5.0 rough idle/low vacuum

[fastpakr]

It's a lot of fun. There are a few minor things to sort through. The transmission is hesitant to down shift, i need to troubleshoot that a bit. But when it drops down it pulls hard.

 

[Craig0320]

Hmmm. Check to see if you have any slack in your throttle cable. I set my tps to .97 volts with the set screw.

 

[fastpakr]

I need to readjust the tps set screw back down. I tinkered with it a bit when I was chasing the cam problem and need to undo that. It's my current theory on the downshift, that the base voltage level is high enough that it doesn't catch a significant change to shift.

 

[Craig0320]

My thinking exactly!

 

[R A N G E R]

Now that the (2nd) rebuilt 5.0 is in the truck and everything is connected, I was excited to fire it up last week. Unfortunately, it idles like hot garbage and I'm struggling to nail down what's going on. If anybody wants to help solve the puzzle, here's what I know:

It's a '99 Explorer with GT40P heads and headers running the entire stock wiring harness, emissions components, etc
Roller rockers (stock 1.6 ratio)
Cam (comp XE258HR-12) (info here) is pretty mild, with springs installed to match it.

Very rough idle, tends to shut off when putting in gear. Will not restart without applying accelerator halfway (but starts cold with no throttle input).
Idles at ~10" of vacuum. Power brake assist is negligible.
Tested with booster disconnected, no change in vacuum measurement.
Shuts off immediately if IAC is disconnected.

No codes are being set.
No apparent impact from spraying starter fluid around any accessible vacuum connection (front and rear trees on drivers side, power brake booster, upper to lower joint, etc).
Using a smoke machine to detect vacuum leaks didn't demonstrate any.

The fuel is about two years old. I'm looking for a 5 gallon can so I can transfer a few gallons at a time into another vehicle and run it in that, then refill with fresh fuel.

Just a thought from an older enthusiast. Check the dwell amount on the timing. Bigger cams mixed with newer electronic ignitions add dwell to systems not designed for such.