Hello from Brian sansone . I just finished doing a partial engine overhaul on my 88 chevy tbi 350 . I had the heads serviced , replaced the rod bearings , piston rings , lifters , and two connecting rods - wich I had checked and reconditioned at a reputable machine shop . Now I seem to have an engine vibration . The vibration ONLY occures at idle in gear when I have my foot on the brake. As soon as I give it some gas , it runs as smooth and quiet as a brand new engine . The vibration is very fast , it makes the cab of my truck resonate like the inside of a bass speaker . When trying to observe the engine in this vibrating state I noticed that it was vibrating so fast that I could not read any lables on the engine or accesories . They appeared as blury as if I had been drinking all day -not the case - at any other rpm the engine runs perfectly smooth and steady . Could this be a failing harmonic balancer ? I put ALOT of undeserved stress on the balancer bolt during the rebuild ; especially when taking the old pistons out . Could I have damaged it . Is there a way to check it ? Or could the two rods from the foreign engine be the culprit . I realize a vibration could be from any number of sources . But I am tempted to think it is from one of these two sources. Truck ran fine before I did all this work . Any advice will be much appreciated . Any Chevy Guys ?