The car is a Chipped 98 A4 (Giac) with an basic sub/amp.

The RPM's drop then rise up a second later while driving (spudders). This happens at random. Check engine light comes on for a second then goes away. When it happens the battery light does not come on. The battery voltage looks fine from the meter on the dash.

We disconnected the amp and the problem persisted. Now the check engine light is on solid and the car is in limp mode. It has not spuddered once while in limp mode.

Any suggestions?

the vag vode error said something to do with the power source.