Is there a check engine light no, almost sounds like your ECU is in the "limp home mode" If a sensor or component is bad the ECU nearly shuts the engine down inorder to protect it. OBD2 scanner can read any pending codes. Had a bad O2 sensor on my 99 C70 - seemed like there was water in the gas, would run rough and not idle well. Replaced the O2 sensor and reset the ECU - like new now. Similar occurance on my 89 760 when the CAT went bad - no check engine lights but car went into the "lmp home mode" Good luck