OK, I'm not mocking any of the people who give great advice and help here by any means. But since this occurs under strange circumstances, it reminded me of Car Talk.
My 04 D2 with 107k throws very intermittent codes, 1174 and 1171. Generally it is only after the first time the car is started, and only after the car comes to operating temp and has been driven for a while and then idles. It is at his point when the UG shows these pending codes. I clear them and they do not return for several days. At first I thought might be the O2 sensors, but based on further inspection, they are not the originals, as the PO mechanic had to do a splice on the passenger side front connector.
I have cleaned the MAF with CRC MAF cleaner as a potential cheaper solution to new O2's.
Anyone else have this happen this way?

 

Vacuum leak

 

X2 on vac leak

 

X3 on the vac leak. I was throwing the same codes. Mine was caused by the MAF to TB tube. I thought it was tight, but it wasn't tight enough.

You can do a smoke test to try to locate leaks.

 

that should be a new heading STUMP THE CHUMP for all those question that never do get answered