Diagnosing Fuel Quality Problems

Symptoms 

A fuel-quality problem may be indicated by the following driveability symptoms:

• Spark knock/detonation
• Hard cold start and garage stalls
• Poor cold performance
• Tip-in hesitation, sag, or stumble (momentary lack of response during initial acceleration)
• Surges and/or chuggles
• Lack of power, sluggish, or spongy
• Cut out or misses
• Rough/unstable idle (intake or exhaust valve deposits)