Idle
Surge Quick
Fix - Ten Pin Connectors on EEC-IV engines
Every
owner of a 5.0L EEC-IV controlled engine has probably experienced,
or one day will, the dreaded "idle surge". Ford terms it the
rolling idle, but either way its annoying as hell to watch
the idle stick at 1500, then drop to 700, then float to 1000
and so on. Or perhaps you've just got strange and annoying
EEC gremlins and you're at wits end. Well we've got one other
thing to check out before you roll your car off a clif, the
ten pin connectors.
Always
start by checking the basics: vacuum leaks, throttle position
sensor voltage, resetting idle, and pulling codes.
Once
all these ideas are checked out and crossed off the list,
check the ten-pin connectors on the main harness. These connectors
are notorious for developing loose contacts. Ford even issued
a TSB on some model years, and dealers installed an "extension
harness", thinking perhaps the original harness was too short
causing the large connectors to pull apart. The fix below
It
may be a long shot in solving your problems but its not a
bad idea, and another thing to check off your troubleshooting
list.
The
"ten pin" connectors are these salt and pepper shaker looking things
found at the back of 5.0L engines -between the intake manifold and
firewall. These connectors are notorious for developing poor connections
and causing strange EEC quirks, like idle fluctuations, check engine
lights, and unexplainable diagnostic codes to be triggered. On many
Mustangs there may be a dealer installed extension harnesses, making
it appear as if there are a total of four of these connectors. 
Using
a nail or sharp punch spread the male connectors open just slightly.
This will ensure a complete contact. If you open up the ends too
much use needle nose plier to sneeze the "leafs" back together.