Just wanted to give back after having read so, so many of the posts here.

I have a 99 5.7L Express Explorer Conversion Van 105k miles. Very bad hesitation when first starting out (hot or cold) but then got better. At it's worst, it also had a bad hesitation from a stand still ... like in intersections! Very concerning! Also had the Service Engine Soon light come on (and cycle off once in a while only to come back later). The Chevy Dealer said I had codes P0170 and P0174 .. lean condition on both sides. Chevy dealer replaced the fuel pump .. two different times. No improvement. They also said they did a BG fuel induction clean up ... which did seem to help with the hesitation when at intersections and such. But I still had that initial hesitation (hot or cold) when first starting the van (plus that darn light kept glowing). They were ready to change out the fuel injectors and I told them I'd pick it up ... they didn't seem to have any good reasons (that they told me) ... just seemed to be ready to change out some parts (very expensive ones at that).

Anyway, I reviewed lots of posts and here's what I did: Ran the van with Techron fuel injector cleaner in each tank of gas. Seemed to help a little ... but never solved any problem. Changed out the distributer cap and rotor ... it needed it but still no real improvement. Replaced PCV valve/tubing/elbow ($10 all-in-one part from the Chevy dealer) ... it was shot and had a break in the rubber elbow. The part from the dealer includes the PCV valve. Then I moved on to the Mass Airflow Sensor. I removed the airfilter unit, disassembled the Mass Airflow Sensor unit that is right behind the airfilter. It's a square metal block shape sandwiched in the flexible rubber air ducting. It also has an electrical connection to it. Just disconnect the electrical connector, pull the 4 torx screws out, carefully pull off the metal cover and then the MAS will pull right off. Be really careful with the MAS, it's expensive and delicate. I sprayed the daylights out of small sensor wires using CRC MAS Cleaner ($8 at PepBoys) but still two of the three wires still looked black in the center, thicker area of the wire. Almost a charred look ... I thought I was off to the parts store again. But I went ahead and got a pencil eraser (I read this in another post ... I didn't just think this up on my own) and VERY, VERY carefully rubbed the wires to get the gunk off. Be very patient and gentle! It did clean them up to where they looked like silver wires again. Then sprayed them again with the rest of the can of cleaner. Let everything dry about 20 mins and reassembled. My van is now running like it did years ago ... more power, better sounding and the SES Light went off on it's own! I have to believe that cleaning the Mass Airflow Sensor did the trick. Very, very easy to do.