1992 Ford Explorer suddenly running rough at idle RPM especially in gear - any ideas?

4L 6cyl auto transmission 1992 Explorer has always started on first try with no need for accelerator pedal, and ran smooth at about 1000RPM while warming up, around 650 RPM in Park/Neutral/or in gear with brakes on.

Suddenly, it needs gas pedal to stay running without bucking - RPM drops to less than 500, charge guage dips at same time to less than 12 V. Must put it in neutral and give gas at stoplights. Runs fine while moving. This happened immediately after I sprayed Teflon Silicon lubricant in ignition switch, and (more importantly?) left the ignition switch in "On" position without engine running for about 25 minutes. Also new tank of gas 20 miles earlier.

Does something electrical burn up or overheat when you leave it switched on? I have tested it for 5 miles at city speeds but I don't want to get stuck on the Interstate trying to "burn it off" as one friend suggested. Battery seems strong, charge guage returns to 14+ volts when it is running at or above 1000 RPM. THX!

2007-03-06T15:59:41Z

UPDATE --- thanks for your quick replies and good ideas. I now know how to spell "gauge" and how to spell-check :)

Odometer has 85000 miles on it; no service record to determine clogged injectors or other factors. I tried gas-dry and ran it at 65mph for about 20 miles, same. Elec system checked OK by parts place; no corrosion, charging normally. Plug wires are in place.

I should get a real tune-up when I have the money, to cover the plugs and wires theory.

Any advice on pinpointing possible vacuum leak? I moved around hoses listening for a change in sound, but no luck. Thanks you all for reading and those who replied! -- tim

mobile auto repair (mr fix it)2007-03-06T07:03:36Z

Favorite Answer

its going to either be a vacume leal most likley or a spark plug or wire fell off listen for a hiss noise for the vacume leak or ckicking for plug wire voltage is normal as the alternator turn off at low speeds spin speed needs to be 2000 rpm or 800 rpms of the motor

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Anonymous2007-03-06T14:34:23Z

I would suspect the gas as we all know what that story is! I'd add some isopropyl to the tank and see what happens. I don't work on Fords so not quite sure what you have on that year. If TBI, might need cleaning. If TPI, then possibly an injector. Also, a vacuum hose could have come off or leaking. Beyond that, would have to look at it to determine cause.

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Anonymous2007-03-06T14:33:54Z

i got your answer... after checking battery cables for corrosion go to parts store . they will check battery,alternator,,for free...i just replaced alternator in my S10...volt gauge was 7 v at idle and 14 at 1000 rpm and above

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____2007-03-06T14:30:20Z

could be your choke is sticking or your carb is on the fritz need adjusting or your fuel is tainted got hold of some cheap gas

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potato2007-03-06T14:27:15Z

check to see if there was a recall on that model with the ignigtion switch

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