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vibration at idle


redneck's Avatar
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12-23-03, 05:10 AM   #1  
redneck
vibration at idle

Ok, this '95 buick regal with 3.8 has a vibration at idle. It is there as soon as you start it. You can feel it slowly disappear as you bring the rpms up. The car starts and runs great, plently of power and very smooth (once you get rpms up alittle) and quiet. No check engine light. I verified spark from each coil and at each plug. I am thinking engine mount, but the engine does not "rock" excessively when you blip the throttle!? Every now and then at idle in drive with brake on you can feel a slight thumping like something is hitting the floor pan--give it gas and it is gone. You can actually put your hand on the engine and feel it, and even see the front wheels shake when you first start it. Like I said the engine is quiet (no miss) and you can not feel any internal thumping (like a bad bearing). Just the vibration or "shake". Gonna try pulling the serp belt tonight to eliminate the accesorys. Do harmonic balancers go bad at 79,000 miles?

 
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12-23-03, 05:49 AM   #2  
Yes these are known for splitting the balancer in the elastomer. I would also say it still sounds like a misfire problem. A cylinder power balance test, or a run on an oscilloscope will reveal what's happening in each cylinder. If you can't get access to any of that equipment, start by examining each spark plug.

 
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12-23-03, 08:07 AM   #3  
redneck
Yama, What would cause a misfire other than a bad plug wire? I went over them real good with my hands and no shock! May pull plugs tonight also--just to get a look.

 
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12-23-03, 08:09 AM   #4  
redneck
Also, the elastomer is encased in steel how do you check for a bad balancer?

 
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12-23-03, 09:29 AM   #5  
You can rock the belt back and forth and watch the pulley move without the crank moving. All of the dampners i have seen were not encased in metal

 
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12-23-03, 10:53 AM   #6  
Thats not metal, its paint. The balancer is 2 pieces of steel with a rubber "elastomer" ring between them. It sounds to me like you might have a miss due to a vacuum leak or a stopped up EGR valve. This is common on these things too.
Billy

 
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12-23-03, 11:35 AM   #7  
redneck
Your right about the balancer--just never saw one go bad--have rebuilt old pontiacs and reused balancers. I gotta look at this thing closer! The dude I bought it off put a water pump on it and never put back the radiator overflow tank--and with the wheel speed sensor disconnected--makes me wonder what else he forgot. I did see a red two prong connector behind the power steering res. that was not connected to anything--but could not find anything to connect it too! I thought about the EGR--but the last one I replaced (3.1L) did not act like this, the vac. leak is also not out of the question--they were all connected but looked dry. Also noticed only driverside fan turns on, so I turned AC on (cold out so can't tell if it works) but the pass. side fan did not come on (which is odd because the last one I had the AC was completely inoperable and the fan would still kick on when you turned AC on). I will figure this out. PS, the gas cap and donut spare were also missing! Wierd cause the car is in very nice shape, completely loaded, and all power stuff still works, no cracks in leather, and was kept waxed due to all the residue in the seams!

 
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12-23-03, 03:20 PM   #8  
Unfortunately it sounds like you got a Pig in a Poke. May take lots of time and money to straighten this thing out. Just from what you have said, this guy may have mucked with alot of stuff.
Good Luck,
Billy

 
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12-23-03, 05:28 PM   #9  
A lot of things can cause a cylinder misfire. From an ignition module, coil, ignition wire, spark plug, injector, injector driver, lean misfire, vacuum leak, EGR problem, carbon, valve timing...Get the picture? Keep it simple though and start with the basics first. Check those spark plugs.

 
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12-24-03, 05:16 AM   #10  
redneck
Naw, no pig, got it cheap--work beater--actually drove it in today--I drive 100 round trip per day at 75 plus. Runs great on the highway! Screw the vibration at idle and the stupid ABS light--I gonna drive this sucker! I did check out the balancer and pulled the plugs last night--balancer has metal ring on inside and outside--center is rubber--could not get it to slip. The plugs looked new!

