Hi,
New to the site and have an issue which will be somewhat lengthy, but I will post progress and hopefully the solution / resolution for future reference. So here it goes:
1989 Buick ParkAve Ultra w/3800 LN3. Started running rough (at all rpm’*) and SES light was doing the on again / off again thing. OBD1 “blinky” codes were 13, 21, 39 & 41. So I replaced O2 sensor the Camshaft Position Sensor and the Camshaft Position Sensor Interrupter Magnet. Result-SES light no longer comes on, but still have a code 21 (TPS high voltage), and engine runs terrible (no power / acceleration – misses and “coughs” at all rpms) Feels like a plugged CAT Conv. but I replaced less than 3 yrs ago (<20K Mi.) Also has brand new Autolite plugs and wires. So, I feel like I’ve got it narrowed down to just about anything in the secondary ignition system…lol (ie. Ign coil, ICM, MAF Sensor, TPS, ERG, Fuel Pump, etc.)
I’ve borrowed a SnapOn MODIS scanner, but have never used one before and from what reading I’ve done I’m not sure it’* gonna be of much help since car is OBD1.
Any suggestions / advice would be appreciated, I’m gonna hook up scanner tomorrow so I’ll be able to post any useful data if it helps.

Thanks
MW

What have you done to address the TPS code? Did you check the sensor and wiring? That alone can make the car run awful.

Test the throttle position sensor as follows:

https://www.gmforum.com/trouble-shoo...sensor-279319/

I was hoping the MODIS scanner would provide me with some additional info on the TPS, but I've just discovered I am lacking the 12V Lighter Power Accessory for the GM-1 (OBD1) communications adapter. Electrical systems and their diagnostics are definately not my strong suit, but I'll get a multimeter and run the test on TPS if I have to. Debating on whether to spend a few extra bucks on the meter and get one with frequency testing capability in case I need to test MAF sensor. Again I had hoped scanner would check that too.
I thought I might drill some holes in the exhaust pipe on supply side of CAT to see if relieving some backpressure (if CAT is clogged) helps any. I thought this would be better than pulling the O2 sensor.
Thanks guys ! I'll post updates with progress. Any tips / suggestions, question of my sanity is surely welcome.