Im new to thirdgen but I've read plenty of threads that have helped a lot on other problems. So here's my problem my 89 2.8 firebird mpfi will idle fine cold but when I give it throttle it spits and sputters. When it warms up it runs good besides initial throttle response. I've replaced MAF and relay, pickup, rotor cap, dist cap, ignition coil, plugs and wires, TPS, IAC, EGR, o2, injectors, and even ECM, still with no help. I've got no vacuum leaks and my fuel pressure is perfect. Also when I set the timing to 10 degrees it doesn't run right at all I have to set it to around 14ish for it to run.Someone please help me!!!

 

When you checked the timing, are you sure you disabled the ECM advance? You have to do that to keep the ECM from complicating things. It's described here:
https://www.thirdgen.org/settingtiming

If you check timing when the ECM advance hasn't been locked out, then the total timing will be something like 18 degrees or more. Checking for this would be one way to confirm that you did the base timing correctly.

 

Yeah I have unhooked it. That 14ish is what my base timing is, when it advances it's way off the plate. Like the notch on the balancer is directly underneath the water pump.

 

Has it always had this problem since you owned the car?

Does it ever backfire? That might suggest a fueling problem vs ignition/timing.
You mentioned the fuel pressure is perfect - does it respond to manifold pressure? When you open the throttle, manifold pressure will change and the fuel pressure should do the same in proportion (the fuel pressure regulator is connected to manifold vacuum for this reason).

Problems with cold running can sometimes be related to the coolant temperature sensor, but I don't think that would explain why it has a particular problem with throttle response. So I think this is probably not your problem. You can test a CTS by measuring it's resistance with a multimeter. There's probably charts somewhere showing what resistance it should have for a given temperature. The chart I have is for a Fiero so I don't know if it's the same. But at least on the Fiero, 20F is 13,500ohms, 40F is 7500ohms, 70F is 3400ohms.

It seems strange that it runs so badly at spec ignition timing, and needs excess advance just to be decent. I can't think of why that would happen if the timing is where it appears to be. The lack of throttle response would also be consistent with being retarded.
So I'm wondering if the timing mark could be inaccurate.. maybe the balancer has shifted. It might be worth trying to find TDC and see if it matches up with the timing mark.
A worse possibility - maybe the timing chain has jumped.