Inspect all vacuum hoses for cracks or disconnection.
2. IAC (Idle Air Control)
The 305 engine uses an IAC motor mounted on the throttle to stabilize idle speed. When this motor fails, it will cause the vehicle to stall in gear. Test to make sure the voltage is going to the motor and that the motor functions correctly.
3. Throttle Position Sensor (TPS)
The throttle position sensor is a component of the fuel injection system that is mounted to the throttle body. It is responsible for providing information to the engine control module (ECM) about the position of the throttle valve. If the TPS is faulty, it can cause the engine to stall when put into gear. To test the TPS, you will need a multimeter and you can follow the steps below:
- Disconnect the electrical connector from the TPS.
- Set the multimeter to volts DC.
- Connect the positive lead of the multimeter to the yellow wire at the TPS connector and the negative lead to the black wire.
- Open the throttle valve slowly. The voltage reading on the multimeter should increase smoothly from 0 volts to 5 volts as you open the throttle.
- If the voltage reading does not increase smoothly or if it does not reach 5 volts when the throttle is fully open, the TPS is likely faulty and needs to be replaced.
4. Fuel Pressure
Make sure there isn’t a restriction with fuel delivery. If there isn’t a fuel filter, then it could be the fuel pump itself. Fuel pressure should be between 9 and 13 psi.
5. Ignition Timing
Ignition timing is another potential culprit for a stalling 305 Vortec. While the ignition system is similar to that of a distributor and coil ignition system, it is somewhat different. If you can adjust the timing correctly the ignition timing will be at 0 TDC.
