The 2000 S10 is making a twittering sound that I associate with vacuum, because it corresponds with certain engine speeds and throttle positions. Only does a short chirp when the accelerator is worked at idle, but definitely does it under load when driving. Does not do it when floored, does it when starting up from a stop (clutch vehicle, 4 cylinder flex fuel engine)
Oddly, it does this only after warming up. It does not do it when cold. But once warmed up it is consistent. The warm up issue seems to associate it with the closed loop emissions system, but I have a more general Haynes manual, which does not have a solid year-by-year diagram of the system.
One odd part is that I can understand a straight whistle sound, but the sound is really a twittering sound, with a low frequency variation to it. Similar to whistles with the little ball in them to add a "vibrato". Heard both inside and outside. (I have eliminated the chance of POTUS being in there somewhere tweeting). The net result is almost like the sound of a knock, but does not occur when a knock should occur.
Everything that I know about that is driven by vacuum seems to be working, and the vehicle is in good shape, worth working on. I cannot find any leaks or cracks in visible hoses.
Any ideas?
Oddly, it does this only after warming up. It does not do it when cold. But once warmed up it is consistent. The warm up issue seems to associate it with the closed loop emissions system, but I have a more general Haynes manual, which does not have a solid year-by-year diagram of the system.
One odd part is that I can understand a straight whistle sound, but the sound is really a twittering sound, with a low frequency variation to it. Similar to whistles with the little ball in them to add a "vibrato". Heard both inside and outside. (I have eliminated the chance of POTUS being in there somewhere tweeting). The net result is almost like the sound of a knock, but does not occur when a knock should occur.
Everything that I know about that is driven by vacuum seems to be working, and the vehicle is in good shape, worth working on. I cannot find any leaks or cracks in visible hoses.
Any ideas?