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John Mc
John Mc, Ford Technician
Category: Ford
Satisfied Customers: 6238
Experience:  19 years Ford Lincoln Mercury experience
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2002 ford ranger: stalling..check engine light comes..throttle body

Customer Question

My 2002 ford ranger with a 4.0 litre SOHC(75k miles, engine is solid) is burning rich and the RPM's are fluctuating and some times stalling out.

When the check engine light is on, the truck seems to run good. When I disconnect the positive cable to the battery and turn the check engine light off, the truck starts to run bad again. Then the check engine light comes on again after driving it a while.

I replaced the throttle position sensor, cleaned the throttle body and air intake, ran lucas fuel injector cleaner through it, and I sprayed starting fluid around the engine pretty much everywhere to check for vacuum leaks(none found).

I took it to the Ford Dealer and they ran a computer test and asked if I could bring it back for more diagnostics tests on Monday (it was a Saturday and they ran out of time).

The Service tech asked me if it was the original engine, if I replaced any parts, etc....

The truck was wrecked when I bought it and I had the body repaired. It got hit pretty hard. My body guy may have possibly replaced some of the components such as air intake or other things from another wrecked truck.

Again, the symptoms: RPM's Fluctuate when starting (hot and cold) and wants to stall and then settles at roughly 800 steady. Burning rich. Check engine light comes on.

Other than that, the engine is strong and runs great. No smoke but I do notice possibly excess moisture coming out of exhaust (may be normal, not sure).
Submitted: 2 years ago.
Category: Ford
Expert:  John Mc replied 2 years ago.

John Mc :

Hi, I am John Mc, a Ford dealer tech. I hope I can help you quickly and accurately. One moment while I work on your problem.

Customer :

Sounds Good

John Mc :

From your description it sounds like you either have a bad mass airflow sensor or a dirty one. I would suggest removing it and cleaning it with some electrical cleaner or brake cleaner. After this take the battery loose for 5 minutes and see if it is better. If so you just have a mass airflow sensor problem. If not follow the pcv tube from the back of the drivers valve cover around and to the intake. Check any of the rubber tube parts for rotting. They are bad about rotting out and causeing a vacuum leak, this will cause the engine to run rich with it trying to compensate. One of these two issues should be your problem. If not it is a bit more complicated and you should have someone check it.

John Mc :

Anything further and you will need some equipment to properly check out the systems.

Customer :

Is the mass airlfow sensor on top right by the air cleaner canister

John Mc :

Yes.

Customer :

I will go out and check these things.

John Mc :

ok.

John Mc :

If this answer has been helpful to you please help me by accepting. This is how I receive credit for helping you
today!

Also if you need further assistance for this problem after accepting feel free to ask a follow up and I'll be glad
to help.

Thanks,
John Mc

If you need me and it says I am not in chat it is ok. I get a message as soon as you respond so I can come
right back.

Customer :

The truck got hit pretty hard and we even had to change the valve cover on the passenger side because it had a hole in the back. The wreck may have pinched some hoses on the back side of the driver side of the valve cover area.

John Mc :

Very possible.

John Mc :

This is a pretty large hose so it is either pinched or has come loose.

Customer :

Is the hose coming out of the valve cover(driver side)?

John Mc :

Yes should be one on the back of the drivers side valve cover.

Customer :

Will be back. My guess is that the collision hurt it.

John Mc :

ok

Customer :

The two big hoses look good coming out of the back of the valve cover all the way around.

Customer :

What is that thing under the alternator that a small vacuum line plugs into?

John Mc :

Sorry, I was not notified of your reply.

John Mc :

That is the coolant control valve. This should not be a big enough leak to cause your problem. It is possible if they replaced the plastic manifold that they did not replace the gaskets. Some people try to reuse them. If this is the case it could be your vacuum leak causing all the problems. To be sure if this is a vacuum leak you need to get a scan tool and read the long fuel trims and short fuel trims. Add the long and short for bank one and then for bank 2. Each should have a total of under 10%. If not you definately have a vacuum leak. At this point you would either have a bad pcv valve itself or bad intake gaskets.

Customer :

When I unplug the mass airflow sensor the RPMs do not fluctuate. When I plug it in, the RPM's go up and down.

Customer :

Does this mean the mass airflow sensor is the problem?

John Mc :

This is very possible. As I said earlier this is a common issue with these trucks. First try cleaning and taking the battery loose for 5 minutes. If that doesn't do it then try replacing the sensor and leave the battery loose for 5 minutes.

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