91 crx hf sputters???

I just purchase a 91 crx hf for a tuner car. The motor has 188K on it and starts really nice. The problem im having is its sputtering on most of the gears, especially around 50-60mph. I tuned it up, changed plugs, plug wires, fuel filter, valve lash, timed it too!!! The check engine light doesnt come on. When fixing the idle i noticed it has a 1.6 engine intake on it instead of the 1.5 intake, so they must of swapped it, the engine is still the d15b6 motor. The rpm's dont flucuate. It drives nice until it sputters and it shakes the whole car, its almost like its not getting enough fuel but who knows, i put 3 bottles of fuel injector cleaner on the last 3 fuel ups. When I changed the spark plugs the first plug on the left as if your looking at the valve cover from the bumper had dry black stuff on it, the other 3 were perfect. I looked it up and it said that may of been because of the air fuel mixture? Could this be the problem? I know the timing was off though. This problem has really been bugging me. Can anyone help???

thanks,
egg

hey, it might be the computer. cause it still might be for the old fuel injection. but i ve never herd of some onedoin that swap

hey, it might be the computer. cause it still might be for the old fuel injection. but i ve never herd of some onedoin that swap

the only swap that they must of did was take the old 1.5 intake manifold off and put a 1.6 intake manifold on it, would that matter???