So I had that issue that I thought was a bad TCCS. I took the car in while it was still covered under warranty. They're telling me that I had a broken front motor mount which was causing the engine to jump around causing the 'bucking' sensation that I was describing. The bill was $400.
I'm trying to figure out why a car with 25k miles on it has a broken motor mount?
Because you're too hard on the throttle!!! My 2000 STS just had it's motor mount changed as well. And I am VERY hard on the throttle!
But I have heard that the motor mounts on these cars aren't the strongest.
Wow interesting. I would never think that. Well what does the upgrade cost cuz 'm sure I'll break it again. To tell you the truth I'm not in it a lot. I mean I drive the car but I'm not constantly on the throttle and I certainly don't beat on it.
It was $300. A bit pricy, but worth the money for me. I usually drive with my foot near or at the floor so I figured why not go with something that I'll never have to replace again. I put it in myself too, so I saved some money there. If you do go this route, the only thing I suggest is that your generously apply the red loctite when you install it. I had the top bolt come loose on me because of that, which is why I had to pull it out and re-install it. Completely my fault. It has only come loose once more and that was because of a drainage ditch I drove over which kinda bent the cradle a little and loosened the bottom bolt. Other than that, it's worked flawlessly. The mount itself is basically a solid block of aluminum with a poly-urethane bushing at the top, and two threaded sections of bolts (no head, just the shafts) used to secure it with the stock nuts.
As far as vibrations, the engine was always a little on the rough side (something I've heard is somewhat common in '98-99 L37 engines), but I didn't really notice any increase in vibration. For the first week or so, the only thing I did notice was that there was a very slight vibration just off idle which which I stopped noticing after the first week (I got used to it, and don't notice it any more). The throttle is a little bit more responsive as well since there is much less engine moviement under load. Other than that, it drives just like it did when it had a working hydraulic mount in it.
As far as ease of installation, yes, it can be done without a lift, although I think it would require more than an hour and a half (I did have a lift). If you an get the front of the car about 2ft up in the air, that should give you enough room to work I think. The way I went about accessing and removing the mount was this.
1). With the vehicle in the air, remove the nut holding the base of the mount to the front of the subframe.
2). With a jack supporting the front of the subframe, remove the front two bolts securing the sub-frame to the vehicle. Then at the rear of the sub-frame, remove the two bolts (there are four) closest to the front of the vehicle).
3). Now, using the jack, lower the sub-frame down at the front until you have enough room to reach up and loosen the top nut on the mount (attached to a brace which is affixed to the exhaust manifold). If needed, you can pull down on the sub-frame to make room, just becareful not to stress the brake lines running to the ABS motor which is also mounted on the front of the sub-frame. You may also want to remove the bolts that hold the brace to the engine and exhaust manifold as this will give you more room to work and make removal of the mount easier.
4). Once you have everything loose, you can pull it all out the the gap between the front sub-frame rail and the car.
5). Upone re-assembly, I would recommend slipping the mount in first, and the placing the brace in over it. This way you don't have to fight for room trying to squeeze the mount in around the brace. After you have it all layed out, attache the nut holding the mount to the brace. The attached the brace back to the engine. Finally, use the jack to raise the sub-frame back up into position and secure the lower nut attaching the mount to the sub-frame.
6). The last step will be re-installing the four large bolts you removed to drop the subframe. These are a real pain. I would recommend using a torque wrench on these if you can. I think they are torqued to 150 ft/lb's if I recal correctly. They are difficult but doable none the less.
It sounds alot more complicated than it really is. The hardest part for me was getting to the two bolts at the top of the brace. I needed two extensions, and a swivel attachement to get up there. That took up more of my time. Everything thing else is pretty much strighforward and right in font of you. I would say that with the right tools, and a good jack and some good jack stands, it might take you tow and a half to three hours (maybe a little bit more) without a lift. It really is a hell of alot easier if you have access to a lift, but it can be done wihtout one. I think a few people here on this forum have done this wihtout a lift, so it can be done.