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Have you check out your IAC motor? My first guess is a vacuum leak though. I assume no trouble codes?

 

This morning we was able to get a code 43 out of it, first time that has shown up in scans.

 

Ok well lets start there and work our way from there. A code 43 indicates a problem with you ESC system. What it should do Is tell the ECM to retard the timing in the presents of a knock. What this code is saying is that you ECM has detected that your ESC module has told the ECM that it is constantly knocking regardless of how far the ECM pulls back the timing. What we need to do is first confirm what signal the ESC module sending to the ECM? Is it sending the 8 or 10V everything ok no knock present signal or 0V telling the ECM to retard the timing? If its 0V we have a problem with either the ESC module, the knock sensor or the associated wiring. If its 8 or 10V we need to confirm that the signal wire is not broken and has a good connection to the ECM. Most likely we will find some sort of problem but if not we need to determine whats causing it to knock. One step at a time though.

 

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Oh well thats probably because your ignition control module is bad. It drives the tach and all that. Also as far as the ESC i forgot the 90-91s had the integrated ESC module. Unfortunetly i dont have a schematic for those to see how there set up so i cant say much. Ide suspect a broken wire, bad connection, or bad knock sensor. Start with the ignition control module though as the RPM has alot to do with the ECM control of spark and fuel. If the ECM dosnt know what RPM it is it will never work right.

 

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