[V8] V8 suddenly running like a coffee grinder above 1700 rpm

[Shiv]

The ECU uses the coolant temperature sensor to monitor
engine coolant temperature as well as the rate of
change in coolant temperature.  This information is
sent to the ECU, in order to determine the air/fuel
mixture required to make the car run at a given
temperature.  Your car may be running like crap
because the ECU is getting a bad temperature reading
from the sensor.  The wrong signal is always being
given.  Your car isn't operating correctly in cold or
normal temperatures because the ECU doesnt know the
temperature of the coolant anymore...it has no idea
what kind of fuel / air mixture needed until that
sensor is replaced....IF that is infact your problem. 
Remember, the fuel pressure regulator can also be at
fault.

Good luck!

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