What were your other numbers? What type of fuel are you using? Where's your timing set at?
You probably do have carbon built up because of the way it's been babied. I'm sure the guy who owned it before you probably always used Premium because it's the most expensive and, therefore, the
best.
You may also have clogged injectors. Have you pulled your codes from the computer? Did you do the engine running test? Was your car nice and hot when you got it tested or was the testing station just down the block?
What kind of plugs are you using? Are they gapped according to the emissions sticker?
We need details.
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351W 89 Mustang GT Convertible