About 15 months ago the Toyota dealer replaced the timing belt on my 99 V6 4Runner. About 6 months ago I occasionally began getting a flashing check engine light at highway speed suggesting a random missfire. Gas mileage was also down a bit and idle was a bit rough. The dealer replaced an ignition coil and that did not solve the problem. Just recently I asked the dealer to change spark plugs and check whatever else could cause the problem. This time they found that the harmonic balancer bolt was loose. Strangely, they did not charge me to change the plugs and tighten the bolt. Sounds like the bolt was not tightened properly back when they changed the timing belt.
Does anyone know if there is a chance that something might have been damaged by not tightening the harmonic balancer bolt properly? It seems to me that the Toyota dealer might be trying to hide someting since they did not charge me for the service. Should I have another mechanic inspect the harmonic balancer?