Dear Jim,

I drive a 1995 Mercury Sable LS (3.8L, V6) that still runs well after 73,000 miles. Recently, though, I noticed that the engine vibrates a lot whenever I'm stopped at a red light.

The shaking lessens if I put the car in neutral, and it goes away when I start moving again.

One mechanic told me I need a complete tune-up: spark plugs, wires, rotors, etc., while another guy is telling me to change the engine mounts. Which one do you think is right?

Do I need both of these jobs done?

Also, my ABS light is on most of the time now, although the brakes seem fine. Could that be related to this problem somehow?

-- Jim Vargas

Let's talk brakes first, bro, because that's by far the most important thing to maintain on any vehicle. I'll bet that the indicator light for your anti-lock braking system (ABS) is telling you about a bad ABS sensor on of your wheels. This generally won't affect the car's stopping power, but if you go into a real skid, the wheel with the bad sensor will simply lock up.

That's not so horrible, but you do need to get it fixed when you can -- probably for around $150.

Your vibrating engine is a separate issue. Honestly, it sounds like the mechanic who suggested a full tune-up was trying to sell you a bill of goods.

No matter what anyone tells you, new spark plugs don't typically create a noticeable improvement in the way your engine runs. Besides, the vibration you're getting while idling is a big clue. If you had a bad plug, you'd notice the engine misfiring at high RPMs, not low.

Anyway, the guy who's talking about bad motor mounts is probably right. I explained how to diagnose this in a column several months back, but I've been asked about mount problems several times lately, so here's a recap: Open the hood, step down hard on the brake, and rev the engine to about 1,500 RPM with the car in drive. If you see the engine lift up, you've got a bad left-side motor mount. To check the right side, do the same thing with the car in reverse.

If either or both mounts are bad, brother, then you've found the reason for that vibration.

Tip of the Week

If you do notice the engine misfiring at higher RPMs, drivers, get those plugs checked soon. A speedy fix can save your expensive catalytic converter from serious damage.

Buffalo Jim, owner of Allstate Auto & Marine Repair in Las Vegas, writes a weekly column. Send your automotive questions to him at buffalojim@lasvegasniftynickel.com. If Jim picks your question to answer in Nuts & Bolts, you'll also be the proud recipient of a deck of official Buffalo Jim playing cards, presented in a classy, tin box bearing his hairy image.