[Blue Bowtie]

They all use the same 5VDC reference supply in the wire harness, and it's not uncommon to find connection problems on these Buick 231s. The IAC only has two stepper drive signals from the PCM and does not use the local ground nor the 5VDC reference supply.

The kicker is that the CTS and TPS are a bit more forgiving, with perhaps a couple of seconds of tolerance by the PCM for signals out of range before an error code is set. The PCM watches the MAF inpuf very closely, however, with as little as 600mS for an out-of-tolerance signal before an error code is set. Thus, a 5VDC supply problem will almost certainly be picked up as a MAF error and may not be picked up as a TPS/CTS error.