Missing or hesitation on medium acceleration. Sometimes will surge while at idle, rpm jumps with surge. Sets code 44 lean condition. Parts changed by mechanic shops- at 102000 miles, Spark plugs, plug wires, dist cap, rotor, water pmp and, injector flush. Parts changed by mechnic shops last month or so, vacuum tubing egr vacuum control, map sensor fuel pressure regulator, fuel pump and strainer, thermostat, 02 sensor fuel pump relay. One mechanic shop claimed they also cleaned throttle body and checked injector pulse. Three shops have given up on it and said run it until it breaks. Could a defective egr valve be the problem and how would I check it without a vacuum pump? When I push up on it and put my finger over the vacuum tube it falls back down.