Go to Symptom Troubleshooting

Symptom #10 - Engine stalls, runs rough, misses, bucks, hesitates or surges

Description

• Engine stops unexpectedly at beginning of acceleration or during acceleration
• Engine stops unexpectedly while cruising
• Engine speed fluctuates during acceleration or while cruising
• Engine misses during acceleration or cruising
• Vehicle bucks or jerks during acceleration, while cruising, or upon deceleration
• Momentary pause at the beginning of acceleration or during acceleration
• Momentary minor irregularity in engine output

Possible Causes

• Air leakage from intake-air system parts
• Improper operation of idle air control valve
• Crankshaft sensor circuit malfunction
• Camshaft sensor circuit malfunction
• Spark leakage from ignition coil
• PCV valve malfunction
• Restriction in exhaust system
• Open or short circuit in fuel pump and related harness
• Improper fuel pressure
• Fuel leakage from injector
• Improper A/C system operation
• Purge solenoid valve malfunction
• EGR valve malfunction
• EGR solenoid malfunction
• Low engine compression
• Vacuum leakage
• Fuel pump control relay and resistor
• Poor fuel quality
• Air filter restriction
• Electrical connector disconnection
• No battery power supply to ECU or poor ground
• Fuel pump mechanical malfunction
• Clogged injector

Diagnostic Procedure

1.  Verify vacuum hose connections, check the air filter, check for leakage or restriction of the intake-air system, ensure proper sealing of intake manifold and components attached (e.g. EGR, IAC), examine ignition components, fuel quality, and electrical connections.  Are all items okay?

• Yes - Go to next step
• No - Service as required.

2.  Check for stored OBD-II error codes.  Are there any stored codes?

• Yes - Go to appropriate DTC test
• No - Go to next step

3.  Is engine overheating?

• Yes - Go to Symptom #10 for "engine overheats"
• No - Go to next step

4.  Connect an OBD-II scan tool capable of logging sensor output and drive the vehicle.  Are engine speed (RPM), mass-airflow (MAF), throttle position (TP), and vehicle speed (VSS) PIDs within specifications?

• Yes - Go to next step
• No - Inspect crankshaft position sensor (RPM) circuit, mass airflow sensor (MAF) circuit, throttle position sensor (TP) circuit, and vehicle speed sensor (VSS) circuit.

5.  Visually inspect the crankshaft position sensor and the teeth on the crankshaft pulley.  Are these components okay?

• Yes - Go to next step
• No - Service as required

6.  Measure the gap between the crankshaft position sensor and the teeth of the crankshaft pulley (specification: 0.5-1.5mm).  Is the gap within specification?

• Yes - Go to next step
• No - Adjust crankshaft position sensor

7.  Check spark plug condition.  Are spark plugs wet, grayish white, or covered with carbon soot?

• Yes - If wet or sooty, check for leaky fuel injector
• No - Install spark plugs on original cylinders then go to next step

8.  Remove PCV valve and shake PCV valve.  Does the valve rattle?

• Yes - Go to next step
• No - Replace PCV valve

9.  Verify that the throttle lever is resting on the throttle valve stop screw and/or throttle valve orifice plug.  Are there any faults present?

• Yes - adjust as necessary
• No - Go to next step

10.  Is there an exhaust restriction?

• Yes - Inspect exhaust system
• No - Go to next step

11.  Check fuel pressure between fuel filter and fuel rail.  Connect a jumper wire between the F/P terminal at the engine bay DLC connector and ground.  Is the fuel line pressure within specification (280-330kPa or 41-48psi) with the ignition switch on?

• Yes - Go to next step
• No - If there is no or low pressure, check the fuel pump circuit, control relay and resistor, fuel pump relief valve as well as for fuel leakage inside the fuel pressure regulator and for a restricted main fuel line.  If the fuel pressure is too high, check the fuel pressure regulator, the fuel pump control relay and resistor, and for a clogged fuel return line

12.  Does fuel pressure increase when the accelerator is depressed?

• Yes - Go to next step
• No - Examine the fuel pressure regulator control (PRC) solenoid

13.  Skip to the next step if the symptom occurs with or without the A/C running.  If symptom occurs only with A/C operation, connect a pressure gauge to the A/C line and measure both low and high side pressures.  Are the pressures within specifications?

• Yes - Go to next step
• No - Check the refrigerant charging amount, A/C pressure switch operation, condenser fan operation, and the A/C relay

14.  Skip to the next step if the symptom  occurs with or without cruise control operation.  If symptom occurs only during cruise control operation, inspect the cruise control system.  Is cruise control system operating properly?

• Yes - Go to next step
• No - Repair cruise control system

15.  Is the evaporative emissions purge control system okay?

• Yes - Go to next step
• No - Check if purge control solenoid sticks open mechanically.  Inspect the evaporative emissions control system.

16.  Visually inspect the camshaft pulley, is the camshaft pulley okay?

• Yes - Go to next step
• No - Replace camshaft pulley

17.  With the engine idling, disconnect the vacuum hose from the EGR valve and plug it.  Is the engine condition improved?

• Yes - Check for a stuck EGR solenoid vacuum valve, vent valve, and solenoid valve connector terminals
• No - Check if the EGR valve moves smoothly. If yes, go to next step.  If no, replace the EGR valve

18.  Is the air-bypass valve actuator okay?

• Yes - Go to next step
• No - Replace air-bypass valve actuator

19.  Check engine compression with a cylinder compression test tool.  Is the engine compression within specifications?

• Yes - Verify valve timing and transmission operation
• No - Check for cause

20.  Verify test results.  If okay, return to diagnostic index to service any additional symptoms.  If vehicle is repaired, troubleshooting is complete.  If vehicle is not repaired or additional diagnostic information is not available, replace the ECU.