Couple months ago I bought a 2000 Mustang convertible 3.8L, manual tranny, overall in a very good shape, only 67000 kms on the clock. No issues/problems then.
Few weeks ago I put two mods on the car. First a high flow muffler, which did not create any problems. Later on, I installed a K&N air filter and that was when problems started.

I need to tell that both mods had actually a positive effect on performance, more power and better torque especially at low RPMs. However, shortly after installing the K&N filter, I noticed that when accelerating in lower gears, the engine starts missing/skipping past 2500 or 3000 RPM. It feels like the fuel was momentarily cut off. No problems when cruising or in 5th gear.

I did search the net and as recommended, I cleaned the MAF sensor. It seemed to help a bit but this skipping is still clearly there. I wonder if by letting the engine breathe more freely the fuel management system is somehow confused about fuel delivery.

Any help/comments would be appreciated.

Lumir