I've been doing a lot of research on this site and I would like to get some feedback from you guys.
01 SS, 145k miles, all stock, regular maintenance, New parts: cat, rear O2 sensor, T-stat, temp sensor.
The car has a shudder or vibration while at speeds from 45 mph and up. It only happens when throttle is applied, let off the gas and its smooth as can be. It might just be me but it becomes more noticable when making gradual right hand curves.
The car does have the amazing wandering gas guage needle but I'm pretty sure this has nothing to do with it. Something that is interesting, I drive about 20 minutes on the highway to work. At work there is limited parking and I sometimes have to park on the side of the driveway. About 30 min after the car has sat, I'll go and move the car into a regular parking space which might only be about 20 yards from where I parked originally (car is only running for about 30 seconds), and the car will sit there for for another 8 hours. I'll come out to start it and I will have to give it a little gas to fire it up. No gas and it will just crank.
There is no CEL. Cold idle seems good.
I figure I have a fuel problem and will start with: injector cleaner. I'll then move onto fuel filter, plugs, wires, coil packs. I've read on here about the MAF sensor being a culprit too. Like I said, no codes and I really wanted to buy new tires and not just throw parts at stuff so all help is greatly appreciated. Thanks.

 

 

fuel injector cleaner is going to be a waste of $5.

When was the last actual tune-up for the car? I would recommend that first.

And if you do feel a vibration when turning it could be a wheel bearing, but I think you'd feel that more than 45 mph and up.

 

Thanks for the replies. I thought that it might have been a wheel bearing too but because it doesn't happen when there is no throttle, I figured it was unlikely. I'm not exactly sure on when a formal tune up was done, I've only owned the car since Nov. of last year. I did go through some of the service records and found that the MAF was replaced in June of '08. The previous owner kept pretty good records but I haven't seen anything mentioning fuel filter, plugs, wires, etc. I was wondering if a cv shaft could be bad. I don't have any clicking while turning though.
Appreciate all the help.

 

So I have done some more digging about my vibration and the occasinal hard start, I believe the two are not related. I am really thinking that the cv shaft is bad on the passenger side. Turning right while accelerating always cause the vibration. There is no clicking or any other types of noises coming from anywhere on the car. I'm gonna try and look at the shaft tomorrow and see if the boot is torn or anything like that.

 

I got a look at the passenger side shaft and it looks like all the grease in the boot has blown out. There is grease caked on the frame drirectly below the boot where the boot fastens closest to the tranny. The boot does not look torn nor does it look like it has become loose. It is hard to tell though. I think I found my vibration.

 

glad to hear

 

I wondered if you did find the problem yet. I have the same on my 2001 SS. Getting worse today. Only on acceleration on any right curve, there is extreme vibration (Shudder).
For the first time today, "check engine" "ABS" and "Trac off" lights on too.
After leaving car set and then restarting, only " Check Engine" light comes on, but soon after driving, the other two lights come on again.

I am driving my truck until I find what is wrong and get it repaired.

 

It could be your passenger side inner cv joints, they will cause the car to shudder on acceleration and during driving but won't start acting up until 40 mph give or take but when you let off the gas it goes away and smooths out. If this is the case my money would be on the grease in the boots on the shaft has worn down over time and your cv joints are going bad. I recently had the same issue and checked everything out. Replaced both front axles driver side first (at recommendation of a garage that apparently had no clue lol) and it didn't resolve the problem and then did the passenger side and problem gone. The vibration could be causing your wheel speed sensor to loosen up with all the vibration as it did to mine while it was happening as well. They are just clipped into the back of the wheel bearing, but it could be needing new bearings that is causing this as well, easy check is to put the car up and grab hold of the wheel at top and bottom and push and pull and see if it moves, also you will hear a noise inside of your car while driving, sounds not quite like a grinding noise and not quite like a whirring noise, but you will definitely know it is there if the bearing is gone

Also before you spend too much money make sure you give your tires a once over, and possibly balance them, this could also be causing the shake, if you live in a snowy area sometimes it builds up on the inside of the rims throwing them off balance, but it should not go away when you let of the gas it will be there all the time. But check the tires just in case.

 

Thanks. I am rather convinced now it is the CV on the passenger side. I ordered both driver side and passenger side. The excessive vibration may indeed have caused the ABS sensor to register a problem too.
Still have problems with the window switches as well. I replace one and it soon stops working or the other side stops. I have a another new master switch to have my mechanic install. I thought I could do without opening my window, but going to ATM, collecting the mail, going through fast food lines, and even venting my cigar smoke has
changed my mind. I must get both windows working.