My 91 f-150 4.9L has an erratic idle. This happened at about 80,000. I disconnected the vacuum hose to the fuel pressure regulater and this helps. I've been driving with this disconnected for a while. can some let me know what to do.

 

Have you tried disconnecting the battery yet? Alot of the newer EFI trucks idles are set by the computer. Try disconnecting the battery for at least 20 min, then re-connect and let it run for about 5-10 minutes before driving. Hope this helps.

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