Vibrating/Rumbling...What is it???

[PrOjEcT_LS2000]

Alright guys, for those LS engine experts... I have a 200 Lincoln LS (191,000 miles) I've searched for the answer but can't seem to find what im looking for. Some stories are close but not quite like my experience. My issue is that I have a strange vibrating/rumbling coming from underneath the front end of the car. I did have a couple of problems that I did get fixed which included a vacuum leak and a severe oil leak. All together the mechanic replaced, intake gasket kit, PCV valve assembly, PCV elbow hose, all spark plugs, valve cover gasket, 3 ignition coils, 3 ignition coil boots, and a fuel injection...about $1800 dollars worth of repair. Engine light got fixed and no other codes are appearing from the car. After all the fixes, i still have this vibrating under the car, sometimes light and then at times it vibrates the whole car. It happens when i brake as I'm going into a turn, when i put the car in reverse, and sometimes just at a normal stop. The mechanic took it through a road test, nothing wrong with the tranny and the car is shifting fine. They took a closer look, lifting my LS with it running because they thought maybe my exhaust were touching parts of the car it shouldn't in which makes the vibrating occur. That was not the case, instead he insisted that both motor mounts were bad and need to be replaced. Said that the oil leaked onto them and weakened them. Does that sound correct?? I hate going to multiple mechanics being told several different things. So far this mechanic has been correct and solved all my other problems.

 

[G-RELL]

could be. it'd be an easy / cheap fix to find out

 

[joegr]

From this great distance, motor mounts was going to be my guess even before you mentioned them.

Also, I would replace the other three COPs and plugs.

 

[Kumba]

Easy way to test motor mounts is to pop the hood, and hold your foot on the brake as you put it in drive or reverse. If the engine moves much at all then you have bad mounts. If it moves in drive, then the right passengers side is bad. If it moves in reverse then it's the drivers. You should shift to neutral for a few seconds before going between gears to make sure you get a good read on what is going on.

You shouldn't need to give the engine gas to see if a mount is broken. If it's broken then it will move by just putting it in gear. If you think it's weak, then smash the brakes and give the car a LITTLE gas. If the intake manifold lifts up or moves more then a 1/2" or so you need new mounts. I would advise doing this in an empty parking lot or street with no obstacles like people and cars. If your foot slips off the brake the car will launch and that could be bad.