Loud muffler. Van Jumps forward in idle and RPM goes up. When the van jumps, the muffler puffs simultaneously and smells.
My car has 150000 miles.
My car has an automatic transmission.
This may be related to a failing catalytic converter or potentially a dirty or failing idle air control valve. The idle air control valve reads the air intake as it enters the motor and relays this information to the computer which makes adjustments to fuel. When this is not working properly, you may experience an intermittent idle problem as you have experienced. This may also cause a rich fuel condition producing a smell of fuel as well.
To avoid any unnecessary repairs, I would recommend having an expert from YourMechanic come to your location to diagnose the smell and noise firsthand. One the issue has been pinpointed, the mechanic can service the catalytic converter or idle air control valve as necessary. Best of luck.
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