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Originally Posted by sixto
A bobbing shut-off lever is definitely not normal. There should be spring tension keeping it in the vertical position. Disconnect the vacuum line to the shut-off actuator. There should be no vacuum at the line while the engine is running (key in run or start position). If the shut-off lever stops bobbing, it's a vacuum problem, most likely at the key switch. If the shut-off lever continues bobbing, save up for a rebuild or replacement IP :/
If there is a next time, pop the hood as soon as you can without touching the key and check the position of the shut-off lever. If it's down, it's more likely a bad key vacuum switch than fuel supply problem. An alternative is to temporarily tee a vacuum gauge to the shut-off actuator line and monitor from the driver seat.
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This is the first time I heard that the shutoff levers weren't supposed to move a little while the thing is running. I'll keep a closer eye on that, but I suspect it may be related. I already have a vacuum line routed from the hood compartment through the ashtray to the inside, I think we were going to use it for a boost gauge one time. Assuming it's long enough, I'll put the Mityvac in line with the shutoff line and watch while I'm driving. This is a sporadic occurence, but when it happens I should notice the gauge move.
Quote:
Originally Posted by sixto
In my experience the shut-off lever is not a very effective fuel cut device. If you press down on it slowly, the engine might not shut off. I'll confirm when I remember to do so but I suspect it takes more vacuum to shut off the engine at 3000 rpm than at idle. If so, this lends more credence to the scenario of vacuum leaking past the key switch.
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Mine is VERY effective. Doesn't matter what speed you press mine down, when it's about 2/3 of the way down the engine starts struggling and very shortly dies completely and instantly when you press harder.
Quote:
Originally Posted by sixto
ELR only matters at idle. You can disconnect the alternator and battery and the engine will run normally. Idle will be low if it idles at all. Disconnect ELR from the round plastic thing at the tail end of the IP and see for yourself.
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When my battery died completely last month, the car refused to idle but would run just fine. So I think you're right, but I'll check just to be sure it's working.
Quote:
Originally Posted by sixto
The typical fuel supply and clogged oxidation catalyst symptoms are inability to rev the engine. The fact that you can restart immediately and get going again suggests the problem is at or downstream of the IP. The fact that it only happens at or near idle suggests it's not a bad return line check valve.
Getting into exotic scenarios, maybe the IP timer gets stuck in some advanced position at which idle cannot be sustained. The jolt of the engine shutting off resets the timer so it's ready for a restart. Seems far fetched to me.
edit - I was speaking theoretically about disconnecting the alternator and battery. You can damage the alternator by disconnecting the battery while the engine's running.
Sixto
87 300D
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Here's hoping it's something cheaper than the IP.