My 87 used to do that under either of two conditions: first, a mis-adjusted TPS, and second, issues with connectors.
As a first step, I'd recommend unplugging and replugging every single connector you can find in the engine compartment. Those Renix systems seem to be very sensitive to slight resistance in connections. I know it sounds silly, but it often seems to help.
Second, check the TPS settings. Search here and I think you'll find the procedure. I post my paraphrase of the service bulletin instructions here periodically, but I'm away from home and don't have it handy to copy and paste.