My usually reliable '90 525ia is suddenly not well. The check engine light flickers on and off, and the engine RPM's surge from idle to 1200 without help from the gas peddle. I replaced the oxygen sensor and this has not helped. Car seems to run ok as long as I stay on the throttle. When I let up off the gas to slow down or stop the engine starts to sputter and sometimes stalls when I give it gas to keep it going. After stalling it will not immediately restart. Any suggestions on which way to turn?