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Old 11-09-2012, 05:21 AM   #9
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Location: the armpit of TN, Memphis, TN
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You can use the electronic odometer trick to monitor voltage while you drive. There's no odo test function for amps that I know of though. This can be a handy trick for problem diagnosis. Usually the alternators on these cars are tricky, but don't cause high idle issues. You might also have a TB that someone fiddled with the throttle plate stop screw.
Key off, press and hold odo reset button. Turn key on while holding odo reset. The needles will jump, and the odo will read [test], release odo reset button. Now each time you press and release the odo reset button you will scroll through one of 30 test functions. Look for the one that reads [bat 12.2], and expect it to read about -.2v from what you read on the terminals. The odo will remain in test mode until you turn the key off, so simply start the engine, and now you'll be monitoring alternator voltage while you drive.

The TPS replacement, follow this procedure: remove both screws, but hold TPS in place. It will twist under it's own spring towards the air intake. This is what it should look like when you install the new TPS, then you turn it back to line the screw holes up. Some people make the mistake of installing it with the screw holes lined up, then forcing it with the screws to be flush with the TB face. That's how it gets broken. It happens often enough that I always ask about that when problems show up right after TPS repair.

PO171 is our typical DTC that points to a bad PCV vacuum line that causes high idle. However, other vacuum leaks can cause high idle. Have you checked the intake manifold bolts? Also, some people have missed the IAC gasket, and installed a new IAC with 2 gaskets. Ford is known for not using gaskets on some parts- the IAC is one of them, but typically with aluminum intakes, there is a gasket. If you check those intake manifold bolts- tighten from center to outside.

Forgive me if I'm too rudimentary, we sort of assume nobody knows anything until we know better.
Be eclectic.
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