Hi 400E -

I could live with the vibration but... It didn't start until about a year ago. If is the vibration was constant and uniform, I'd consider it normal. But, it varies, has cycles, has highs & lows and similar to what you said, it starts a couple moments after stopping at a red light. I've contributed that part to the idle going from 600 to 700 RPMs will coming to a stop, and once the car is completely stopped the idle settles to 500 RPMs. Sometimes, giving the car just alittle more gas (while in gear and the brake is applied) and nudging the idle to 525/550 RPMs eliminates the vibration. This doesn't always work - but 60% or more - it works. I don't think this is the problem, it just hides it. At 525/550 RPMs there is too much resistance and you can hear it in the engine, etc.

The vibration is minor in the steering wheel, but it also causes noise in the cabin similar to back pressure in the exhaust - that probably gets to me the most. The car is due for its inspection, maybe the emissions test will shed some light on the culprit. The exhaust has the rotten-egg smell from time to time (e.g. the catalytic converter), but the shop said that occurs when the car burns rich. Techron is added every to 2k to 3k miles, so that's probably the cause. However, after 8 years and 96k miles, alittle exhaust work would not surprise me. Also, just about every sensor could be at fault.

Overall, I think it is a combination of factors - some mounts or bushing intended to absorb vibration need replacing, rehanging the exhaust is a good idea and finally the injectors probably need more than just a cleaning.

One final comment, this started after moving to Seattle from Dallas, TX. My first thought was the gas. It always gets premium from Chevron - however it 93 octane in Dallas, but only 92 Octane in Seattle. I've tried water removers in the gas, octane boosters, etc., No difference. So, I don't think it's the gas, but it's still an interesting coincidence.