I have a '91 F150 4x4 with a '93 5.0 rollercam Isky RV cam for ECV.
FI is batch, with speed sensor. The rollerblock engine came out of a F150 with a mass air sensor.
Possible crossover tube air injection blocked. The air hole is only 1/8". I drilled it out when the heads went back on. Didn't realize at first I had flipped the heads.

The only code that keeps coming up is the air pump.

I installed this engine with all the stock CA crap required to pass smog.

Here's the problem. I ran the truck for about 3 months (ranch truck) bumping around the ranch with a few forays into the city. Ran great. Then one day the idle starts to do the surge to the point of almost dying, then smooth out the start all over again.

The up/down surge only happens in N or Park, in drive it acts normal. We put it on the emission dyno, and it's dumping fuel like no tomorrow, way too fat. The adjustable fuel regulator made no change. We found and fixed all the vacuum leaks. I haven't put a vacuum gage yet. Possible that the cam is off, I didn't degree it in like I should have.

I have a new O2 sensor.

Now, the second part of this, my local Ford electronics guy that I know personally, after 4 hours of testing couldn't come up with an answer.

I'm going to go to another diagnostician this next week. I'd sure like to figure out what's going on with this, or at least a direction to look.

 

After reading another thread on possible same symptom problems, I replaced the throttle body sensor.... nope, didn't work.

So, as one can imagine, one goes through the thought process as how this engine works. So, back in the recesses of my brain, my engine builder was noting that the last few cams that cam in from ISKY were several degrees off. And we had a dicussion on how if the cam is off how an engine reacts.

So.....

I got out my trusty timing light, and timed the truck up to 18 degress initial. (engine builder indicaed that on average the cams were off 8 degrees)

Well, guess what cleared up, my idle. So, if I understand this correctly, my cam is off by a few degrees, and it's causing the engine vaccum to operate below 14hg. I understand that computer controlled engines need the vaccum operate properly. So, tomorrow I check vaccum to make sure I'm on the right track, double check the timeing to make sure I didn't screw up my information, and then play backyard/shadetree mechanic.

damn.... I hate when I have to redo something....

 

I have some concern that you have crossbread two engine configurations.
The 91 EEC is Speed Density with batch fire and a "302" (non HO) type cam fire order.
Replacing with a 5L Mass Air engine that has a different cam fire order will result in a loss of complete oxygen sensor tracking of all the cylinders as they fire for good fuel control, to be proper.
Unless I missunderstand your discription of the engine change, the book shows these as two different configurations in the E and F series trucks for the respective years.
You may get away with it for the farm but is not a proper match up.
The idle hunting is a problem where the EEC takes it's reference from the dist. PIP sensor for engine speed, references a table, then makes IAC continious adjustments to arrive at the corrrect idle speed (in the table) by feedback looping.
The hunt is the EEC closeing the IAC to lower the engine idle but it goes too low then opens again overshooting the reference idle and the cycle begins all over again thus the hunting because the EEC can't find the correct point.
A vacuum leak, dirty throttle body, dirty IAC, low vacuum all can bring this on.
Also consider that the MAP sees the lower and varying vacuum and adds/subtracts fuel as well as the fuel regulator also sees the varying vacuum and changes the fuel pressure to some degree.
So a stackup effect can add to the problem.
I wonder how much the cam is contributing to this problem? (lower vacuum)
To see if the EEC has learned the wrong settings by it'self, I would reboot by removing battery for about 10 minutes then starting the engine to full warm up and see if the hunting has stopped. If it does, I would say it's the results of the cross breeding and cam.
If not then clean the TB and IAC to be sure they are clear of carbon sludge.
I tried to bring you some indepth info on some things and how they work as well as possible causes since you are now at a loss as to what may be going on, by posting on the board.
Good luck.