Apparently the maf is very sensitive, and the sensing wire inside should not even be touched. If they touched it in the least, it's probably junk. You should start by checking the maf wiring harness to see if they dislodged it somehow.
The 4 cyl has a maf, not a vaf like the v6. It's a fine wire that can be cleaned, but with extreme caution. Here is a writeup if you choose to clean it, but make sure you use electronic parts cleaner or MAF cleaner...these leave no residue, unlike other spray cleaners.Does the plunger move okay still?