DR. Gizmo Part IV

January 3, 2010

"Dr. Gizmo"

By Phil Arendt

Mechanical Problem Raises Engine Idle Speed

Question 1
My 2002 Hyundai Santa Fe with a 6-cylinder engine has a high idle and the check engine light is on.  I took the vehicle to my local mechanic who replaced the throttle position part.  The car ran better after the repair, but the engine still idles too fast and the check engine light turned back on.

I returned to the repair shop, but the mechanic cant find the trouble.  He did some tests that tell him the engine idle is too high but he does not know the cause.  He says that the trouble might be in the computer, but he doesnt want to replace it unless he knows for sure that it is the problem.  He says that the only trouble code in the computer is a high idle code and everything else is fine. 

Whats wrong?  B.R., email

Answer 1

Something out of the ordinary is causing this condition and needs attention. The code that tells your mechanic that the idle is too high is a clue he should contemplate.  He knows all the sensors are functioning correctly because there are no malfunction trouble codes indicating a circuit or sensor has a fault.  Since this is the case, ask him to consider a fault that is mechanical instead of electrical.  He may find that the gas pedal or one of the throttle cables is binding.  Maybe a throttle cable is not properly secured.  Maybe there is a problem with a cruise control cable. Once he looks into a possible mechanical fault, he likely will find the cause of this condition and make a lasting repair.

Symptom Points Toward Fuel Pump   

Question 2

Recently, I purchased a used 2002 Saturn Vue with 26,000 miles.  It looks and drives like new.  However, every once in a while I hear a buzzing sound in the rear.  I hear the sound every day as I drive to and from work.  My office is 18 miles away and I hear the buzzing sound once or twice during the drive.  The private party that sold the vehicle to me told me about the sound before I purchased it.  He said he did not know what causes the noise.

I took the vehicle to my local mechanic.  He drove it several times during the course of a day and to and from his home.  The buzzing noise never surfaced.  He said it is possible that the fuel pump is making the sound, but he will not replace it until he actually hears the noise.

I am concerned the fuel pump is making the sound.  I am worried it will fail and strand me on the road.  What do you think is causing the buzzing sound? L.T., email.

Answer 2

I understand your concern.  No one wants to be stranded on the side of the road.  A failed fuel pump could certainly stall your vehicle.  Be this as it may intermittent noises are difficult to diagnose.  Without hearing the sound, your technician can only guess as to what might be causing the noise.  Despite this, there is hope.

Your vehicle has two fuel pumps a primary and secondary pump.  A check of factory technical service bulletins found one bulletin that might shed some light on the cause of the sound.  Factory bulletin number 03-06-01-007 refers to a noise similar to your description.  It states that the secondary fuel pump fuel pressure regulator associated with the secondary fuel pump might cause a buzzing sound.

Ask your technician to look up the bulletin in his technical library.  If he has the proper equipment, he can perform tests in his shop that cycle the fuel pump.  If it makes noise during tests, he can verify the condition.  If the fuel pressure regulator buzzes, he has pinpointed the source of the noise.  If indeed the pressure regulator is the source of the buzzing, according to the technical service bulletin replacing the secondary fuel pump module will end your concerns.

Vehicle Fails Emission Test Due To Fuel Vapor Leak 

Question 3

The check engine light is on in my 2000 Chevrolet Blazer with a 4.3-liter V-6 engine.  My truck has 147,000 miles.  It runs as good as new but it failed the state exhaust emissions test because the light is on.

After the smog test, I took the truck to an auto supply store where a person ran tests on the computer.  His tester found code po442.  He said that the code indicates a leaky gas tank.  When I got home, I checked the gas tank for leaks.  It is rusty, but I dont see any leaks.  Also, I dont smell any gasoline fumes.

What is causing the check engine light to turn on?  A.T.O., email.

Answer 3

The code that the auto parts store person read from his test equipment indicates a small evaporative emissions leak.  Your vehicle is designed to prevent gasoline vapors from escaping into the air.  The fuel system is sealed.  Sometimes when something such as a gas cap fails, sensors in the fuel system send a signal to the powertrain computer that there is a vaporous leak and that the fuel system is no longer sealed.  In turn, the powertrain computer illuminates the check engine light.  Sometimes the check engine light turns on when liquid fuel drips from a leak, but it also turns on when fuel vapors escape.  Since the sensors are extremely sensitive, your nose may not detect any fuel odor at all.

Fixing the trouble might be difficult.  Small vapor leaks are difficult to detect.  Technicians use specialized equipment to locate small leaks.  Troubleshooting a vapor leak can be a time-consuming process that racks up labor charges when a failed $3 rubber seal is the source of the condition.  Let us hope that it does not take long for a technician to pinpoint the leak in your truck.

