90Mustangfan

what causes the rpms to come down slow....it revs up the they come down to 1500 and sits the for 3-4 seconds the comes to idle..what causes it?

Quik

salt and pepper shakers. do a search and youll see i made a reply about it

yzfr6i

It's your Idle Air Control valve. They get clogged with carbon and need to be cleaned out.

Quik

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.

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 is simple enough to perform, and should be done as a preventative measure even if you dont have surging problems.

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.


1. Disconnect the negative battery cable! To open the connectors squeeze the four side clips and pull apart. Do not pry the clips apart as with other connectors. The inner workings reveals ten male and female connectors.





2. 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.



Before reassembly take some spray electrical contact cleaner and clean the male and female connectors. FM