Help Another Surging Mustang

[z3beemer]

Ok, out of ideas and need some help from all you experts out there. 95gt 5.0 pretty much stock other than air intake, pulleys and Xpipe. Been running fine and no new mods. Car starts surging and running rough at idle once the thermostat open and even get worse when the fan kicks on. Stalls sometimes when coming to a stop and even surges at times at cruising speeds. So far we code scaned all OK on hard codes and engine run codes; get a 211 and 213 as stored codes. Have changed tfi module, coolant temp module, cap and rotor. Still same problem. Checked for ground and vacuum leaks, none found. One other symptom. when disconnecting the SPOUT and attembting to check base timing the timing light only seems to light once couple revelutions but lights consistently with the SPOUT connected. Could this be a fuel pump; filter; regulator or injector problem?
I originally rule this out because the problem doesn't show up until the thermostat opens. I'm out of ideas.

Thanks in advance for the help!
Paul