Weird rattle when shutting the car off... motor mount?

[adam12hicks]

So not every time, but about 1/3 of the time I shut my 91 IS off I hear a little shutter... maybe 3 or 4 little knocks and then silence... it doesn't sound like the engine dieseling or knocking, it sounds more like something rattling, but something that's pretty stout if that makes sense?

My engine has 130k and it's a one owner car.  Other than a high idle (2k) I haven't found any issues with the drivetrain.  I have the MarkD chip in the car but it did the same thing before the chip was installed.  The only modifications I've made otherwise is suspension and removing the throttle body heater plates.

Any ideas what this could be?  Any pointers on what I should look for on the engine mounts if this were a possible culprit?

Thanks for any thoughts!

[EN318isPDX]

check your engine mounts. they sink if the fluid has run out, also you might want to explain where the clunking is coming from. my 318is had a nice clunk at the back of the tranny (guibo) but also my tranny mounts were toast. it sounded like my tranny was coming apart.

[adam12hicks]

Yeah I checked the guibo and it looks good.  The tranny mounts looked solid as well.  It's really hard to tell where the clunking is coming from, but it seems like it's happening up near the engine.  I wouldn't expect the guibo anyways since the car is in neutral when it happens so the drive shaft isn't moving.  I'll take a closer look at the engine mounts and see what I can figure out.  The weird thing is that it happens less than half the time, and I would think the engine mounts would happen every time.

I think I'm just screwed

[peerless]

Sounds like a case of the Getrag rattle. Its the layshaft in the transmission. Not much you can do about it, not much of a problem either though.

Here is the test, with the engine running and the transmission in neutral with your foot off the clutch pedal, turn off the engine. Did you hear the rattle.

Now repeat, but this time hold the clutch pedal down to take the load off the trans, did the noise go away?

[adam12hicks]

Thanks for the test procedure Peerless.  I tried it with both the clutch in and out and it didn't make the sound either way, but I will continue to test when the car has been driven and see if I can find a pattern.

[RouteZeroDesign]

You idle at 2K rpm? thats reeeaalllyy high, i drive below that most of the time
Probably because im a cheap Hippy who wants to save the rain forest, but not as much as i want to save myself money

I get the same thing that you do. When i shut the engine off, its almost as if the engine kicks from left to right.
i also get the same kinda thing when going from on throttle to off throttle quickly, almost as if the engine is jumping around because i can feel the car jerk because of it.

I think my only solution is fitting new gearbox mounts, as thats what ive been told is the problem. It should be too much hassle though, ill probably wait and do it when im putting in my 6 speed trans.