I recently took over driving the 240 wagon that used to be my wife's daily driver. I've noticed that when lifting off the brake pedal the idle drops a good amount, but then usually recovers fairly quickly. Once or twice, it has actually stalled when I let off the brake. I am going to clean a few things tomorrow. I suspect some kind of relation to engine vacuum. I know the stalling isn't normal, but is the drop in idle typical? Is there some kind of test to check if the booster diaphragm has gone?