OK. . .replaced the OVP on my 89 300E as recommended. . .no change. Car drives exactly as it did before. . .idle may even be a touch rougher than before. On warm restart, it'll stall after the first try. On the second try it starts, idles roughly for a few minutes and gradually smooths out. Plan B?

Should I replace the fuel pump check valve? If so. . .where is it located?

Thanks.