Fuel System Checks

Check to determine if a lean system causes the condition. Drive vehicle at the speed of the complaint. Monitoring the Fuel Trim will help identify the problem. If the system is lean, the Long Term Fuel Trim will be more than 20 percent.
Check the fuel pressure. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article.
Check fuel injectors. Perform Fuel Injector Coil Test procedure and the Fuel Injector Balance Test procedure. See FUEL INJECTOR COIL TEST - ENGINE COOLANT TEMPERATURE BETWEEN 50-95°F (10-35°C) and FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article.
Check for inferior quality fuel and the proper octane rating. See ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article. Fill fuel tank with a known high quality fuel that meets the vehicles minimum octane requirements. Road test vehicle and re-evaluate vehicle performance.