Rough running Ranger

What do you have for codes
check for vacuum leaks
check intake manifold gasket

Have the engine idling and listen for a hissing noise and try to follow it to it's source. If you have a PO171 and PO174, we see these a lot and they are usually caused by a severe vacuum leak. It's common for the large rubber connectors to suck a hole right through them.

Yes, that is possible. Try some MAF cleaner and see if it makes any difference. If it makes any difference at all, replace the sensor but your going to need a scan tool to monitor the adaptives.

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GOOD LUCK

LIGHT TRUCK: 1997 AEROSTAR, RANGER
TSB
98-6-8 ROUGH IDLE - MALFUNCTION INDICATOR LAMP (MIL) ILLUMINATED - DIAGNOSTIC TROUBLE CODES (DTCS) P0171, P0174, P1131 AND/OR P1151 STORED IN MEMORY - 4.0L ENGINES ONLY
STALL - DURING IDLE - MALFUNCTION INDICATOR LAMP (MIL) ILLUMINATED - DIAGNOSTIC TROUBLE CODES (DTCS) P0171, P0174, P1131 AND/OR P1151 STORED IN MEMORY - 4.0L ENGINES ONLY
LAMP - MALFUNCTION INDICATOR LAMP (MIL) ILLUMINATED - DIAGNOSTIC TROUBLE CODES (DTCS) P0171, P0174, P1131 AND/OR P1151 STORED IN MEMORY - 4.0L ENGINES ONLY

This TSB article is being republished in its entirety to correct the part number listed, revise the Service Procedure, and add Aerostar.

ISSUE:
A rough idle, stalling at an idle and/or Diagnostic Trouble Codes (DTCs) P0171, P0174, P1131, and/or P1151 may be stored in memory on some vehicles with a 4.0L engine. This may be caused by the gasket located between the fuel rail and lower intake manifold losing its compressive loading and becoming drawn into the intake manifold runners resulting in a vacuum leak.

ACTION:
Replace the fuel rail-to-intake manifold paper gasket with a revised gasket. Refer to the following Service Procedure and the 1997 Ranger or Aerostar Service Manual for removal and replacement procedures.

SERVICE PROCEDURE

Remove the upper intake manifold and inspect the O-ring style gaskets on the mounting surface of the upper intake manifold. If the gasket bead is above the intake surface and is not torn, do not disturb the gasket. If any of the O-ring gaskets are torn or do not protrude beyond the mounting surface of the upper intake manifold, the gasket should be replaced.
Remove six (6) studs and lift off fuel rail manifold and paper gasket.
Inspect all holes in the lower intake manifold to make sure there is no debris.
Replace the Gasket (F8PZ-9E436-AA) (bright green paper and blue bead) and set the fuel rail manifold on the gasket. No paper gasket is needed on the top side of the fuel rail manifold.
Lubricate the lower portion of the stud bolts with a light grade oil such as 5W30 and torque the bolts to 14 ±2 N-m (10 ±1.5 lb-ft) using the torque sequence shown in Figure
The upper intake manifold should be installed and the nuts torqued to 25 N-m (18.5 lb-ft) using the torque sequence shown in Figure 1.
Start and warm the engine.
Allow the engine to cool and retorque all of the nuts to 25 N-m (18.5 lb-ft) using the sequence shown in Figure