shuddering @ 3500rpms

grinding/shuddering/vibration/weird noises are occuring around 3500 rpms in every gear

I've just replaced every mount my car has (3 sti group-n mounts and upgraded tranny mount with ralitek race bushing)

The problem was occuring much worse before the mounts were replaced, so I assumed it was engine movement, and so I kept my engine below 3500 rpms for the last month till I could afford to have them replaced, well now that they are replaced the same thing is happening, but much less extreme

before whereas I thought the engine would literally shake free of the car, now its an annoying "something not quite right" feel is all thats left

it goes away once I get to 4K RPMS, but if I gently accelerate through 3500rpms my car protests, but not under WOT, it just kinda hessitates very slightly, then continues on as if nothing is wrong



my first thought was that my tranny is truley starting to fail on me, further evidenced by the 5 seconds it takes me to shift from reverse to drive and how weak the car feels in general


its amazing how much abuse these engines can take, as far as I can tell the engine is in great shape at 178K miles, the last 25K of which have been spent on an 85 wet shot of nitrous lol

i started noticing the 3500rpm shudder after i replaced my axle and had my tranny mount replaced but before the motor mounts were replaced, so I assumed it was motor mount issues, but now I'm wondering if maybe it has something to do with the axle????? i wouldn't think i would get the same effect at the same engine speed unless it was something directly related to the engine

having spark plugs and wires replace right now, maybe that will do something

oh, and 3000 rpms is when my nitrous kicks in....

strangely enough, the new plugs, wires, and restarting the ECU all but solved the issue, now I just have a little extra boxer growl at 3200 rpms and is gone by 3500.... no clue what it is, but it doesn't seem to be doing anything bad

oh, and wow what a difference the plugs and wires made... 120K miles on the old plugs, original wires.... you can just feel that the car is happier in the lower end and is smoother throughout the powerband, ended up using the NGK platinums because that was all the mechanic had on hand, and he gave me them for the same price as the coppers, since he fucked up and ordered the wrong plugs, but the wires are badass black wires from hell, now my whole engine bay is black, nothing red or blue or anythin like that, just black on black on black.... in a white car. :-D