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Q: Engine is running horrible with stalling and noises under load.

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recently it suddenly started running really badly. I'll list my observations.

-Loud, low pitched roar as the engine speed increases -rough idle, revs jumping all over the place, sometimes stalling, especially if air con is on. -metallic (tappet) noise when under load, higher engine vibration, worse than usual acceleration. -Often misfires, especially in the first minutes of operation.

This group of symptons used to appear periodically in the past, but would eventually disappear a few minutes after appearing, as suddenly as they appeared. I'm more worried because it has been 3 days with these conditions, and it has not improved. I'd really like to get to the bottom of this because it doesnt seem like the usual wear and tear that an old engine like mine displays, due to the sudden onset of the bad running, and that the issue usually resolved itself in a matter of minutes. Engine is a 4A-F (carbed) with 324,000km on it.

My car has 200000 miles.
My car has a manual transmission.

Hi and thanks for contacting Your Mechanic. As for the engine misfiring and having an issue with the rough idle, there could be a vacuum leak on the engine. Check all of the vacuum hoses and the intake to see if its sealed. Also, check the brake booster to see if its leaking vacuum. For the loud noise, there could be an exhaust leak or the engine could have a worn bearing in the engine. There could be a rod bearing that has too much clearance and is causing the tapping noise under a load. Also the engine could be vibrating due to an ignition problem. Check the distributor, plug wires, and spark plugs for corrosion deposits and heat burns. Check your carburetor for any adjustments that could be out. If you have traveled to a higher or lower evaluation, then the carburetor will need to be adjusted for the altitude. This will help with the stalling of the vehicle. If you need further assistance with your vehicle, then seek out a professional, such as one from Your Mechanic, to help you with your engine misfiring having a tapping noise under heavy acceleration.

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