Recently, the idle in my 1994 Cadillac DeVille stays up high. This happens when slowing to a stop. Once I stop, the idle drops down to normal. It’s like the gas pedal is sticking. I checked the pedal, but it does not appear to be sticking, and nothing is in the way to cause it to stick.
I called a shop about the issue. They said I should bring it in but did not have any idea what would cause the trouble.
The check engine light is not on. I looked under the hood to see whether anything was out of the ordinary, such as a mouse nest, but everything looks fine. Do you have any ideas? – J.T., email
Apparently, your car does not like to slow down for stops. Be this as it may, the trouble might be caused by a dirty throttle body or air flow sensor. It’s also possible there is a fault in the throttle position sensor or idle motor.
Cleaning the throttle body and mass air flow sensor might resolve the trouble. If tests determine a fault in the idle motor or throttle position sensor, replacing the failed part is the cure.
It’s also possible a condition known as sail on is impairing deceleration. If this is true, a technician can trigger an idle relearn process for the computer and throttle position sensor
Couple this with a few drive cycles, and the idle speed should return to normal.
I have a 2013 Ford F-250 with a 6.2-liter engine that is driving me up a wall. At highway speed, I feel a surging. It’s as if the engine is skipping every once in a while. It’s constant on every highway trip. It happens around 1,400 to 1,800 rpms. If the engine speed is below or above that threshold, I don’t feel it.
I have taken the truck to my shop for this issue. There are no codes. They can’t find anything wrong. They have tuned the engine, tested the fuel pump and done other tests. Even driving it for two days has not given them a clue as to why this happens.
My truck has 58,000 miles. I’ve owned it since it was new. Do you have any ideas? – W.D., email
I wish I had more information about your truck, but I do have some ideas. If your truck is a flex fuel vehicle, ask your technician to consider another test of the fuel pump. It might be a two-speed pump. It’s possible it is not delivering the correct pressure at the RPM you describe on the low speed of the pump. It might be kicking into high speed due to a lack of pressure, resulting in the surge you feel. Ask him to consider this idea.
Let me know if he finds this useful. If so, a new pump should cure the issue.
Additionally, it is possible that if your technician performs a computer relearn procedure, the issue will be resolved.
I have a 2010 Porsche Panamera S I hope you can share some thoughts. Once in a while, the suspension warning light turns on. The light only comes on in sport mode. Just before that happens, I hear an unusual noise, then it stops. As I continue on, the light goes off and all is well.
I went to a shop that specializes in foreign cars. A mechanic ran a test and found codes for the sport mode. The trouble is he does not know what causes the issue because everything checks fine. He thinks it might be caused by a bad compressor, but tests show it’s fine. He also thinks it might be caused by a sticky level sensor because I don’t drive the vehicle much.
My car has 11,000 miles. Do you have any suggestions? – D.R., email
Because you hear an unusual sound about the time the warning light turns on, odds are the suspension air compressor motor is failing. Ask your technician to consider running the compressor several times in a row. More than likely, he will find it draws too much electrical power. It’s also possible it might start making noise after repeated runs. He also might consider connecting a pressure gauge to it to determine whether output is sufficient.
I’m a Volkswagen owner of 30-plus years. I’ve owned two Cabriolets, a Passat and three Beetle convertibles. I can’t believe P.O. isn’t taking his car directly to a VW dealer for maintenance and repairs. In this case, the VW specialists would have diagnosed the problem the first time, made the appropriate repair and stood behind their work.
By saving a few bucks by going to tune-up and muffler shop, he got hosed by dealing with amateurs who will replace whatever you ask them to, hand you a bill and hope you forget where the repair was made when a breakdown happens again.
The average mechanic at a VW dealer has 15 to 25 years of experience, is trained on VW repair and has an entire service department he can consult with on an unusual problem. The average mechanic at a Jiffy Lube, Midas or AutoZone has less than three years of experience and is working on so many brands and models, each one may be his first on that particular make and model. What do you think? – T.B., Golden Valley, Minnesota
I hope P.O. is reading the column today. Perhaps he will take your experience to heart and have his vehicle checked by a Volkswagen dealership technician the next time his vehicle is giving him trouble. He was having trouble with a catalytic converter that apparently was failing due to issues in the engine, such as an overabundance of raw fuel contaminating it. Certainly a dealership technician might find a problem such as leaking fuel injectors or other conditions that might cause the trouble.
In a recent column, M.R. had trouble with a fuel leak in his 1999 Ford E-350 with a 7.3L Power Stroke diesel. There are some characteristic issues most likely causing the intermittent fuel leak. First, the extreme cold did most likely have an effect on the fuel system, although just the beginning of an issue is sure to pop-up again. The valley between the cylinder heads contains most of the fuel delivery system and drains to the area of the starter. There are rubber sleeve seals where the fuel distribution manifold attaches to the cylinder head, o-rings on the water drain valve and rubber fuel lines between the fuel pump and the filter housing that all are usual suspects for leaks. Visual and physical access to the site is an issue. A good inspection camera or removal of the intake plumbing and turbocharger may be necessary to see traces of this phantom issue as well as execute repairs. Can you pass this on? – M.P., Woodstock
Thanks for your letter. Yes indeed. Hopefully M.R. is checking out the column today. The configuration of the valley in this diesel and in many gasoline powered vehicles might conceal leaks, including fuel, oil and coolant. While many shops do not have inspection cameras to probe cavities such as the valley, it should be an essential tool in all shops. It saves diagnostic time and saves customers bucks. Without the tool, a technician could only speculate with a reasonable degree of automotive certainty there is a leak under the intake plenum in the deep darkness of the valley.
I have a 1999 Ford F-150 truck with 207,000 miles and a 5.4 engine. Two years ago, I had a problem with the engine not idling. I replaced the idle control valve with an aftermarket part. Recently, upon the first start of the day, my truck starts up fine, but at times the idle goes high. After driving and sitting for a few seconds, it starts right up, but if it sits for a while, it is slow to start. At times, it starts, then the RPMs drop very low, and then it recovers but there is a strong burned gas smell. Do you think the idle control is bad again? – T.E., email
Yes. This condition might be caused by a failing idle control. It’s also possible an issue such as this is caused by much more, but it might be caused by a sticking exhaust gas recirculation valve or perhaps a failing mass air flow sensor. Tests should be performed to determine stored or pending malfunction codes. Tests of the individual parts should be done as well, especially if codes warrant investigation of these parts.
Since it appears you replaced the idle control, if you are considering taking on the task again, consider installation of an original equipment part if it is available. It might last much longer than the aftermarket part.
• 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 drgizmo@drgizmo.ws. Information is available on his website, http://drgizmo89.blogspot.com.