You might be chasing your tail. Have someone hold 700 rpm while you check for vacuum. Low vacuum is a symptom of low idle, if you have 18 ish inches of vac then your system is ok.

Buy a bottle of redline fuel system cleaner and try that with an Italian tune up.

If you already did the ignition tune up with quality parts, and the vacuum system holds ok, the next thing to change the fuel injectors.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2