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My 1984 98 just started bogging from 40 t0 50 under a light load, not so much when you jam on it and is a little rough at idle, it's got code's 22 TPS sensor circuit voltage low , and 41 No distributor reference pulses to the EMC at specified engine vacuum . I have an appointment for the 25th this month but was hoping it's something a guy that knows a lot about nothing could tackle, I have the cd and thick electrical book but I am still a green horn and some things just don't compute in my brain. Any help would be appreciated, thanks Brian
Last edited by pgapapa46; Jun 9, 2026 at 06:30 PM.
Unless you're fluent in code reading (CSM goes a long way here- found under driveability section) and comfortable around ECM and components and what they do and when they do it, it's a rabbit hole you may not be able to escape from and you could make things worse. You can't do a half-azz job with it and you can't adjust everything at once. There's a lot of people that have no clue on OBD stuff, even though your car is one of the simplest forms. They start fiddling with stuff they have no clue about and royally screw up stuff.
To check your base timing, you need to put it in "field service mode". Whatever you call it, The ECM has to be taken out of the loop to NOT control timing advance/retard. You do this by first starting car. Then jump the ALDL under the dash terminals A and B (upper two RH terminals) with a wire/paper clip, whatever, set your base timing (20 degrees BTDC), and then take it out of service mode by unplugging the jumper, then turning off the car.
If the engine runs, then a real code 12 is just the reference starting point meaning the ECM is communicating with the system and starts and ends the diagnostic sequence. Otherwise, if the engine won't run, code 12 could be a problem. Typically, it is not an issue.
Here's a quote from an ex-GM tune up tech on code 41 that may help.
Yeah, that EST signal is kind of hard to understand if you're not seeing how it works digitally via a lab scope. Basically once the engine gets past 400 RPM, the ignition module sends a 5v signal to the ECM (pin C at the ECM) to tell the ECM to start managing timing advance. The ECM then starts talking on the EST line (pin A) going to the distributor to phase shift the timing advance and retard (you can see this happening with a lab scope). If the EST signal is working....the ECM manages the timing advance based on PROM info and sensor input. These early carb and F.I. systems required you either grounded the EST line or opened it based on what the info sticker said on the fan shroud to get the base timing correct. If you didn't do this right, you were actually trying to set the ignition timing while the ECM was advancing the timing (ending up in a gutless wonder for engine power).
Code 41: NOTE- You have a VAC on your 5.0L Olds. Not a MAP. Those are on 6 cylinders and others.
Code 22:
Your VAC is located under the little shield plate with 2 little bolts on the passenger side fenderwell.
Thanks very much, I had the old VAC hanging out, put it in and didn't have the code 41 on my last check, I will look into the TPS and see if I can handle it. You were very thorough in your response and I appreciate it. Thanks
