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00 SLS Vibration and Hesitation...

2245 Views 10 Replies 6 Participants Last post by  5.0guy
Hey, First let me say I'm brand new to this forum and new to owning a Cadillac so I'm sure any help you can give me would be cool.
I just got a 2000 SLS last week, and for about the first week I've been trying to get used to it and fix up any problems that I can get after. The car has 99k miles on it seems to have a shudder at idle. I wouldn't even really call it a rough idle, it's just a real slight surge that's more annoying that anything else. When you get on the gas, you kinda have to ease into it, or else there is too much of a hesitation. I searched for problems like this and it seems like the most common anwer is tune-up, but after that, is there anything that is a common problem that may cause something like that.
Also, at around 65mph-75 and then again over 90 i get a pretty pronounced vibration. is that something that would be caused by a bad motor mount, I heard that was a common problem for the front motor mount to give out.
The SES light came on once, when i tried to accelerate from 60pmh to like 80. No codes except the fuel level sensor (i'll get into this weekend), and a brake lining code.
Sorry for the long post but not sure if these issues could maybe be related. Anyway, like i said any help would be much appreciated.
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Adam -

1. :welcome:

2. Shudder at idle - usually carbon buildup around the throttle plate or around the idle plunger - check out the Northstar and Tech Tips forum for write-ups on removing and make sure you use throttle body cleaner and not carb cleaner - different chemicals. This also could be caused by a vacuum leak - perhaps a cracked plenum.

3. Hesitation - See #2 or perhaps a busted front motor mount.

4. Don't get creative performing your tune-up. Use only OEM plugs, AC Delco part 41987 - One of the vendors on the right --> or Rock Auto

5. If you do not have proof of coolant change in the last 2 years you will need to do this very soon - drain and fill - no need to flush - search this site for info on coolant sealant tabs. Use the same coolant to fill that you drain - 50/50 mix using distilled water. Change every 2 years thereafter.

6. No need for synthetic oil - 5W30 of your favorite - use the built in oil life monitor to determine interval - Go way to the top of this page and read the Cadillac Technical Archive.

7. Vibration at highways speeds - I've never had this problem - some say bad tires, bad balance, etc. Try just rotating your tires and see if that fixes / changes the problem.

8. Just about anything is available from a search of this site. Tip: I use Google to search the site as the internal search engine has some limitations. Go to a google search box and type XXXXX where XXXXX is your search term, e.g. cracked plenum
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Hey thank for the help and the quick response. I just took apart and cleaned the whole throttle body, MAF, IAC and set the TPS on my Mustang (93 5.0, as you can see from the name..:yup:) but with that you can spray mostly everything with carb cleaner, it's a little less sensitive..haha

Anyway, again, I appreciate it and have a couple of things to check out this weekend. I'll let you know how i make out with it
kranz is dead on with those suggestions, start there and if the problems don't improve/go away come back and ask more questions. Welcome and hopefully you enjoy the car as much as the rest of us enjoy ours!
Yep ^^^. For your high speed wheel vibration......If you feel the need, find a tire dealer or GM dealer with a Hunter Road Force wheel balancing machine (Google "hunter road force" and use their dealer locator) and make sure you or the tire company sequentially torques the lug nuts to 100 ft/lb. Clean wheel/rotor mounting surfaces and perfect torque (NOT an air ratchet tool) is critical to these cars.
So last weekend, i took apart the intake box and the MAF and got to the TB which was pretty dirty, I cleaned it as well as i could. After i drove it, the hesitation was still there, but the shutter at idle was a little less. After a few minutes of thinking things were better, the shutter just came back to the way it was before i cleaned it.
Last week i was in the dominican republic so the car was put off for another week.
This weekend, I recleaned the TB and took a closer look at the MAF everything looked pretty good. Replaced the air filter and after that, still same condition.
Both times i checked for cracks in the plenum but couldnt see anything. Since you guys said its usually on the bottom, i sprayed starter fluid and got no reaction in idle condition.
Any other suggestions for what this could be?
Any other/more effective ways to check the plenum.
let me know....thanks in advance.
Spraying it is the most effective way to check the plenum. Maybe you are due for plugs.
thanks for the suggestions, plugs are relatively new. i mean not old enough to cause that kinda problem. Haven't checked the EGR valve out yet. but double-checked the plenum and entire air intake area for vacuum leaks and no luck.
Maybe this will help with another suggestion, but the studder is WAYYY worse with the a/c on. Any help i'd appreciate cause i may only try a couple more things myself, but then take it to a mechanic and not deal with it. so hopefully you guys have a few more things i can try.
Pull and clean your EGR valve. Also, have you pulled codes yet?
Ok, EGR will be next on the to-do list.

Yeah, i've pulled codes and nothing. i have a brake lining code and a fuel level sensor code. thats it. reset them, and pulled them like a week later, same result.
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