Toyota Repair: 1994 Toyota Camry rebuilt engine vibration, balance shaft, rear view mirror

Question
QUESTION: Hi,
I have a 1994 Toyota Camry with about 187000 miles.  At about 17000 miles, I had to replace the engine (long story) but when I got the car back from the shop, it had this weird vibration.  I took it back and they fixed it.  The mechanic said that they adjusted the engine mounts and the balance shaft.  Unfortunately, they put a bad engine in - it drank a ton of oil - and a few weeks ago they put another one in that they had rebuilt.  After leaving the shop, I again felt this vibration but I was confident they could fix it because they fixed it the last time.  This time, however, they could not fix it.  He said they checked the engine mounts and centered the engine and also checked the balance shafts and it's the best they could do!
I feel the vibration in the gas pedal and sometimes I can't even see out the rear-view mirror because it vibrates as well.  The best way to describe it is that it feels like I'm driving a 3-cylinder engine instead of a 4-cylinder.  It is present in all gears and even when I put the car in neutral and rev it up.  It's a lot better at high speeds (more than 70 miles/hr) but as soon as I ease my foot off the gas I can feel the vibration pretty well.

Any ideas?  I think it's the balance shaft, but I can't be certain.  I can't be 100% sure that he actually checked the balance shaft like he said.

Thank You!!

Vinit.

ANSWER: I agree, I think the balance shaft is not installed correctly.

---------- FOLLOW-UP ----------

QUESTION: Thanks for the response!  A couple of follow up questions - would it be a question of just adjusting the timing of the balance shaft or would you actually have to take the engine apart and fix it?  Also, what would happen the engine if I kept driving it with this vibration?

Thanks.

Vinit.

Answer
The balnce shaft assembly can be removed by removing the oil pan, to get the balance shaft timed correctly requires special tools and specific instructions from the factory repair manual, not to mention a technician that knows what he's doing, doing this correctly can be time consuming as there are different thickness shims where the balancer housing attaches to the engine block as well as the correct timing procedure, what would happen? Probably nothing other than  the annoying vibration, 4 cylinder engines are by design prone to more engine vibration than a V-6 or a V-8, toyota added the balancer to reduce the vibration that is common on 4 cylinder engines.