Sasquatch
01-28-2005, 10:02 PM
This is odd. Victim is a 1989 750il. Drive train is nice and quiet, untill I let it idle for a while.
Short version. Went to calibrate throttles. At the end it says to idle for a minimum of 5 minutes in N or P. So, I do the proceedure, and when 6 minutes of idling is up, I put it into D and pull off down the road.
Thwap thwap thwap... It sounds like a piece of rope is tied around a drive line and thwaping on the body. It is speed related, not engine. Got up to speed, kicked into N and the noise stayed with the road speed. After about 5 minuts of trying to figure out in my head what it could be, it goes away. Nice and quiet again. All good for the last two weeks.
Fast forward to today. Had one TB off to seal a leak and replace some vac. hoses. Then installed new O2 sensors and changed the transmission oil and filter. Remembering the noise, I checked out the drivline really well while it was up on the hoist. Everything looked good.
Stopped at a deserted business road to sync the throttle bodies again. After the long idle session, thwap thwap thwap again. Again it was road speed dependant and went away after 5 minutes of driving.
So, it seems to be coming from the center tunnel. My thought is that while idling, the cats are getting hot and heating up the driveline. But I can not figure out how it would make that noise, then just go away?
Any thoughts?
Short version. Went to calibrate throttles. At the end it says to idle for a minimum of 5 minutes in N or P. So, I do the proceedure, and when 6 minutes of idling is up, I put it into D and pull off down the road.
Thwap thwap thwap... It sounds like a piece of rope is tied around a drive line and thwaping on the body. It is speed related, not engine. Got up to speed, kicked into N and the noise stayed with the road speed. After about 5 minuts of trying to figure out in my head what it could be, it goes away. Nice and quiet again. All good for the last two weeks.
Fast forward to today. Had one TB off to seal a leak and replace some vac. hoses. Then installed new O2 sensors and changed the transmission oil and filter. Remembering the noise, I checked out the drivline really well while it was up on the hoist. Everything looked good.
Stopped at a deserted business road to sync the throttle bodies again. After the long idle session, thwap thwap thwap again. Again it was road speed dependant and went away after 5 minutes of driving.
So, it seems to be coming from the center tunnel. My thought is that while idling, the cats are getting hot and heating up the driveline. But I can not figure out how it would make that noise, then just go away?
Any thoughts?