Idle bogs out when shifted into park

[Livewire322]

I have a 2001 explorer sport with ~75000 miles.
Recently it has developed a problem that has me stumped.
The idle is pretty rough and sits around 600 rpm while in drive after the engine warms up. When I shift the vehicle from drive into park the idle drops and the vehicle stalls out (sometimes) or will rapidly cycle between nearly zero and 500 rpm several times and then finally settles out around 500rpm.

When I start the heater while the car is in drive the idle drops off and spikes back up repeatedly until I depress the throttle.

I cleaned out the IAC and replaced the air filter but it doesn't seem like its made a difference.

I was wondering if anyone has had this problem and what the remedy was.

 

[manimal]

Same issue here. It was a lot worse before I changed spark plugs and wires, but it still occurs.

I have also cleaned and checked IAC valve and the inlet filter, checked that EGR valve is not stuck open, blocked off all manifold tees to check for vacuum leaks, and most other normal tune up steps you can think of.

When in gear or moving, runs great and has lots of power. Sits at a light in gear with no idle issues, but as soon as you drop it into Park or neutral, the idle slowly degrades. It has never died but it sometimes seems like it may.

I've noticed two things:

- Engine often whistles under mild load or St idle, when vacuum would be high. I suspect the upper intake or fuel rail gaskets are leaking and I plan to replace them.

If there is a vacuum leak at the manifolds, being in gear and driving the torque converter may be enough load to soak up the additional air inlet not metered by the MAF

- I use the BAFX OBDII reader with Torque Pro on my phone and it sometimes shows a pending O2 sensor code, but the code is never set active, so a CEL never gets set by the ECU. That doesn't mean that the O2 isn't bad, so I'm going to graph it's output over a couple trips and see if anything is erratic.

The problem only occurs when hot, and this would be when vacuum leaks in the intake may present, due to clearances between mating surfaces changing via heat, as well as when the ECU goes into closed loop and begins monitoring the O2 sensor.

 

[swshawaii]

OP, check the PCV elbow. Does not always throw a CEL or trouble codes.
Very common failure with 2001-03 two-door Sports and 2001-05 Sport Tracs.

http://www.explorerforum.com/forums/showthread.php?t=314670

 

[Livewire322]

OP, check the PCV elbow. Does not always throw a CEL or trouble codes.
Very common failure with 2001-03 two-door Sports and 2001-05 Sport Tracs.

http://www.explorerforum.com/forums/showthread.php?t=314670

I have already replaced one of the elbows and it hasn't made a difference. Couldn't figure out how to get at the back one without pulling the coil pack etc for access.

 

[swshawaii]

Agree with manimal, scan for stored trouble codes, check engine light or not.
Very extensive and detailed, but the best tech info on EF for the 4.0 SOHC. GL

2000StreetRod's Helpful thread list
https://www.explorerforum.com/forums/showthread.php?t=263665

 

[Livewire322]

A bit of a side question, what spark plugs are equivalent to the MOTORCRAFT AGRF 22P's that are in it. The local part store gave me NGK TR55GP, but those guys have a nack for giving a guy the wrong parts.

Also, does anyone think that the PCV valve could be causing these issues?

 

[swshawaii]

MOTORCRAFT SP500 {#AGSF22FM, AGSF22FMF6, AGSF22PP} Finewire Platinum
2001 FORD EXPLORER 4.0L V6 Spark Plug | RockAuto

agrf 22p-agrf 22p Spark Plug

 

[Livewire322]

Thanks, didn't think to check rock auto!

 

[Livewire322]

Alright, I replaced the entire hose that was mentioned above as well as the PCV valve but it did not solve my problems.
Does anyone have any other ideas as to what might be going wrong?

I'm thinking of taking my truck to the stealership and having it repaired.

 

[koda2000]

Just guess and I've never actually heard of it happening, but I'm wondering if it has something to do with the torque converter, transmission pump or perhaps a trans solenoid. Maybe when you put it in PARK the trans is keeping the line pressure up when it shouldn't be?