My 2004 Jeep Liberty has 213K miles and other than replacing normal wear items has been extremely reliable. On routine start the engine started missing as if only 2-3 cylinders were firing and the check engine light started flashing. Running too poorly to drive so I called a wrecker for towing to garage. Mechanic said scanner showed multiple misfiring and advised the computer was probably faulty. He replaced the computer and said running was improved but misfiring continued with multiple codes showing. He has had the Jeep for a week and still has been unable to fix or find the problem. Suggestions please.