steering wheel vib while idling?

Well, this is the sort of problem that gives development engineers gray hair. The original U.S. Escort had, not long before launch, a steering wheel vibration of half an inch in amplitude at idle! It turned out to be a combination of engine mount design, the mass and stiffness of the steering wheel/column assembly, and structural vibration modes in the front end. It was dealt with by switching to a steel front bumper (from aluminum) and using that as a tuned-mass vibration absorber. But only in the automatic-transmission cars; the manuals were immune to the problem, as the loads at idle were slightly different. The '85-1/2 had a new engine mount system, redesigned front structure, and the radiator mounted on rubber as a tuned-mass absorber. Kind of a belt-and-suspenders approach to the problem.

Anyway, if this vibration is new, something has changed. I concur with the other poster that you might want to start replacing engine mounts, subframe bushings, and the like. After all, it's unlikely that the metal structure of your car has changed, and much more likely that rubber has gotten harder or is getting weaker. Oh, and if the radiator is on rubber mounts, check those, too :).

Hi, thanks for the reply...

The vibration is relatively new. The degree is not severe, as I've asked the dealer to check for it when I did an alignment and they claim they can't reproduce it. But I suspect they did not spend too much time on it, because it only occurs once the engine warms up.

Well, I do not know how to check or replace engine mounts, is it hard? (I am just comfortable opening the hood and check fluid levels, maybe if I really want to do it, replace engine oil and break pads). I did look at the engine from the top and nothing obvious seems lose.

So I guess I need to find a mechanic (dealer?) that I can trust to take a look at this. Anyone know of any in the SF Bay Area?

Thanks.

Raymond

I am not a car expert, what is the sympton of a rough engine? I do not notice any unusual noise from the engine, only that it doesn't seem to be as smooth at idle.

If it's the engine mount that's lose, how come the vibration goes away as soon as I hit the gas padel? Wouldn't it be more?

The Haye's Repair manual mention things like vacume leakage, fuel pressure, etc... could those be causing this problem? (maybe those have more severe symptons, but I am not really sure about those...)

Thanks.

Raymond

No, it wouldn't, thanks to the wonders of mechanical dynamics. To simplify outrageously, you have a tuning fork. If the natural vibration of the engine coincides with the resonant frequency of the tuning fork, it will vibrate. Any other frequency won't stimulate the vibration. This is especially true if it's an inline 4, which has an inherent imbalance at a frequency twice the RPM. There's a lot of careful tuning to isolate you from that vibration, and we're guessing than the tuning has changed so that the vibration is stimulating the steering wheel.

Well, that all falls under "rough engine". I don't know how to tell you if your engine is idling normally; I think you need to find a good mechanic who knows your model of cars. Out here in the wilderness, there are eccentrics that specialize in SAABs, Subarus, Volvo, and the like; you need to find the equivalent in the Bay area for your car.

In answer to your other query, probably the only way to diagnose engine mounts is to replace them and see what happens. If any of them has obviously deteriorated, then try replacing that one first. Doing, this, of course, is moderately involved, as you will have to support the engine's weight with a hoist or something, not to mention what you might have to remove just to get to the mounts. You probably have 3-5 mounts; one may involve a strut connecting the engine to the firewall, and that one might be in the form of a hydraulic damper that looks like a small shock absorber. If so, that damper might be worn. Again, a good mechanic who listens both to you and to the car would help.

Yarnell's Toyota/Datsun in Mountain View is a bit of a drive from SF but I found them to be excellent on my old celica. If you don't mind a bit of a drive give them a call and see if "Datsun" now officially means Nissan, since they were definitely specialists in a few makes including toyota and I don't think they worked on some brands, notably domestics.

Dave