S14 vibration/noise under load at stop

[SoDelMotorsports]

hello hows it going, im really hoping someone on here could shed some light into my problem, but for a while now every time i stop at a red light or just stop the car in general it starts to give a vibration and noise but instantly stops when i let off the brakes (yes its automatic for now) and or manually set the idle with my foot to about 900 rpms, on its own the car goes down into a pretty low idle (around 500rpms) and thats when it usually makes the noise/vibration, does anyone have any suggestions on what it could be? if i had a drive on lift i could diagnose the problem but i am not able to keep the car under brake load while on the lift.... up until now i still think its a motor mount showing age, anybody else have the same problem?

also the idle is never really definite it varies on several things like the heater/ or defrost usage, all kinds of stuff, so im thinking that may be an IAC

Thanks in advance!

[sx moneypit]

Sounds like you have a bad motor or transmission mount and the low idle is making it seem worse. You might want to clean the throttle body and see if that helps.

[SoDelMotorsports]

thanks a lot man, im headed out for some trial and error now....

[SoDelMotorsports]

anybody else ever experience this? any help is greatly appriciated!

[IKGamex]

I don't have the exact problem, but my engine shakes at idle and will jump around. Pretty sure it's due to a vacuum leak, that could be your problem

[prizzom]

i have a S14 with a sr20 swap and i put new motor and trans mounts and it idles rough on idle too, im sure i have a leak somewhere maybe you might too

[coupe240sxguy]

Have u ever thought of the Harmonic balancer or the drive shaft center support bearing?

[SoDelMotorsports]

all these things are on my list for checking this weekend, my brother has a lift which will make it a lot easier to get under it and find the culprit, i want to take off the intake manifold also and check all the vaccuum hoses, wish i had a vacuum diagram so i can see it all, thanks for everyones input