Hi Robert,
I'm sorry but I'm having a hard time understanding you. I like to help you but it's just hard when you don't even answer my questions. Now you say it's close to being PID? What exactly is it that doesn't work?

If the motor isn't "stiff" enough you need to tune the PID parameters, I see you have Kp, Ki & Kd exactly as in my example code - which is just that - an example. You need to change them to suit your application.

Also, you could as well changed your code to read pid_Out_Clamp = 640 instead of hardcoding 640 into the incPID routine. In any case if you only have 10bits of PWM resolution why allow the output to swing to +/-640 which is 11bits?

Another thing I notice is that you preset TMR 0 with the value 237, but you do that only at the beginning of the program, so it will go from 237->256, cause an interrupt, then it will start from 0 again. With the pescaler at 1:256 that will be an interrupt rate of 38Hz which might be a bit slow. You need to preset TMR0 again in your ISR.

You can change this:
Code:
advalue = y
pid_Error = Setpoint - ADValue
To simply read
Code:
pid_Error = Setpoint - y
It won't work any better but a little faster and it'll save you a byte or two ;-)

And, try removing the LCDOut statements as a test and see what impact that has on it. Do you have an oscilloscope? Connect it to a pin, set the pin high the first thing you do in the ISR and low again before returning - then you can see if you have the correct interrupt frequency.