97 Trooper Stalls

Hi,
I decided to take my trooper in to have the valve cover gaskets replaced and the egr passage cleaned and the egr replaced. Now my trooper intermittently stalls when I stop. It doesn't choke or try to keep going it's like someone turns off the switch. When it is in this stalling mode I have to keep one foot on the gas and one on the brake to keep it from stalling. It pumps out black smoke out of the tail pipe and accelerates very roughly until it reaches 15 or so mph. My check engine light came on and the code was P0101 MAF or VAF CKT Range/Perf. What the heck does that mean? I took it back to the mechanic but he insists it's not anything he did when he did the repairs.
I changed the plugs with the required NiponDensos and it ran great for about an hour. I thought I fixed it. Then it sat over night and stalled the next morning within the first couple minutes driving. Then after reaching my destination it was running fine. Also when I crank it first thing in the morning it doesn't idle like it did before. It used to idle for 10 seconds or so, depending on how chilly it is, at about 11 - 13 hundred rpm. Now it idles at about 6 no matter what the weather is.

Any clue?
Thanks,
--Michael

Here is what I did: I took off the air handler and sprayed carb cleaner in the throttle body as I revved the throttle with my left hand. After 10 seconds or so I noticed the black smoke quit so I let go of the throttle and it idled normally. This puzzled me and I looked at the throttle body and around the engine for about 10 minutes. Then I noticed a "sensor" plugged right into the throttle body. I unscrewed the 2 little screws and popped out what looked like a plunger with a spring on it. It had lots of carbon built up on it and wouldn't move. I cleaned it with carb cleaner till it was shiny and moved freely and replaced it. I no longer got a CEL after doing this. It stayed that way for a day while I drove it. It still stalled and had a hard time starting every now and again, but with no CEL. So I changed the fuel filter. No she's running like new again!! I found out that sensor is an idle control and was probably sticking causing the p0101 error. In combination with a clogged fuel filter, my car sputtered and spat and wouldn't run. It's my feeling that the mechanic should have cleaned that idle sensor when he cleaned the EGR passage way but then, what do I know about mechanics?

Thanks,
--Michael