Rough Idle Shaking on SUV is Rattling the Owner

October 30, 2010/Steve Tackett

MOTOR MATTERS ASK THE AUTO DOCTOR BY JUNIOR DAMATO

Dear Doctor: I own a 2002 Oldsmobile Bravada. I have been experiencing a very rough idle. It is so bad at times that it shakes the floorboard and rear window. I had a service and tune-up, but the mechanics tell me they were not able to duplicate the problem. Any idea where to start on finding a cause? Donna
Dear Donna: An engine roughness issue is usually caused from either an ignition misfire or an EGR valve that is stuck partly open, which is common on this engine. Another possibility is an intermittent vacuum leak.
Dear Doctor: I own a 2003 Buick LeSabre that I purchased new. It has had an ongoing problem with the battery going dead after a few days if I let it sit and don’t start it. I have replaced the battery and some electrical parts over the years. My son has to come over and use a jumper to start the car for me. What do you suggest? Florence
Dear Florence: The first step is to find a qualified technician. Call your local AAA office, even if you are not a AAA member, and ask for a AAA-Approved repair shop in your area. There is battery voltage drain when the key is shut off. Over the years I have seen hood, truck and glove box lights, power seat and door lock issues. Under the hood, a faulty alternator can draw current when the engine is off and still recharge the battery when the engine is running. These problems are not too hard to find. The technician should also check on the Identifix and Alldata web sites to view information.
Dear Doctor: I own a 1997 Toyota Avalon with 118,000 miles. The “check engine” light comes on constantly and I’ve had it fixed many times. Now I’m having the shop shut the light off, drive it for two days and then go for my smog check before the light comes back on. What would cause the problem? Linda
Dear Linda: The mechanic cannot just shut the light off and you then go for the smog test. There are many reasons for a “check engine” light to go on. In your case, it is a two-drive cycle fault. This means the computer has to see the same fault on the second-drive cycle. A drive cycle is when the car is driven under certain conditions for a certain amount of miles and highway speeds. Each car manufacturer has different driving conditions to set the computer monitors during the drive cycle.
Dear Doctor: I own a 2007 Ford Mustang GT with the five-speed manual transmission.

I want to either add performance equipment to it or upgrade by purchasing the new 2011 Mustang GT. Have you driven the new Mustang with an automatic transmission? Is the 5.0-liter that much better than my 4.6L? Andrew
Dear Andrew: I drove the new 2011 Mustang 5.0L. With the six-speed automatic and 412 horsepower, the new Mustang has more power and performance than you would believe. A few add-on performance parts right from Ford will make it even better if you want. Ford has done it right with this car’s driveline package.
Dear Doctor: I have a 1998 Chevy Corvette with the LS1 5.7L engine, automatic transmission, traction control and active handling. The ECTBM module is bad. My mechanic can’t find a replacement and GM has discontinued it and we can’t find a rebuilder. Any advice? Bruce
Dear Bruce: We use a company called BBA remanufacturing out of Taunton, Mass. You can also try Mid America Corvette. There are also many salvage yards that specialize in Corvette parts.
Dear Doctor: I have my 2008 Jeep Wrangler serviced at the dealership. I only use the 4WD in the snow. Every year, or 12,000 miles, the service advisor recommends service on the front/rear differentials. Since I don’t use the 4WD that much, why do I have to service the differentials? Same situation with the throttle body. My Wrangler now has 25,000 miles and I spent about $1,400 in two years just to have these items serviced. Is it worth it? Sam
Dear Sam: Your Jeep requires maintenance that is listed in the manual. — Junior Damato, Motor Matters

Junior Damato is an ASE-certified Master Technician.

E-mail questions to info@motormatters.biz

Copyright, Motor Matters, 2010

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