hesitation at 1/4 throttle less from a dead stop
 

I have a hesitation when acellerating from a dead stop only. It happens when i give it about a 1/4 throttle, and occurs only for about 5 seconds, less even, until i hit about just under 1500 rpms or 5-10mph, then it goes away, doesnt happen when im crusing, nothing. Also, i get this hesitation at idle very lightly, i dont think its a misfire, this hesitation I cant feel, i can hear it though, Its spirratic as well, sometimes it will do this, others it wont. I replaced the F/F today, and checked my fuel pressure at the rail after i replaced the filter, at my rail I have about 34psi at idle (750 rpms), and the specs say i should have between 37-41psi, now could this be the cause, only 3psi lower??? I also checked my coil pack as well, thats fine, the resistance between all coils was 11. I only have the same SES code that ive been having, the Open oxygen sensor circuit one, but i dont think this is related.

I would recommend replacing that o2. Not sure I've ever heard of it causing hesitation, but it does play a big role in A/F mix, which could cause some hesitation.

replaced the 02, with an ACDelco one.

well if you're getting that code, i would check the wiring that goes to the o2 sensor. I'm just thinking that it could have alot to do with this. I had this same problem on my old cutlass with the 3300. Same exact problem.

I would follow the wires as far as possible and see if they coulda gotten shorted somewhere.

How's the gas mileage. Right now, I'm thinking about your fuel pressure. Test it with the vacuum line pulled off the fuel pressure regulator on the fuel rail.

what would i be looking for if I did this? Gas mileage seems ok.

Well above 40 psi. And if there is fuel in the vacuum line you need a new FPR. Run the engine for a few minutes, then pull the line to see if there is any fuel in it.

Ill try this later today and will let you all know what happens.

Ok, pulled the FPR vacuum line, the pressure rose to like 40-45 psi then i plugged it back on there, so I think the FPR is fine, i want to focus on the O2 circuit open code ive been getting, I hope its not my PCM thats fried, maybe the code has everything to do with the stumble at idle and low accel

You did disconnect the battery after you installed a new O2 and did all that work? I find disconnecting it, and turning the key on to keep all circuits open works well because it clears the ECM of all trouble codes and leaves it fresh. Leave it for like 30 mins, and see how it works after that?