vjd3

So, it's been really really cold here in Boston the last few days. My 95 C4, on the first start on a cold morning, exhibits a really horrendous rattling sound, sounds like rocks in a dryer, very loud inside the cabin, barely audible from outside the car with the engine lid up. Idle is smooth (once it's done hunting for the first 30 seconds, which it's always done when it's cold out), engine revs normally. Doesn't seem to occur on later starts unless the car's been sitting for a few hours. The rattling disappears after about 3 minutes or so. This leads me to believe it could be the air pump that only runs on cold start, but I'm looking for other ideas. Also curious if it's possible to easily unplug that pump to see if the noise goes away; is there an accessible harness to it in the engine compartment or a fuse/relay that doesn't affect anything else?

Again, after a couple of minutes, rattling stops, car runs normally, good power, no other issues.

TIA

epj993

I'm sure you could disconnect the air pump via the connector or fuse/relay, but my guess is that it might trigger a CEL since the pump would not be working. Also, I think the air pump only runs 90 seconds (max). Not absolutely sure for a '95, however.

I wonder if it's the transmission shaft just making more noise when very cold. Mine has a similar rattle, just very subdued.

ZombiePorsche44

I get that rattling sound when my car has not been driven for 4-5 days but it only lasts 3-4 seconds then it's smooth as glass.

I'm guessing the lifters need a second or two to pressure up after they have been sitting for a while.....anyone else have any ideas??

ZP44

vjd3

This is more like a knocking or slapping sound from the engine compartment, but it does not change in tempo or volume when the motor is revved, I'm thinking it's something ancillary to the engine itself.

slider

when you said rocks in a dryer, I was thinking timing chain, but clearly that not the deal. My car does this as well, only not so loud. after a few minutes, no noise, no issues. Kind of sounds like it is coming from the right side, for what its worth...

c993k

I was thinking timing chain too! I had that on problem an old Euro SC that I had. The tensioner was manual and the chain guides were worn out. Chris

slider

yep...that got my ol SC too...