I agree.
The wire harness rears it's ugly head when the wires are disturbed [ changing plug boots]
Do a search on it ..
The egr can easily be checked by using a hand vac pump to open/close it manually and chech for rough idle when open..This indicates a sticking egr , no roughtness indicates tube blockage..
EGR has ben up-graded on this model for sticking part..
The second most common egr code fault is caused by a break in the vac line under the front engine cover going to the egr Switch over valve -- this line is plastic and dries up and cracks/breaks on 104s.... without this line , the egr can not get energized...
The real code you want to verify ignition faults [ which are suspect w/plug condition] is to build a led/sw tool[archives] and go to pin #8 [HFM/SFI module ] or have it scanned...
And lastly , the infamous OVP.. this feeds power to the ECU and a bad one will raise hell with both ignition and fuel..
Check and see if it has the new part # , and if it does not , just change it for insurance sake and future problem possible elimination