Poor Idling

High Idle Speed

• Check A/C compressor signal circuit. See appropriate AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.
• Check ECM power source circuit. See ELECTRONIC CONTROL MODULE (ECM) POWER SOURCE CIRCUIT under COMPUTERIZED ENGINE CONTROLS in appropriate SYSTEM & COMPONENT TESTING article.

Low Idle Speed

• Check A/C compressor signal circuit. See appropriate AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING.
• On all models except Camry CNG, Land Cruiser and Tundra V8, check fuel pump control circuit. See FUEL PUMP CONTROL CIRCUIT under COMPUTERIZED ENGINE CONTROLS in appropriate SYSTEM & COMPONENT TESTING article. On Land Cruiser, perform DTC P1200: FUEL PUMP RELAY/ECU CIRCUIT test in SELF-DIAGNOSTICS - LAND CRUISER article. On Camry CNG, check fuel shutoff valve circuit. See DTC P1190: FUEL PRESSURE REGULATOR MALFUNCTION test in SELF-DIAGNOSTICS - CAMRY CNG article. On Tundra V8, check fuel pump control circuit. See DTC P1200: FUEL PUMP RELAY CIRCUIT test in SELF-DIAGNOSTICS - TUNDRA V8 article.

Rough Idle

• Check engine compression. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
• On all models except Camry CNG, Land Cruiser and Tundra V8, check fuel pump control circuit. See FUEL PUMP CONTROL CIRCUIT under COMPUTERIZED ENGINE CONTROLS in appropriate SYSTEM & COMPONENT TESTING article. On Land Cruiser, perform DTC P1200: FUEL PUMP RELAY/ECU CIRCUIT test in SELF-DIAGNOSTICS - LAND CRUISER article. On Camry CNG, check fuel shutoff valve circuit. See DTC P1190: FUEL PRESSURE REGULATOR MALFUNCTION test in SELF-DIAGNOSTICS - CAMRY CNG article. On Tundra V8, check fuel pump control circuit. See DTC P1200: FUEL PUMP RELAY CIRCUIT test in SELF-DIAGNOSTICS - TUNDRA V8 article.

Surging

• Check ECM power source circuit. See ELECTRONIC CONTROL MODULE (ECM) POWER SOURCE CIRCUIT under COMPUTERIZED ENGINE CONTROLS in appropriate SYSTEM & COMPONENT TESTING article.
• On all models except Camry CNG, Land Cruiser and Tundra V8, check fuel pump control circuit. See FUEL PUMP CONTROL CIRCUIT under COMPUTERIZED ENGINE CONTROLS in appropriate SYSTEM & COMPONENT TESTING article. On Land Cruiser, perform DTC P1200: FUEL PUMP RELAY/ECU CIRCUIT test in SELF-DIAGNOSTICS - LAND CRUISER article. On Camry CNG, check fuel shutoff valve circuit. See DTC P1190: FUEL PRESSURE REGULATOR MALFUNCTION test in SELF-DIAGNOSTICS - CAMRY CNG article. On Tundra V8, check fuel pump control circuit. See DTC P1200: FUEL PUMP RELAY CIRCUIT test in SELF-DIAGNOSTICS - TUNDRA V8 article.