My wife's Subaru has been at the shop for months. It runs rough and we don't know why.
Here's what he has done: Full oil change and filter replacement, Tire rotation, Brake inspection, cleaning and adjustment, leveling of all fluids, Full battery, starter and charging system check up (battery replaced), checked all lights and wiper blades, A/C system check, throttle pedal replacent (electronic pedal), Spark plug replacement, Fuel fuel pump replacement (complete pump assembly), Electronic EGR valve replacement, VVTI valves, cleaned and inspected, In line fuel pressure regulator bypassed to increase fuel pressure (fuel pressure regulator re installed),
This is all I have done to the vehicle. Fault still persists. Car has rough start and will idle poorly. Once warmed up engine will idle rough and only even out above 3500 rpms.
We live on a small Caribbean island and it's the European version of 2.0 gas engine.
It has 60000 miles and an automatic transmission.
There are numerous potential causes for your concern. Your vehicle has electronic throttle control, as you mentioned. In this system, a stepper motor integrated into the throttle body is used to control throttle position. The main inputs for throttle control include signals from the accelerator position sensor, which you already had replaced, and the throttle position sensor (integrated into the throttle body). A problem with the electronic throttle system could be cause of your concern. The issue could also be vacuum leak somewhere in the system. These are just two possibilities. For a definitive answer, the vehicle will need to be diagnosed firsthand by a professional, such as one from YourMechanic.
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