I've been working on my one week old '01 F250 SD SC V10 with 105K miles getting it ready for a trip next week pulling my new boat. Never had a truck, never had more than inline 5-cyl.

When I start it hot it shoots up to 1700rpm, then it settles around 1100-1200 within like 5sec. Then after 30sec it slowly settles down to around 900-1000 where it remains. It dosn't seem to hunt as the drops in rpm are relatively smooth but slow. A couple other things I've noticed is when I'm at a stop light there's a bit of a shake but not bad, and while testing today I decided to put it in 'N' while coasting about 30-35mph it would not drop below 1200rpm. While driving it feels pretty smooth and I've been trying to notice any misfires but I just can't tell. It seems to have good acceleration from a stop but when I'm cruising down the highway and stomp on the gas, it downshifts without much drama and it proceeds to accelerate, but it just doesn't feel "urgent" like I think it should. It kinda feels like the tranny is slipping and so it doesn't "kick" you in the rear. But I'm still "lean"ing towards a mixture problem.

Here's what I've done so far. I replace the maf since I couldn't get the old one clean, even with a q-tip. I replace all plugs and boots. Most of the boots where in ok shape and I noticed the pass side bank plugs showed a lean white color. I'm in SFBay area so just a small amount of rust on the plugs as well. I forgot to make notice of the driver's side plugs, darn. My first thought is they might be original or otherwise plenty of miles on them. I replaced both O2 sensors as the old sensors had a white haze on them and thought those were original too. I cleaned the AIS which was dirty and when I pull the plug the rpm's drop. I removed and cleaned the throttle body as it was pretty dirty with black crud. I replaced the air filter and fuel filter. So a ton of searches has got me this far and I'm now scratching my head.

Almost forgot, I took it to Autozone and they made me purchase a scanner to do it myself and then refunded my money. So I plugged it in under the dash and followed the instructions which was basically "press READ". No codes. Was also thinking of going to AAMCO to get a tranny flush and check from slipping.

Thanks!!!

 

Your 01 in San fran is a Calif truck with a Calif program in the PCM
You also have clean air blended fuel
Your truck sound about right
The 4R100 is probably due a rebuild slash upgrade with thah many Bay Area (hills) miles

Early 99-03 Ford SuperDuty trucks had some very good and some very bad PCM programs, there are about 2 dozen possible combinations for PCM "codes" that the Ford Tech can apply

 

Maybe someone can correct me, but do these engines use a Idle Air Control Valve. If so, your symptoms sound exactly like the symptoms of my '93 Inline 6 when the IACV went out. In fact if I was cruising on a flat piece of interstate, I could take my foot off of the acclerator, and the truck would almost maintain 65mph for quite a ways before slowing down. The idle was extremely irratic, sometimes hitting 2000rpm and/or hovering around 1200rpm to 1500rpm before settling down. Turned out the Idle Air Control Valve would no longer remain closed when being driven.

Feel free to correct me if I'm wrong about the V10s having this device.

RustyFuryIII

 

Oops, not AIS but IAC. Geez that wasn't even close. I cleaned the IAC which still has some carbon build-up afterwards. When I unplug it while idling the rpm's drop. But does this simple test prove the IAC is "ok"???

Your symptoms of almost acting like cruise control at highway speeds is exactly what mine does as well. Seems like I can coast forever.

I also just got back from a muffler shop and I don't think my cat is clogged either. So today I'm going to go thru the whole intake and search for a vacuum leak. Btw, everything I've done has helped boost performance but only marginally.

 

Change the fuel filter and check the fuel pressure.

That slow idle coming down at cold startup is normal, at least for me, since brand-new (mine is a 2001 SC SB too).

I would also reset the computer. Disconnect the battery and let it relearn everything.

Back around 2003, some here with 2000/2001 V10's had pecular pinging problems that went away when the computer was reset and never came back. Others had sluggishness, and resetting the computer made it go away. I myself had that happen. I think this range of years has a bug in the spark time algorithm and they can peg themselves advanced or retarded and never come back. I just never wanted to mess with success and have the dealer re-flash my computer with newer code