Is this a car that has a distributor? If so, take a peek inside.

One would think that the original wires are due to be changes long ago. I like to pull spark plugs and see what color they are trying to get some idea of the combustion and you also get to check the plug gaps. Note if the wires are originals the plugs might also never have been changed or even pulled.

You are doing better than I am. I have an 86 cavalier that the ignition module died on. When I decided it may be the module, I found a rebuilt distributor on eBay an put that in and it ran well for several weeks and killed that ignition module.

I installed another ignition module and when I drove it, I got about 45 minutes out and another module died.

Some of the things claimed to kill the modules are if a diode goes the ac ripple voltage can kill or on another forum a bad coil was claimed.

No difference in the ac voltage from the cavalier to compared to my 2012 Equinox so I am guessing that is not the issue. New module and coil and car run again but not road tested as it needs suspension work. End of issue still pending.

Note I had an auto scanner that I managed to misplace used on my 92 Astro van and it told a bit more compared to what the code looks up said. I don't know if autozone has free rentals on them or not.

Failing EGR controls can also cause odd performance issues.

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84 300D, 82 Volvo 244Gl Diesel