current Removed

pic 3

6. Apply battery current to the VSV and check that air flows through pipe E and F.
Testing VSV Operation - Current Applied

pic 4

7. If a problem is found, replace the VSV.
8. Reinstall VSV on the engine and reconnect vacuum hoses.

_________________________________________

Also, you can adjust the curb idle speed. Here are the directions. If it is just slightly low, follow these directions.

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1990 Toyota Truck Pickup 2WD V6-180.5 2959cc 3.0L SOHC (3VZ-E)
Curb Idle Speed
Vehicle Powertrain Management Fuel Delivery and Air Induction Idle Speed Adjustments Curb Idle Speed
CURB IDLE SPEED
Tachometer Hookup

pic 5

Fig. 213 Idle Speed Adjusting Screw

pic 6

1. When setting the idle speed make sure that:
a. Air cleaner is installed.
B. All vacuum hoses are connected.
C. Make sure that all fuel injection wiring connectors are fully plugged in.
D. Engine should be at normal operating temperature.
E. All accessories should be turned off and the transmission in neutral.
2. Connect a tachometer to the engine, Fig. 211

NOTE: Never allow the tachometer terminal to contact a ground as this could cause damage to the ignition system. Some tachometers are not compatible with this ignition system, so please confirm the compatibility of your tachometer before connecting it to vehicle.

3. Run engine at 2,500 rpm for about 2 minutes.
4. Set the idle speed by turning the idle speed adjustment screw, Fig. 213.

IDLE SPEED: 800 rpm

5. Remove tachometer.

_________________________________________

Let me know if this helps or if you have other questions.

Take care,
Joe

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