Hi everyone, this site is proof that good things can happen when you're searching for a solution to an error code! We've been chasing a Code 21 (TPS) on a 1991 Buick Riv, and unless we have a nasty vacuum leak that we've been unable to find, then our best guess is that the MEMCAL is fried. All the wiring is 100% as to the usual (continuity, volts, amps) and based on those tests, the Buick Service Manual Diagnostics said the ECM should be replaced. We did that. Of course we swapped over the EPROM/MEMCAL. The car runs great but the error code remains and is driving us crazy. We're about to install Tuner Pro on a laptop and try that for diagnostics, but does anyone know how to tell if the MEMCAL itself is causing the problem? Thanks!