Voltage controlled thru opamp playing up?

[diagnostix]

Hi everyone, we have a project which has the following problem. We are reducing a variable voltage on a cars sensor which ranges from 0-5v. We are using a PIC18 and MCP6004 opamp as a buffer with 56k 33n 56k 4.7n RC filters in and out. The problems we are having are:

1. At around 1.0v - 1.5v we are getting a small surge, and variable voltage which is like a pulsating surge. Beyond this voltage all seems to work fine.

2. At 0.9v instead of reducing the voltage out, what seems to be happening is the voltage in rises instead?

Has anybody an idea as to why this is, and perhaps a solution? We thought maybe it's opamp oscillation, or a feed back issue?

Hope someone can help me.

Thanks

Mike

[pebe]

We need more details. Can you supply a circuit of your set-up?

[diagnostix]

Hi, we have removed the PIC today and jumped voltage in - out pins and the opamp circuit works perfect, so maybe the PIC is the problem, we are using PIC18 and pwm at 1250Hz.