Hesitating, misfiring, running horrible N* tip..
FYI - last year my 94 STS starting running bad, hesitating and misfiring out of no were, I replaced everything: PCM, plugs, wires, O2 sensors, oil & filter, air filter etc..... Nothing I did helped!!
My mechanic scanned it and came up with nothing useful. He did suggest to try replacing the fuel pressure regulator. As i was beginning to dismantle the top of the intake to get to the regulator I found my fuel injector harness had melted on the top of the trans housing causing two injector wires to short against the trans (ground). I repaired the melted wire harness and tie wrapped it up away from the trans.
The Car has been running perfect ever since.
If you are expierincing these simptoms Check your injector harness........
Re: Hesitating, misfiring, running horrible N* tip..
Vaccuum leaks in and around the intake, leaking injectors and fuel pressure regulator can also be culprits of rough starts, refer to other posts in this section for more detailed info on troubleshooting and fixing...