Engine Poor DRIVEABILITY

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

• Perform the following preliminary checks:
  • Vacuum lines (routing, integrity).
  • Air filter (restricted).
  • Intake air tubes (leaks, restrictions).
  • Proper sealing of intake manifold and components attached to intake air (such as EGR valve or IAC valve).
  • Ignition wiring.
  • Fuel quality (concerns such as proper octane, contamination, winter/summer blend).
  • Electrical connections.
  • Be aware of the over RPM and speed limiting functions of the PCM.
• Are all checks OK? 

• Does engine now stall at idle in Park/Neutral? 

• Does engine idle rough in Park/Neutral? 

• Are any DTCs displayed during Continuous Memory, Key ON, Engine OFF (KOEO) or Key ON, Engine Running (KOER) Self Tests? 

• Retrieve and record Continuous Memory DTCs.
• Perform KOEO Self Test.

  See ON-BOARD DIAGNOSTIC TESTS .

• Are any DTCs displayed? 

• Attempt to start engine at part throttle.
• Does engine start and run smoothly at part throttle? 

• Retrieve and record Continuous Memory DTCs.
• Perform KOEO Self Test,

  See ON-BOARD DIAGNOSTIC TESTS .

• Are any DTCs displayed? 

• Start engine and let idle.
• While checking for RPM drop or engine stall, disconnect IAC valve.
• After testing turn key off and reconnect IAC valve.
• Did RPM drop or engine stall when the IAC valve was disconnected? 

• Reconnect NGS Tester.
• Check following PIDS.
  • DPFEGR, ECT, IAC, LONGFT1, LONGFT2, VPWR.

    See PIN VOLTAGE/PID VALUE CHARTS article .

  • Are PIDS within specification? 

• Is strong blue spark visible at each disconnected high-tension lead while cranking engine? 

• See TEST 8: CRANKSHAFT POSITION (CKP) SENSOR .

CMP sensor.

• CAMSHAFT POSITION (CMP) SENSOR MALFUNCTION .

• Perform fuel pressure INSPECTION.

  See TEST 11: FUEL LINE PRESSURE / FUEL PRESSURE HOLD INSPECTION .

• Fuel line pressure:
  • 386-496 kPa (3.9-5.0 kgf/cm² , 56-72 psi), flexible fuel 380-517 kPa (3.8-5.2 kgf/cm² , 55-75 psi)
  • Is fuel pressure correct? 

See FUEL PUMP in REMOVAL, OVERHAUL, AND INSTALLATION article in Engine Performance .

If pressure is less than 56 (55 flexfuel) psi: Check fuel supply line for restriction.

See TEST 11: FUEL LINE PRESSURE / FUEL PRESSURE HOLD INSPECTION

• Check fuel pump fuel flow,

  See TEST 5: FUEL DELIVERY SYSTEM .

• Did fuel system flow the required amount of fuel? 

See TEST 12: FUEL INJECTOR INSPECTION . If injector leaks, see FUEL RAILS & INJECTORS in REMOVAL, OVERHAUL, & INSTALLATION article in Engine Performance. If injector OK, go to step 13.

See EXHAUST SYSTEM CONCERNS .

• Is there a restriction in the exhaust system? 

• Remove PCV valve and shake it.
• Does PCV valve rattle?

• Start engine and bring to normal operating temperature. Disconnect crankcase ventilation hose from throttle body. Place a stiff piece of paper over the hose. Wait one minute.
• Does vacuum hold paper in place? 

• If vehicle has manual transmission, go to step 17. See DIAGNOSIS - 4R44E or DIAGNOSIS - 5R55E for automatic transmission concerns.
• Is automatic transmission OK? 

• Check EVAP system.
  • If symptom is "engine stalls"

  See CANISTER VENT (CV) SOLENOID MALFUNCTION step 8.

  • For other symptoms, see EVAPORATIVE EMISSION (EVAP) SYSTEM MALFUNCTION step 1.
  • Is a fault indicated? 

• Check engine compression.

  See ENGINE COMPONENT TESTS .

• Is engine compression correct? 

• Check intake air system (for the following symptoms only: Stalls/quits at idle, runs rough at idle, rolling idle or symptoms associated with a sticking throttle body)

  See LOW IDLE / STALLS DURING DECELERATION .

• Is a fault indicated? 

• Additional checks:
• Driveline.
• Transmission/clutch (M/T).
• Charging system.
• A/C system (for surge with A/C on).
• Cruise control system (for surge with cruise control on).
• A/C compressor diode (for rolling idle and/or stumble when A/C cycles on).
• Are the checks OK? 

• Verify test results. If OK,

See DIAGNOSTIC INDEX  to service any additional symptoms