Backfires when...

[BFlat]

... I let off the gas. Nothing major. What to check? TT 91 octane chip. I have a Scanmaster. Thanks

 

['87 Turbo "T"]

Not enough info to give ya an answer. Folks may have some ideas. Without more data they’ll all be just guesses.

How was car running? Speed? Fuel pressure? TPS? Etc.

Post Scanmaster numbers when it happened.

 

[SCOOBY DOO]

You could also post the SM numbers with the engine fully warmed up in Park.