1999 volvo v70 cross country. Engine surge

[Ptbsjb]

I've been reading posts for hours and I think I'm more confused. I bought my teenage son a 1999 volvo v70 cross country with 201k. The car runs well most of the time but once or twice a day it surges and sputters while travelling down the road at highway speeds and sometimes while accelerating. No issues at idle and no warning lights on. Is this the ecm, bad coil or turbo boost? I've replaced the plugs and fuel filter. Any help will be greatly appreciated. Thanks

[precopster]

ETM is electronic throttle module
ECM is engine control module

The ETM is what affects the 99 and 00 P80 cars.

If one of the coil packs is beginning to break down a stuttering will occur. It won't report a code until almost total failure.

Both Turbo boost sensors and ETMs can cause surging as can a faulty MAF (mass airflow sensor)