Its possible a faulty gas cap, failed seal, solenoid, purge valve, fuel hose or rusted fuel tank filler neck is the source of a vapor leak.  A contaminated canister can trigger the engine light, too.  A technician needs to focus on the entire system in order to find the source of the leak.  Once he or she locates it, the repair might take a few minutes.

ABS Warning Light Illuminates In Cold Weather

Question 4

Intermittently, the anti-lock brake warning light turns on in my 2002 Chevrolet Tahoe.  Last winter the light turned on.  When the light is on as I apply the brakes the brake pedal sinks and it feels like truck will not stop.  After I drive a few minutes, the brakes begin to work normally.  This only happens in the morning for the first few minutes of driving on cold days.  During the summer, the light does not turn on and the brakes feel and work fine.  Now that cold weather has returned, the brakes are acting up. 

Whats the problem?  T.L., email

Answer 4

This condition is serious.  Take the vehicle to a repair shop to have the problem corrected before you are involved in a collision.  Leave it overnight so a technician can experience the symptoms in the morning when the truck is cold.

The trouble might be the result of failed wheel speed sensors.  Maybe corrosion or dirt is affecting the air gap between the sensors and tone ring.  Maybe an electrical connection is suffering from moisture or corrosion.

Ask a technician to consider my suggestions when you take your truck to a repair shop.  Dont delay.

Engine Lies Dormant When Ignition Is Turned 

Question 5

Occasionally, my 2005 Chevrolet Colorado with a 3.5-liter engine will not start.  This can happen the first thing in the morning on the initial start of the day or it may happen after I have driven an hour, stop and return to the truck.  When I turn the key to start the engine, nothing happens.  The lights on the dash turn on, but the engine does not make a sound.  If I wait ten minutes or so and try again, the engine usually jumps to life and starts as though nothing is wrong.

I spoke to my local mechanic.  He says he wont be able to determine the cause of the trouble unless the engine wont start for him.  I'm concerned that eventually I will be stranded.  Whats the problem?  F., email

Answer 5

Your mechanic has a valid point.  He could only guess why the engine does not start.  This would result in needless installation of parts without fixing the trouble.  This could cost you a bundle.

You might ask your mechanic to check the battery cables for corrosion and security.  If corrosion has impaired the cables, he should remove them from the battery and remove all corrosion from the battery terminals and cable ends. 

He might consider checking connections at the starter motor for security and corrosion.  He may find a loose connection that needs tightening or other conditions that impair operation. 

Performing these checks will at least rule out possible causes and he may find the source of the trouble.  If so, a simple turn of a nut might be the fix.

Its also possible a scan of computers might find a problem such as a faulty ignition switch or maybe there is a problem in the theft deterrent system.  If so, he may be able to cure the trouble without having to do guess work.

Cost Of Repair Exceeds Vehicle Market Value

Question 6

Recently, I took my 1993 Chevrolet Caprice for a state emissions test.  It failed.  My car has a 5.0-liter V-8 engine and 194,000 miles.  It has never failed me since the day I purchased it in 1993.  Because it failed tests, I took it to my favorite repair shop.  A very reliable mechanic checked it over.  He determined that the engine is suffering from excessive wear.  He said he could repair the trouble, but to do so will cost a lot more than the car is worth.

I love my car.  I have taken great care of it all of these years.  There has never been any trouble with the transmission or anything.  Everything works great.  Other than the worn engine, it drives and looks almost like new.  There is nothing made today that is comparable to my car.

Should I fix her up? S.K., email

Answer 6

The market value of a car similar to yours in excellent condition without engine problems is probably close to $2,300.  To repair the engine could easily top that.  In addition to this, no one can predict what will happen to your car in the future.  The trouble is that overhauling or replacing the engine might just be the beginning of a long list of repairs.  The transmission could fail at any time.  There may be issues in the suspension such as worn bushings and ball joints.  The springs that support the vehicle more than likely need replacement.  Brake hydraulic lines more than likely need replacement due to corrosion.  The air conditioning system may fail. 

My vote is to say good-bye to your long time friend before it becomes a never-ending cycle of expensive repairs.  If you decide to part with your car, you may be surprised at what a new Impala has to offer.  Not only is it similar in many respects to your present vehicle, but the fuel economy it achieves surpasses your present vehicle by a long shot.

Thanks for all of your great questions.  Dr. Gizmo cant wait to answer more.

Phil Arendt is a columnist, consultant and A.S.E.-Certified Master Technician.  Readers may send questions to Dr. Gizmo at P.O. Box 548, Cary, IL. 60013 or e-mail address [email protected]  12/14/2009 ® DR. GIZMO © 1989-2009

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