Mitsubishi Repair: 97 Galant ES, engine trouble, balance shaft, pcv valve

Question
I have a 97 Galant with some engine trouble.  When I am driving and hit about 55-60 the whole car shakes as I accelorate.  When I ease of the gas the car stops shaking.  It doesn't do it all the time.  I thought maybe the tire needs to be balanced but the shake is too severe to be just balanced.  It feels like the engine is coming loose but the mounts are all good.  Another thing is that my car is not idling right.  I have made some minor modifications to the car about 2 yrs ago but have not had any problems till now.  I put a cusstom intake and exhaust on the car.  I appreciate you taking the time to read and respond to this.

Thanks,

Berto

Answer
Berto,
With the upgrades you added for the intake and exhaust, that allows for better air flow into the engine.  And with that extra air coming in, you'll need to be sure your fuel is being supplied adequately as well.  Your sputtering may be caused by a clogged fuel filter or clogged injector.  You should also be sure your fuel pump is working properly.  Replacing your PCV valve and giving your throttle body and EGR valve a good cleaning can also help.  

If taking care of those items doesn't seem to help, it's possible you have a worn balance shaft belt.  If your balance shaft gets out of phase, it can cause the whole car to shake and make your idle feel rough.
Good luck!