Hi All - I have a buick Century V6 (1988) and it starts to spit and sputter and sometimes backfire when it warms up, and it is nearly impossible to get the thing to run up off idle when that is happening.

I did some checking, and noticed that the TPS reference voltage is 5V when key on engine off, but once I start the car that voltage jumps up to 6V.

Also, when it spits and sputters that reference voltage seems to bounce (typically between 5V and 7V), which also causes the TPS signal to bounce as well.

Any ideas on if this is a PCM/computer swap issue or if this sounds more like something electrical? Anything else I can check? Also, sometimes it runs just fine, and sometimes it will spit/sputter. I have seen it go between spitting/sputtering/no power and running fine multiple times on the same trip (ie without stalling and having to restart).

Little background, I have replaced the fuel filter (within last 30 days) and fuel pressure is 40psi at key on/engine off, and idles about 32PSI. When car starts to spit and sputter, the fuel pressure goes up to 34PSI, and will drop back to 32 when it starts to idle smooth again.

Was planning to check reference voltages for the EGR and MAF as well just to see if they exhibit similar issues. Doesn't seem to have any of these issues/symptoms while its warming up, but seems like once it gets to closed loop, things start to go haywire.

Edit: Just went out with car cold, checked TPS reference voltage key on and it was 4.85V. Started the car and let it idle (didn't move throttle at all) and watched the reference voltage slowly climb. Once the reference voltage hits 6V (+/-0.05V) the car starts to stumble and stall. Sometimes the reference voltage drops below that range and it recovers, but eventually it increases. I then check the reference voltage and it is back at the 5V area, and restart the car and the same creeping TPS reference voltage happens.


Appreciate any input/advice.

Thanks.