I have Corolla Se Saloon 2003 model. It is on both CNG and Petrol. From last few days, it is missing the usual acceleration (like it starts missing/misfiring) while you are accelerating and hence rpm drops down and suddenly gains back up again giving jerks to the car. The surprising part is that when the car is at rest at mechanic, it acceleration is normal most of the times. This problem only occurs when we are travelling in the car and it suddenly starts missing after a while till end. The jerks/missing is more dominating on CNG while quite less on petrol. I have replaced all 4 ignition coils, spark plugs, air filter, cleaned the MAF sensor but the problem still exist. Any idea what the problem might be?? This problem probably started after the time i got my alternator replaced from an electrician since the last one malfunctioned.