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Ford F-150 Rough Idle, Stalling

Q. I have an 1988 Ford F-150 with a 5.0 liter EFI engine and manual transmission. I had a really bad vacuum leak in the brake power booster. I replaced it then another vacuum leak popped up in the upper intake manifold gasket. I just replaced that now the engine has good vacuum, but once it has warmed up it does not want to idle right.

Ford F-150 Rough Idle, Stalling

Sometimes it idles at 750 rpm for a few minutes and then drops to 500 rpm and the computer will try to get the idle back up with mixed results. It will either stall or rev up to 700 rpm and drop down to 500 rpm and back up and down, but will eventually stall.

I disconnected the battery when I replaced the upper manifold gasket, could the computer just be trying to relearn the idle. It runs fine when I drive it has no hesitation, but when I go to down shift the engine speed drops very quickly so I have to heal toe brake to keep rpm up or else it may stall. It also stalls at stops some times.


A. The adjustment or learning period is usually about ten miles of driving. If you have driven this distance and it still has the rolling idle, then we have to look somewhere else.

You will need to go over your work and check vacuum lines. Make sure you have them all connected and that they are connected properly. There should be a vacuum hose routing diagram under the hood., usually on the radiator support.

Then check the throttle linkage. Make sure there is nothing broken, missing or misadjusted. Check the EGR for proper operation, it has to be fully closed at idle. Check all the electrical connectors to make sure they are properly connected and securely locked.

Then you need to check the Air Flow Meter, Coolant Temperature sensor and I would double check the intake manifold bolts. They need to be retightened after the engine has reached operating temperature.

Have you checked the computer for codes? That should be the second thing to do. The first is checking the fuses with a meter or test light to make sure they are good.

Additional Information provided courtesy of AllDATA

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