Flashing CEL to solid
 

Heres what happened to my buddies '98 2.5L. He tried starting the car and it seemed to have a 'weak' startup, although it did start. A day after he was driving and then the CEL started 'flashing' and the engine "rumbled or sputtered" and seemed to be significantly losing power. So, he immediately parked the car and let the car sit for about a day. Restarted it the next day, now he only gets a 'solid CEL', but the engine still loudly sputters/rumbles and a strong vibration can be felt in the engine compartment (behind driver's seat). The car seems to still have very little power.

110,000km
No other problems- ie, no oil leaks, temp is fine, etc.
No mods.

Any suggestions?

Tell your friend to get the code read.

Try and find out what codes are causing the light then post them so we can narrow it down. If the light starts to flash again don't run the engine as it can damage the emission components.

You could also disconnect the battery for a few minutes to reset the DME to basic functions.