vibration at idle

[wolfloc]

i got a 87 regal with an olds 307 and recently i had quite a few problems. it seems like everytime i fix something then something else breaks. all of which i was able to fix by searching this forum (actually every problem ive ever had ive been able to diagnose and fix from searching this site and i am very grateful that this site is here) except for this one. i guess ill start at the begining. registration time comes around and i did not recieve a courtesy letter from the DMV so it slipped my mind and i actually realized it was going to expire the next day. so i go down to the dmv to pay and they tell me i need a smog because its been two years. so normally i would give my car a tuneup before getting it smogged but it was running fine and i needed registration that day so i could go to work the next day (pizza delivery driver) so even though i know better i headed over to the closest smog shop and throw it on the dyno. it fails for HCs. so despite my best effort i had to take the next day off work and give my car a tuneup. this is the first tuneup ive givin my car so i do cap rotor plugs wires and fluids. all went fine until i replace the plugs and two were cross threaded so i very carefully tap out the holes put new plugs in and then go get it smogged and it passed so i go to the dmv and get my registration and call my work and tell them ill be at work the next day. the next day i go to head to work and the car wont start. i had a bent fuel line so i replaced that still nothing. put a new coil on it and it was good to go or so i thought. the next day i start her up to head to work and i get this strange vibration that was never there before but its only at idle as soon as i give any gas it smooths out and goes away. when driving it has no problems . i can feel it in the drivers seat and it sounds like its coming from the rear bottom part of the motor.

any suggestions would be greatly appricated
sorry for the long post, i just wanted to include everything
the only things i can think of would be maybe an exhaust leak or loose flexplate but i would think those would get worse as the engine spins faster?

 

[madmaxstyle]

I've heard of a broken vibrational dampener doing that before. But it was accompanied by horrible noise too.

 

[wolfloc]

thanks for the quick reply. wouldnt the vibrational damper cause a noise to be at the front of the engine? the noise on my car is definately at the rear of the motor - it sounds like really bad an exhaust leak. thanks for your help.

 

[dan2286]

It sounds like there is a misfire or something. With the engine running, pull a plug wire one at a time and see if the engine sounds any different. If it sounds the same with a plug wire pulled, there is a problem in that cylinder.

Also, did you make sure you got the firing order correct?

 

[megaladon6]

the vib damper don't always make noise. the easy check is to pull the belts and see if the vibration goes away.
a vac leak could also be causing it (via a misfire).

 

[SV6 REGAL]

Cracked plug?

 

[wolfloc]

thank you to every one that posted. work and family obligations left me with little time to work at but i finally found it today. turns out it was a vacuum leak. once again thank you. without you guys i would be out of work.

 

[megaladon6]

if it was a vac line, i highly recommend doing all the lines to keep this from repeating.