Intermittent Surge / Stumble

[BIGGER]

2002 7.3, 107,000 miles, 6 spd, Austin, TX

I have had this problem off and on for the last year. Had it again today and was hoping someone could help me out.

Intermittently at idle-1500rpm, the truck will stumble/surge. Almost like a miss. It seems to be worse when the air temperature is over 75. This morning (65F) driving the truck it ran great, plenty of power. Coming home (84F) the truck was stumbling/surging once at operating temperature. It will stumble for a few minutes then seem to run good for a few minutes.

I have a 10K resistor. When I pull the resistor all issues clear up. Rather than just pull the resistor and pretend there is no problem, I would like to pinpoint what may be wrong.

I have tried 3 different resistors, they all cause the problem intermittently. I have replaced the CPS recently and it didn't seem to have any effect. I run a BHAF that is a little dirty and about ready to be replaced. Oil was changed 2500 miles ago and the fuel filter changed at the same time.

Ideas: Bad IPR, Bad under valve cover harness?

Thanks in advance.

[BIGGER]

Also, boost is normal, EGTs are normal. Does blow a little black smoke when I get on it, but not excessive.

No check engine lights.

[szyd]

Any CEL? My money is on the UVCH.

[BIGGER]

No CEL. Does a bad UVCH always throw a code?