So I've been having this issue with my s4 and Its very annoying.. The car runs perfectly fine. Idles normal. drives fine. good on gas. but when I try and give It a go It will rev fine until It hits around 3800 rpms. Then It starts revving slow and bucking.

Its weird. You can feel the car fall on Its face and stop moving. then It will skip revv the whole time. and even If I'm cruising just going above 4000 rpm that car starts acting up and doing a slight buck. Anybody ever have this problem?

 

It's a common ailment. Search in the 2nd gen forum and you'll find a lot about the problem.
- Could be as simple as fixing the grounds
- Could be as simple as freeing up the function of the secondary injector actuators.
- Might need to clean your injectors

Like I said a lot of people have had this issue and it has been discussed many time in the 2nd Gen forum.

 

as well as if the car is flooding out alot (probably due to injectors) could be fouling out your plugs. =)

 

you secondary injectors are not opening

now, why is that is different issue.

you need to do ECU diagnostics covered in FSManual

 

yup.. secondaries are not coming online

(at least one of them)

you've got some investigating to do..

 

man i totaly read that wrong i thought he said it wasnt just the 3800 rpm ailment i thought it was more consistant my bad.