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when in park and i rev the motor to 1800 rpms and higher and my engine will start a vibration that will pulsate on and off.The pulsation of vibration will speed up and the vibration gets finer as the rpms increase. all the way to 5000 rpms. at idle it seems fine but then again when stopped at a red light while vehicle is stopped and in drive the idle falls enough to drop the voltmeter so its not charging but when you flip it in neutral the idle speeds up and the alternator will charge again. ive had it hooked to a computer but it wont reveal anything other than i have misfires jumping around on all cylinders. but its not something you hear. just the pulsation/vibration is felt and heard clearly. its an automatic and a tech dept said i have an access cover on the bottom of the tranny where if removed i will see the weights on the ring gear which sometimes these balancing weights can detach from the ring gear and throw it out of balance. could this be true? any help is greatly appreciated.  

i think you have several problems...   that may be related ... or may not be...

misfiring... will in some cases... make the engine shake...    there are also rev limiters to prevent high rpm blasts in neutral...

how fresh is your tune ???? got 100,000 on your spark plugs..    torn boots on the wires??? or never been changed...

how is the coil....   any white dust patterns around the coil windings close to the frame of the coil;?????  that would show the coil may be leaking high voltage...

alternators die...   sometimes they quit working completely.. sometimes failing part way first...  

how swollen are your battery case ends....    still flat... or are they swollen from the cells pushing out...  if so... time to change it...

open the hood at night in a dark area....  take a look for arcing from the ignition system...  or take the ignition system apart and examine it carefully for signs of arcing.. burn through spots... tears,,  powder marks...

examine the spark plugs.. put in a new set... use spark plug anti seize on the threads... dielectric tune up grease on the boots but being careful not to get it on the tip or wire terminal inside the boot... only on the boot...... oh yea... spend the extra 99 cents...  buy 2 different ones... spark plug anti seize is for the threads...   dielectric tune up grease is for thermal transfer and high voltage insulation...  

ok. well thanx for the feedback and i will def take a real close look at the coils. but now i realize that a coil can get weak. ive had some people tell me that a coil is either good or not at all. (how dare they!). but even i didnt know they can leak voltage. you must mean corrosion? no? i bought the car with 70k miles and the previous owner said it always had this problem but he never thought to look into it. as far as the spark plugs and wires, they are new with 8mm performance wires. the car had the catylic converter removed on the passenger side but left the one on the driver side? why? i dont know. i ended up cutting the remaining one off only to find it hollowed out. the battery is a new interstate also. and where is the ignition system located anyway? i appreciate the info. also so you think the charging behavior while idling and in drive while stopped really could be the alternator or could it be from a performance issue? anyway thanx again!  

there is one more thing about alternators...  they have a low rpm cut out... so the car will be able to idle at a really low rpm...  this timeout only lasts for 2 , 5 or 10 seconds depending on the voltage regulator... the regulator programming is matched with ecm programming ...

when the engine rpms drop to a predetermined point.. the regulator stops the charging for the specified time...

the ecm is also watching the rpms.. and knows the alt has stopped.. and its counting also...  just before the alternator starts charging again... the ecm adds some idle air counts to the idle air control motor...  so the engine does not stall....

this allows the really low idle speeds without stalling...  if the regulator is wrong... or defective... you may have a problem...

and yes... the ignition coils do go bad....  and still make sparks... but not enough to jump the gap at the spark plug...

which engine do you have???  

the problem stated in the beginning is from a 98 camaro ss. it has the ls1 motor and its an automatic.