The car has run so well for so long, until...
Went for 30 minute drive last weekend, mixed town/highway. Car started fine, but I noticed it ran a bit rough under light load at anything under 2k rpms. The problem at idle was barely noticeable, with just a tiny bit of stumble. But the car would splutter until the engine was above 2k. Above 2k there was no issue, ran on highway at 70 mph with no issues. But back in lower revs the problem was still there and persisted for all 10 remaining miles of the trip. I parked the car for about 45 minutes, started it up for the return trip and the problem had disappeared! The car ran perfectly for the entire 30 minute return trip.
Went for a drive today and the problem was back, exactly as last weekend. I drove about 20 minutes, then shut the engine off, let it cool 20 minutes and started up again, hoping the issues would resolve as it did last weekend. No such luck, the problem is still there.
Now, I don't want to send anyone down a blind alley, but I have also recently noticed that the whine of the fuel pump has a different quality to it, it is sort of a two-tone whine where as for the last 10 years it has always been a steady, single high-pitched whine. I assume the pump is getting tired (bearing worn?), but I can't imagine how it is related to the stumbling issue, given that the car runs great at full song.
I assume something is sticking, but don't know where to start to diagnose, would really appreciate some advice.
Thanks,
greg
'64 230sl, fully sorted out...ooops, spoke too soon