Home › Forums › Stay Dirty Lounge › Service and Repair Questions Answered Here › Rich (negative long term fuel trim) causes › Reply To: Rich (negative long term fuel trim) causes July 5, 2023 at 10:38 am #1025314 Rahul JonesParticipant Try disconnecting sensors like MAF sensor and Throttle Position Sensor then check if the reading changes. Also, you can check if the exhaust fumes reduces or not.