The following is from the Ford TSP on P1519:

DTCs P1518, P1537 and P1538 indicate IMRC may be stuck open. DTCs P1512, P1513 and P1519 indicate IMRC may be stuck closed. DTCs P1516 and P1517 indicate IMRC input error. DTC P1520 indicates IMRC control circuit malfunction.

Possible causes:
-- Cables improperly routed (binding) or seized.
-- Damaged/disconnected IMRC housing return springs.
-- Lever/shaft return stop obstructed/bent.
-- Lever/shaft wide open stop obstructed/bent.
-- IMRC lever/shaft stick/bind or disconnected.
-- IMRC actuator cable/gears seized.

* View cable routing. Make sure cables are not binding or improperly routed. For vacuum operated IMRC systems, make sure sensor linkage is attached and secure. Also, make sure IMRC sensor harness connectors are attached to the proper bank. They are interchangeable. If necessary, use a breakout box to pin out the harness connectors to the corresponding electronic EC pin. With engine off or at idle, cable core wire at IMRC housing attachment should have slack and lever should contact Closed Plate Stop Screw.

* Manually open and close IMRC plates at intake manifold, feel for sticking/binding.

NOTE:
IMRC return spring is strong. Make sure return springs operate properly and plates open and close fully.


The following is also from the Ford TSP:

The air induction system improves engine performance by using the intake manifold runner control (IMRC) assemblies as follows:

* The intake manifold (9424) has two runners per cylinder, feeding each of the intake ports in the cylinder heads (6049).

* The IMRC is integral to the lower intake manifold. The assemblies are located between the upper intake manifold and cylinder heads, providing two air passages for each cylinder.

* One air passage is always available to direct throttle input and the other passage switches from closed to open by means of a valve plate, the intake manifold runner control actuator and cables.

-- Below 2800 rpm, this valve plate is closed to improve low speed and cold engine performance.

-- Above 3500 rpm, this valve plate opens to improve high speed engine performance.

The valve plates are opened and closed by the electric actuator and cable assembly, which is controlled by the powertrain control module (PCM) (12A650).

Here's some more links
Link1

Link2

1996 2.5LT V6 Contour ATX My Tour+help/info pics E0 rims, Gutted Pre-Cats,CTA Custom Exhaust & Intake, Diablo Chip.