2003 Ford Sport Trac 4WD 4.0L V6 -- Idle, running/stalling problem

[Charles Ward]

I have a 2003 Ford Sport Track with only 120k miles, that I recently purchased. It has a car starter installed and the first thing I noticed, when the car starts and I inadvertently hit the break before putting the key in. I have to start it again. It starts, revs up to about 1500 RPM and then goes right back to 0 and dies. Only way to fix it is either wait for a few minutes to start it again or rev the engine up for about 10 seconds. During that time, it runs very rough. Then it smooths out and runs as expected.

I have also found that the engine occasionally will surge, almost die and then surge again while idling. If I rev the engine up to about 3000 RPM, the engine shakes about every half second, like it is missing.

I have checked the vacuum and changed the elbow hose that commonly fails. I have replaced the spark plugs and checked for the infamous intake gasket leak.

I have cleaned the MAP sensor, the intake valve and replaced the air filter.

There are no error codes. One minute it runs like a top. Then sometimes it will stall and sputter. it will idle as expected, then later idle rough again.

Any have any other suggestions?

 

[swshawaii]

Sounds like a fuel issue. Have you scanned for stored trouble codes regardless if there's a check engine light or not?
Fuel filter replaced? At 120k, my bet is on an intermittent or faulty fuel pump. BTW, there is a rev limiter that kicks in around 3000 RPM that prevents grenading the engine without a load in park or neutral. On some models there is also a speed limiter around 90-100 MPH. Before throwing more parts at it call around, most larger auto parts stores check for DTC's as a free service. If any codes, write the NUMBERS down and post them.

EDIT- Sorry, missed that you have NO error codes. Check fuel pressure anyway.

 

[koda2000]

Also, the engine rev'ing to 1500 RPM immediately on start is normal for the SOHC V6 is normal. It's known as the SOHC starting flare and is done to get oil pressure into the chain tensioners ASAP.

 

[gtyates]

Also could be the idle air control valve, known as IAC. That would explain the idle dropping to 0 and truck dying.

 

[Charles Ward]

I checked the IAC and cleaned it. Seems to be running better but still has the strange "miss" when reving to about 2500 rpm or so. If I maintain that RPM, the engine shakes about every half second, like it is missing.

 

[swshawaii]

In addition to the mentioned IAC and MAF sensor cleaning, the throttle body should also be serviced. Highly recommend using CRC throttle body cleaner instead of harsh carburetor cleaner. Removal of the throttle body is not necessary, and the four self tapping screws are very easy to strip in the plastic intake. Use cord or a tie wrap to hold the throttle butterfly plate wide open, and a stiff toothbrush with paper towels to clean. Concentrate on the bottom of the plate where it contacts the throttle body. If you've never cleaned it, you'll be amazed at the amount of carbon and varnish buildup that's removed, and how much better your vehicle idles and runs.

Untitled Document

 

[koda2000]

You might have a leaking fuel injector. When you replaced the old spark plugs was any one more black than the others? If a fuel injector leaks it can cause hard starting and a miss while running. Also check to make sure you didn't crack a spark plug insulator when you installed the new plugs.

Tip 1: Misting water from a spray bottle around the spark plugs and wires at night can be helpful in locating cracked insulators or bad plug wires. If you see any arcing you know you have a problem.

Tip 2: When you turn your engine off, fuel pressure remains in the fuel line for at least a few hours. If you have an injector that's leaking it could flood one cylinder and foul the spark plug. Use a fuel pressure gauge attached to the fuel rail to see how long the system is holding pressure once the engine is turned off.

You may find some useful information at the following link.
How to: - Ford Explorer Ranger Fuel pressure test procedure

 

[cadman]

Did you 'smoke' your engine to see if you had any vacuum leaks?