4.0 starting rough when warm

Reply Subscribe

Thread Tools

Search this Thread

Dec 19, 2005 | 04:44 PM

markley34

Thread Starter

New User

Joined: Jun 2005

Posts: 7

Likes: 0

4.0 starting rough when warm

My explorer starts rough when it has been running for any period of time, but when cold it is fine. When I mean rough it revs up and down to the point where it almost stalls or will stall but then if it doesn't stall it will rev back up and down constant until i put the gas down get the truck rpms up for awhile. Any ideas?

Dec 20, 2005 | 07:52 AM

PERFORMANCE RED

Laughing Gas

Joined: Sep 2002

Posts: 759

Likes: 0

Throttle position sensor would be my first guess.

When was the last time you put new plugs, wires, ect... in it? Have you ever given it a good tune up?

How many miles?

Dec 20, 2005 | 08:40 AM

markley34

Thread Starter

New User

Joined: Jun 2005

Posts: 7

Likes: 0

Tune Up

I had a tune up this past fall.

Dec 20, 2005 | 09:25 AM

PERFORMANCE RED

Laughing Gas

Joined: Sep 2002

Posts: 759

Likes: 0

Quote:

Originally Posted by markley34

I had a tune up this past fall.

how many miles does it have on it now?

Dec 20, 2005 | 09:40 AM

mrshorty

Postmaster

Joined: Dec 2001

Posts: 3,742

Likes: 2

From: UT

What year Explorer? Rough warm start is consistent with a leaking fuel pressure regulator diaphragm, but not all Explorers used a fuel pressure regulator. Not sure when Ford started using a returnless system (think it was '97 or '98), but if you have something older, I would check the vacuum line to the FPR for gasoline. Also wouldn't hurt to put a fuel pressure gauge on it to see what the fuel pressure is when it starts rough.