 
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12-24-03, 08:56 AM   #11  
mike from nj
do you feel like doing a compression test?

my parents had an older oldsmobile, with the same 3800 V6. it developed a rough idle around 70,000ish miles. pulled the plugs, #5 was all coated with soot, the rest were clean. did a compression test, #5 was low, did a leakdown test and air was shooting out the tailpipe.

cool, we have an extended warranty, let's take it to the dealer. valves are considered maintenance, and a valve job is not warranty, they wouldn't touch it. i let them know who was #1, and with the appropriate finger.

they ended up driving it til 196,000 miles (traded in)and it never got worse, still passed inspection, and smoothed out just like yours when off idle.



thought you might want to know

 
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12-29-03, 05:23 AM   #12  
redneck
Well, that is interesting, I am not going to give up on this, but will continue driving it and working on it when I have time and keep you guys posted as to the results. Heck it may just need a tune up. I will start this weekend with plugs, wires, remove and clean EGR valve, O2 sensor, fuel filter, and may just do a comp. test (that is a good idea--got a comp. tester hanging on the wall). The wife just told me my '98 GMC 5.7 is idling rough at 80k--this truck has never done anything but idle smooth at 500rpm! Talked to my buddy, he said his truck (same truck) started to idle alittle rough at 70k and plugs and wires fixed it--so much for the 100k tune up GM advertises! The truck is more like a "studder" unlike the buick "vibration".

 
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01-05-04, 09:35 AM   #13  
redneck
Ok, update. Plugs/wires good, EGR valve good, PVC good, fresh oil, trans fluid/filter, air filter, and fuel filter, compression good. I made the wife drive it while I sat in pass. seat--you can really feel the vibration on that side! Actually can hear something "thumping" like something is loose. So this brings me back to one of my earliest ideas--a motor/trans mount! When I was under the car the mount on the pass. side looked "seperated" like the rubber was not bonded at the bottom?! But, could not see any movement of the mount while idling. How many mounts does this car have other than the "dog bone" on top? And are they hard to change? Looks like bolts are nearly impossible to get to!

 
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01-06-04, 04:11 AM   #14  
Stop looking for engine problems for a minute. Check 2 things.
First look underneath for the exhaust system contacting metal anywhere. Rap on the system and listen
Second, closely check your motor mounts. Try putting a floor jack under the oil pan and jack slighty with the engine idling in gear. Does the vibration go away? Bad motor mounts with cause this.

 
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01-06-04, 06:00 AM   #15  
redneck
Another update, pulled serp. belt to eliminate any driven possibilities (not it), marked the balancer to check for slippage (none), and jacked up car to get real good look at mounts (they are fine) I used a large pry bar to lift up on motor/trans at all three mounts and the rubber is connected at both ends. Also, checked for anything loose like exhaust (everything tight). I was under the car at idle and could only see the engine "shake", but could not hear anything "thumping", but could while sitting in the car. I guess it is time to look at the technical stuff that may be causing a "miss" ie. injectors, coil pack, etc. The "shake" it apperent at idle approx. 800-900 rpms, then the "thump" at 1000-1100 rpms, above that it seems smooth. In gear or out, same thing. Also checked very closely for vac. leaks.

 
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01-06-04, 07:17 AM   #16  
redneck
Oh ya, I forgot the O2 sensor, I was going to replace it as part of the tune up, but just remembered I saw two of them, one in front of convertor and one behind--should I replace them both?

 
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01-06-04, 03:14 PM   #17  
Don't worry about you O/2's right now. They aren't your problem. Do you know for a fact that it is misfiring? If so, do you know which cylinder? Just because your motor mounts aren't broken doen't mean they aren't sagging enough to stop isolating. As far as the exhaust system is concerned, your not looking for anything loose. Your looking for a spot that it may be contacting the body somewhere. That will transmit engine vibration right into the passenger compartment. I can't help but think it's an insulation problem and nothing to do with the way the engine runs. Try what I told you with a floor jack on the oil pan and see if it changes anything.

 
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01-06-04, 03:28 PM   #18  
Change the motor/tranmisson mounts. They wear out and get hard. You can't test them by looking at them or prying on them. I had the same problem with GMC van. It took care of 80% of the vibration at idle.

 
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01-07-04, 05:00 AM   #19  
redneck
I tried the floor jack last night, put it right under tranny pan and jacked it up with enough pressure to slightly lift the assembly--no change, in fact you could feel the vib holding the handle to the floor jack! Double checked my paint marks on the balancer (still has'nt slipped), then pulled all the plugs again and lined them up in order (they all look the same--like new). Maybe its nothing--we'll see cause I'm puttin 100 hard miles per day on her! It does not seem like a misfire cause it runs perfect and vary strong--you floor this thing and it spins the tires till you let off! If you pull a plug wire or cross one it runs like crap--different than just a vibration. Could be just old mounts--but if that is all it is I will just run it cause that don't look like an easy job!

 
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01-19-04, 02:31 PM   #20  
redneck
Well, I'm ready to order two engine mounts and one trans mount. When you pry on the engine at any of the mounts it is like rubber bands holding the engine in place--I can easily move the engine up an inch at any mount. The rubber is still attached, just very weak. Comparing to my '98 GMC, you can't hardly move the engine at all when prying at the mount! What do you all think?

 
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