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March 2011 Techline

Ford F150 Engine Bay
Willie Worthy | Writer
Posted March 1, 2011

Ford F-150 Issues, Death Wobble, and More!

F-150 Air/Fuel/Fluid Problems
Q My vehicle is an '02 Ford F-150 Crew Cab Lariat 4x4, stock. I have two problems: Problem 1: After driving in stop-and-go traffic, the truck will idle very low and occasionally stop running. Sometimes it idles rough, and then proceeds to die. Crank, hit the gas pedal, and off I go, but with very little power. And if the gas pedal is released, it dies too.

I suspect that temperature (bad vaporization of fuel? I've already added Lucas gas additive, to no avail) or a leaking vacuum line is the culprit. Any thoughts?

Problem 2: 7,000 miles ago, I changed the transmission fluid, using Pennzoil ATF and the best trans-fluid additive I could find. After this was done, I realized that the trans dipstick states: "Mercon V only." At that time I could not find the stuff other than in the dealership, but I prefer Castrol and Lucas additive. Question 1: Does Castrol make Mercon V-compliant oil? Question 2: Would you recommend Lucas Trans Additive? The truck has close to 80,000 miles, and I'm looking to changing the differential, transmission and transfer-case oils. Question 3: Will this prevent the gear hunting/erratic shifting that my tranny is doing, or it has something to do with Problem 1?

I would really appreciate your help, since I don't have any competent mechanic near my place other than the dealership, and they're questionable too.
Francisco Castro

A There are a lot of things that could be causing problem #1. The first thing that you should do is have a qualified mechanic take a look with a scanning tool and see if there are any trouble codes. These stored trouble codes can offer a world of information in solving the problem. I would just be guessing in anything that I say, but here are my somewhat educated guesses anyway.

The first thing I would look for-and it will only cost you a bit of time to search out-is a disconnected or leaking vacuum hose. Tug, pull, and check out each and every hose you can find. A lot more accurate way would be to use a Rotunda Vacutec 522 smoke leak detector machine (or something similar). But then again, you don't have access to one, so use your eyes.

The idle air control (IAC) valve assembly controls engine idle speed and provides a dash pot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The power control module (PCM) determines the desired idle speed or bypass air, and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the valve to control the amount of bypassed air. The PCM monitors engine rpm, and increases or decreases the IAC duty cycle in order to achieve the desired rpm. The OE part number is YL3Z9F715AA, and the cost is about $120.

Ford used at least two different manufacturers of this item. The valve is not repairable or cleanable. I am not saying that this is the problem, but just one of the things that could cause the problem.

As to problem # 2: Always use the transmission fluid that is recommended by the vehicle manufacturer. Any other fluid may not be compatible with the internal components, especially the clutch plate material. Yes, automatic transmissions have clutches that engage and disengage between gear changes and have certain friction requirements. Using the wrong fluid-and even transmission additives-that may or may not be compatible with even the proper fluid can cause all sorts of shifting problems, and very possibly the ones you're experiencing. You need to read the labeling on the fluid package as it will state what requirements that it meets, such as if it does meet the Mercon V requirements.

While there are quite a few additives available for engine oil, transmission fluid, and gear lube, it is hard to say if they really add any real benefit. The only way to really find out would be to have a testing lab do some extensive (and expensive) tests with each particular brand of lubricant used, as each has a slightly different additive package. I suggest that you drain the present fluid out of your transmission and start over again. Unfortunately, what is in the torque converter will not drain out, so you may have to make several transmission fluid changes after driving the vehicle a few miles to remove the majority of the "wrong" fluid.

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