Unusual Rough Idle | Ford Explorer Forums - Serious Explorations

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Unusual Rough Idle


July 30, 2012
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Year, Model & Trim Level
1997 Explorer XLT
My explorer has a strange idle problem sometime. When I start my explorer, everything runs fine, in park and in drive/reverse. The problem occurs when I start the car a second time.

After the explorer is started and still in park, the rpm will lower to less than 500 rpm. This starts within seconds after ignition. The engine makes a high/low sound, as if not all pistons are firing (maybe?).
Once in drive, the idling returns to normal and drives fine.

I park my explorer and turn it off to go inside (house, store, gas station). When I go to start the explorer again, the rough idle begins within 10-30 seconds. This idle problem will only occur if the car is turned off for a short period (2-5 minutes). I cannot leave my explorer running because someone could steal it.

Temporary Fix:
If I give the car gas while still in park, this raises the rpm and the strange sound goes away.
If I shift into drive, the sound goes away, but the low rpm remains.

I do know that the upper intake plenum is old and dried out. This is allowing more air into the engine.

You answered your own question. If you have bad intake gaskets this will cause rough idle due to vacuum leaks.

However, I still think something else might also be causing the rough idle. The engine is already warm when I start it the second time, is it possible that a sensor is faulty?