7.3 Superduty stumbles when returning to idle

[Kevin 007]

1999 7.3 Superduty ZF6, when coasting in gear, no throttle for any length of time, then the clutch is depressed and engine is allowed to return to idle; the idle will keep dropping below 500rpm then catches itself just before it stalls and then settles and a nice steady smooth idle. It does this hot or cold. IPR duty cycle at hot idle is as low a 6% and never exceeds low 30's at WOT. ICP readings hover around 500 at idle and about high 2000's at WOT. Fuel pressure regulator replaced with one from dieselorings with a 61-65psi spring. Fuel filter changed, CPS and ICP sensors changes. EBPV replaced but sensor might be bad, still throwing an EBP code. Or could that EBPV be stuck? Tried replacing the IPR, got the new one on with nut on good and snug, truck ran like crap and didn't clear up after about 20 mins of run time. Both at idle and throttle. Put old one back in and instantly ran good again.
I have not yet checked my ACTUAL fuel pressure readings. And running 5W-40 Rotella t6. Any thoughts as to whats causing it to want to stall? Runs great otherwise aside from it being slow to start. Cranking speed is up but it does take longer for the engine to actually catch, both hot and cold; opposed to others. No oil in filter housing and IPR duty cycle doesn't go past mid 30's when cranking which makes me think the injector orings might be ok?

 

[79jasper]

First I would ditch the junk t6.

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[Kevin 007]

Mobil 1 instead? That's what I usually use. I was in a pinch when I bought the T6. Just got the truck, wanted to dump whatever was in it asap. T6 is all I had that day. And Baldwin 7039 filter

 

[79jasper]

Sure. That would be better than t6. Lol

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[Kevin 007]

Changed it today, Mobil 5w-40 TDT. No change

 

[79jasper]

This seems to be fairly common with some trucks.
I want to say you can't have the pcm flashed to a different box code, and that will make it stop.

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[Kevin 007]

Hmmm, you say it can't? If it could, would that be a dealer thing? Today it even stalled once, it didn't catch itself in time and it quit in the middle of an intersection. Fired up no prob but still not good.

 

[79jasper]

Oops.
"Can."
You may contact Justin at dp tuner and see what he recommends.
I would say if it's actually stalling, something is wrong.
Try unplugging the icp sensor.
New doesn't mean it's good.


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[OLDBULL8]

First I would ditch the junk t6.

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What's wrong with the T6? That's what I'm running in my 99, no problems with it, runs great.

 

[79jasper]

A handful of trucks seem to run "okay" with it.
While 90% of the rest run like crap on it.

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[greenskeeper]

First I would ditch the junk t6.

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Interesting.

I have over 440k miles (combined) between both my trucks running T6 with absolutely no problems at all.

 

[OLDBULL8]

Could it possibly the throttle position sensor or idle sensor is worn or have a loose connection.

 

[79jasper]

Sometimes the ivs needs adjustment.
Can search for pedal blue printing.

Like I said, few have decent luck with t6, the rest of the trucks run like crap on it.

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[Kevin 007]

Good thoughts on the IVS and throttle sensor. I will continue to troubleshoot