2005 Ford Focus • 98,000 miles

I have a 2005 ford focus, 2.0 duratec, automatic. It has been modified but only after a idle/acceleration/cruising problem developed. I am at this point stumped. When the car idles, it lopes badley and very irratically, sometimes when I cruise it wants to stutter and stall, I have to hit the gas pedal until the transmission shifts down and gets higher revs, then release and go back to cruising, then sometimes when i'm cruising and I go to accelerate to pass or just go faster, it does the same thing. Sitting still at a stop light/stop sign or in traffic, I start to go and same thing except with more popping and back firing. I've replaced exhaust, removed cats, changed airfilter (cold-air intake) changed fuel filter, replaced spark plugs and replaced coil pack on clyinder #1, replaced MAF sensor and nothing helps. With everything mentioned above, it doesn't happen all the time, and not even after doing something specific like putting in gas for example, its very sperattic and inconsistent and extremely anoying as its been happening on and off for about 2 years. I also have code P1633 which is KAM memory voltage too low (i think) how would I fix that? Any and all help/advice would be greatly appreciated as this is my only daily driver and I drive a good distance to work everyday
July 16, 2012.

Modified? How and what was done.


Jul 17, 2012.
Just minor mods. Exhaust, header, cold air intake, and hotter burning spark plugs. All changes were made after the car started having the afore mentioned issues. The header has no cat, both exhaust and header are focuswerks products and designed specifically for my 2005 focus with a 2.0L duratec

Jul 17, 2012.