1988 Buick Century 6 cyl Automatic 80000 miles
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My car recently started jerking when i reached 35. so, hearing the praise about diagnostics, I bought one from the local store and it told me code 43 EST or ESC issues.... So I went back the local store and I was told to replace the Ignition Control Module. I did and it seemed to fix the problem and then on a longer drive the car started jerking at 35 again although not as bad. So again the diagnostic and still code 43.

Did the clerk rob me or what?

Any help from a more experienced individual would be appreciated.

Check the knock sensor. If you have an integrated knock sensor, there is no esc module.

The knock sensor should be located on the firewall side of the engine, below the exhaust manifold, screwed into the engine block. One wire connector, wire color should be dark blue with a white stripe. Take the wiring connector loose, turn on the key, see if there is any voltage on the wire, there should be?