My problem is with my wife's 2006 Taurus SE (3.0 litre with the 4-speed auto trans) that we've owned for just over a year. It had 37,000 km on it when I purchased it. It now has about 54,000 km.
Since we purchased the car, it has idled roughly, bouncing between 800-950 rpm. I've been to two dealerships. One performed a Terra Clean (including cleaning of fuel injectors, decarbonised the engine, clean cat convertors and oxygen sensors). Another dealer replaced the Idle Air Control (IAC). Neither helped with the erratic idling.
You know Ray, just today I was speaking with one of my colleagues and we both agreed that nothing can replace experience. As an apprentice mechanic, you can take part in the government mandatory training program and later, as a technician, commit to life-long-learning but until you experience "the things that make you go hmmm" you can spend a lot of time spinning your wheels trying to re-invent those wheels with a solution to a problem that someone has likely already tackled. This is one of those times.
Your Taurus is exhibiting the classic symptoms of a malfunctioning Exhaust Gas Recirculation (EGR) system. Savvy technicians will either know this through their experience, or as is the case with this day and age, search out this information on the internet. As a matter of fact, one of the most powerful tools a technician should have in his or her toolbox is a laptop with internet access. I'm sure this would have helped your repair shop dig deeper into the problem instead of applying a "light duty" process such as the typical chemical decarbonising. I hate to say it, but most of the time this doesn't work.
I have had personal experience with this exact problem and it is exhibited by many Ford EGR systems. Although the Ford design is very effective at measuring the amount of exhaust gas recirculation, which is needed by modern engine management standards, it is not without fault. Luckily this fault is not serious and only requires periodic maintenance.
The mechanical valve that actually controls the exhaust flow into the intake manifold for reburning and, more importantly, cooling of the combustion process, is not always to blame. Most of the time the problem lies with carbon build-up inside the port that allows for the recirculated exhaust gasses to enter the intake manifold. This port is located right behind the throttle body so the process of removing the throttle body and cleaning this passage is best left to an experienced technician. I mention this because it is extremely important that no carbon is allowed to enter the intake manifold, as these pieces can cause serious damage to the internal workings of the engine and support systems.
Ray, please feel free to take this information to your technician for consideration. They came close and were on the right track, but unfortunately the cleaning of this carbon problem requires elbow-grease, not a chemical treatment.
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