Car Surges with Heavy Throttle

[MountainMan300]

I have a 1998 GT Convertible, 4.6, with a 5 speed manual.

It has started surging under heavy throttle in any gear; the car doesn't have the power that it should, and I can physically feel the car surge when trying to accelerate.

The car drives totally normal otherwise; it's only under acceleration when I give it about 3/4 or more throttle.

Any ideas on what it could be? I'm not super familiar with the 4.6 family of engines.

 

[94IndyPace]

Bad gas, when was the last tune up. Still have cats? Mileage

 

[MountainMan300]

Bad gas, when was the last tune up. Still have cats? Mileage

Fresh gas, not sure when the plugs/coil packs/wires were last replaced (I haven’t had the car very long).

Still has cats but someone chopped the exhaust off after them. Dumps after the third cat on both sides.

Odometer is stuck at around 164k.

 

[94IndyPace]

I would at least change the plugs and fuel filter

 

[ttocs]

Is the CEL on and have we pulled any codes?
pull a plug real quick and see what it looks like and that can tell you a lot