The truck has been running flawlessly but tonight after leaving my parked location I started it up and the engine immediately revved up to 3000 rpms with a slight surging. I stopped and restarted the engine several times but the condition didn't change. Any idea as to the cause?

 

You might get better responses if you told us what year and engine you had, type of transmission may also help.

 

I guess I assumed that since I'm in the 4.0 area that I was implying I had that engine. It is that and has an automatic transmission. Thanks for your prompt.
It is also a 4x4

 

Now is it a 4.0 OHV or a 4.0 SOHC ?

And still need the year.

 

It is a 2006. I haven't had the vehicle that long and I don't know how to tell the difference between the two types of engine. And since it was un-drivable I had to leave it where it was parked. On the plastic cover over the engine it just says 4.0 as I recall. Where would I find out which type it is?

 

It's an SOHC

 

Odometer (miles on truck) can also help.
It's hard to assess a problem but the following suggestion is a visual you can easily do.
Look under the 4.0L S.O.H.C. cover (3 hex-head screws) and see if the throttle cable + TPS are secure.
The TPS is plastic bodied and can break.

 

More information:
I drove to the location where it is parked. With, as I recall, both feet on the floor I started the engine. It started and ran normally. So I thought I would drive it home. I put my foot on the brake pedal and the engine immediately revved back up to about 3000 rpms. After 10 or so seconds l it dropped back down to about 2000. But the I depressed the brake pedal again and it went right back up to 3000. Seems like a good clue but to what I don't know. The vehicle has 103,000 miles on it

 

I looked at both the throttle cable and what I suspect is the throttle position sensor. The TPS was black plastic and on the opposite side of the airway from the throttle cable. Both looked secure and the sensor plastic looked unblemished and appeared to have no cracks.
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What we have here is a failure to communicate, as Strother Martin said to the prisoners in Cool Hand Luke. I replied to an earlier post and that reply, benign as it was is being segregated by the moderator

 

​​​​The throttle cable and TPS are secure

 

A surge to 3,000rpm sounds like you're letting air into the intake system.
I am not 100% certain on power brake construction details but you may be flexing a cracked rubber diaphragm in the booster thus letting air in.
This air goes through the booster's vacuum line and the revs go up.

Try starting the engine "with both feet on the floor" (as above) and pulse the brake pedal to see if you can make the revs go screwy?
I'm thinking this would a clearer diagnosis of a bad booster.

 

I did notice yesterday that a lighter touch on the brake pedal when the rpms had dropped resulted in the rpms increasing but only firm pressure took them back up to 3000. But if there is a cracked diaphragm I wonder why it takes awhile for the engine to slow back down. Maybe the air passing through the suspected crack keeps the crack open and prevents,at least for a little while, the hole from closing to its normal position.

 

Disconnect the brake booster vacuum line, plug it so air doesn't enter the engine and see what happens when you start the car.

 

I write this in a state of embarrassment. Before the incident in question I had parked the Ranger at a laundromat where I was washing a bedspread. While killing time I went out to the truck and was about to get in when I noticed that the Weather Tech floor mat had a **** load of debris on it. So I removed it to dump the debris but when replacing it I put it under the brake pedal but over the gas pedal. It is very thin but also very stiff. So when I stepped on the brake at the same time it depressed the gas pedal. Problem solved but I feel like an idiot.

 

Remember the VW 411 and 412?
With more than one pair of shoes I had -with my right foot all the way against the "trannie hump"- I'd also hit the brake pedal.

 

Anyone that has worked on vehicles has done something similar, don't beat yourself up to bad.

Glad it was a simple fix.