Fox T-Bird/Cougar Forums  

To save you some time and effort,don't install that harness as you already have the correct one on your current 5.0L.
It is all the same all you have to do is swap the eec.
Explorer 5.0L will work but will have the wrong oil pan and accsesory drives.

Many people get into problems when a stock cam is replaced with an aftermarket or Ford lettered cam.
Why; is due to lobe centerlines that cause "positive" intake/exhaust valve overlap periods.
The stock camshaft actually has a small amount of "negitive" valve overlap.
Since the SD engine is 'load detected' by vacuum supplied to the MAP sensor; a cam with positive overlap causes a loss of intake vacuum affecting the MAP signal and making the engine run richer.
Since the oxygen sensors detect this, the result is to attempt to lean fuel delivery. End result is an engine that does not idle correct and tends to hunt for it's correct idle but cannot ever arrive at a final loop setting to match the idle set in computer program.

When looking at camshafts, the first parameter is to look at centerlines of 114 degrees or larger, have higher lifts, more rapid lift rates and somewhat longer durations without getting into light car cams that generally tend to lose to much low end torque for use in heavier cars.
There are from time to time, people who change cams, get into issues then ask for help and have a hard time accepting the answers to either change the cam again or convert from Speed Density to Mass Air engine control.

Some extra tech about cam overlap is at that point the piston 'pumps back' into the intake with both valves open a small amount.
This subtracts from what would be normal vacuum levels with a zero overlap profile.
This pump-back tends to contaminate the new air that gets drawn in such that low rpm is weak on torque until other dynamics begin to overcome this action then torque begins improve higher in the range where more air is now being pumped by the engine displacment.
This is the big reason why performce cams move the rpm points of torque and HP upward with increasing profile durations and overlap allowing more air to be used more efficiently.
There are a lot of fine points to this, as port velecity, flow losses, exhaust effects during overlap all play an important part.
An example of the effects of holding a valve open though not fully the same, is your 4 cycle lawn mower. Depending on the engine maker usually the cam has provisions to hold either the intake or the exhaust valve open about 40* additional duration past there normal closing point.
This is done to bleed off cylinder pressure or you would never be able to battery start or pull start the engine due to excess pressure and if the cylinder should fire, the rope breaks, hurts your hand or worse yet breaks your wrist..
Once the engine is started, the loss of cylinder pressure from holding a valve open a few thousands has little effect on the power the engine makes to do the intended job.

The reason Mass Air clears the cam problem is because these system controls do not use a MAP sensor to detect engine load but uses the air meter to measure airflow thus not being 'for the most part' affected by cam overlap. Of course cam overlap taken too far makes for rough idle for a different reason but still created initally by the cam's positive overlap period.
Hope this is of help to those who have an interest cam parmeters vs Speed Density engine control system