Rough idle could be a dirty problem

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By Junior Damato MOTOR MATTERS

Dear Auto Doctor: I own a 2004 BMW 325xi with a five-speed manual transmission. The problem is before the engine gets warm to set temperature the engine idles up and down and is not smooth when at a stop. Once the engine is warm it runs good. -David

Dear David: The first step is to check all sensor values. Then check for any possible vacuum leaks. Carbon buildup and dirty fuel injectors also could be a possibility. If the problem ends up being dirty injectors or carbon buildup, a professional service will be needed. There are no shelf chemicals from an auto store that would make a difference for this vehicle.

Dear Doctor: I own a 2002 Buick Rendezvous with 34,000 miles. Sometimes when I turn the key to start, nothing happens. I will put the shifter in neutral to start the engine. No one has been able to help me. What do you think? -Bree

Dear Bree: You will need to get the car to a good shop so that the tech can check the start position with a scan tool hooked up to it. The computer gets a signal from the transmission position selector. If the selector is out of range when in park then the starter will not engage. There also could be a voltage problem from the ignition switch to the starter motor. Whatever the fault, it will need to be checked by a qualified technician.

Dear Doctor: I live in California, and I own a 1992 Volkswagen Cabriolet. The air bag light is illuminated on the dash. My local mechanic and the VW dealer say they do not have the software to diagnose the problem on a 1992 car. I am out of resources. Can you help? -Jeff

Dear Jeff: There are a lot of good shops in California that work on older Volkswagens. Check the local AAA office and then go to those shops and ask whether they have access to Identifix. Between a good technician and Identifix, they can get to the root of the problem on your car.

Dear Doctor: I own a 1988 Mercedes-Benz 300E. On two occasions - only nine months apart - the engine died out; and when we went to restart the car, the starter did not engage to crank the engine over. On both occasions, the engine started and ran fine after one hour of sitting. I replaced a lot of parts including the fuel pump, regulator, battery and alternator, and many other parts. What are your thoughts? -Marty

Dear Marty: From your description, it sounds like a loss of 12-volt power in the electrical system. It could be anything from a poor ground connection to a bad connection at any electronic device. A good technician will need to check with a load test on all relays and connections in the system and hope he or she stumbles across the problem.

Dear Doctor: I live in Cape Coral, Fla., and own a 2007 Mercedes S Class with black exterior paint. I always hand wash my Benz. The problem I have is with water spots every time I wash. I have to dry the car after every wash and use a spray wax to get rid of the water spots. Do you know of a way to eliminate the water spots? -Ray

Dear Ray: Here in Massachusetts we have similar problems with water spotting. Hard water and chemically treated water and even some car wash soaps can cause this problem. I can tell you that I use a soap called Ice car wash by Turtle Wax. This cleaner got rid of the water-spotting problem for me. Another tip: When rinsing the soap off the car, remove the spray nozzle. This will eliminate air in the water stream. You should also chamois or towel dry the car.

Dear Doctor: We own a 2002 Cadillac Seville that had a blown head gasket. I decided to have the engine replaced for $6,100. The car has always been taken care of and never seen extreme hot or cold weather. Was there ever a recall on these faulty engines? -Roger

Dear Roger: To the best of my knowledge, blown engines such as yours were taken care of on a case-by-case basis for GM assistance. At this point with your vehicle being more than 6 years old, you would have to write to Cadillac for assistance.

• Junior Damato is an ASE-certified master technician. E-mail questions to info@motormatters.biz.