So currently my car is running pretty poorly. On acceleration it kind of hesitates on and off. It used to happen on the highway over 60mph but now it's happening all the time. Also the car sounds bad. It has a throaty sound on acceleration (everything is factory so it should be quiet) and at high rpms (5000+) it sounds like there's a plastic bag fluttering around in the engine bay. But it only does this under load, not revving in neutral.

I'm thinking a vacuum leak but would like some ideas on what to look for if anyone has experienced this before. Thanks!

 

I would check all 4 injectors with an engine stethoscope. One stuck open would get you here. Do you smell unburned gas in the exhaust at all?