Hello, and thank you for letting us help you with your automotive question. If the problem occurs mostly at low RPM then he needs to clean out the throttle body and check the vehicles fuel pressure. If the throttle body is dirty then it can choke the engine of air. If it is fine then the fuel pressure may be low due to a failing fuel pump. Do you know if the check engine light is coming on?
Thank you for your response.Yes, CEL is coming on. Throttle body was cleaned by mechanic on Friday 7/27 during diagnostic process. Idle Air Control Valve was replaced yesterday. Vehicle ran fine for several hours in varying conditions, mostly highway until traveling over rough terrain and likely low engine speeds. Is there a way to DIY check fuel pressure? She and the Subaru are several hours from a mechanic. Waiting on a code in a few hours when ranger station equipment building opens up.
My daughter ran a OBDII and got a P1507, Limp mode, which is typically remedied by IACV replacement. She's cleared the code and is taking the car for a drive recording the types of operation: engine rpm, speed, throttle positionat low and high rpms. waiting on test drive results
Okay. Thank you for the reply. To check the fuel pressure she would need a fuel pressure gauge. As for right now I would make sure that there are no vacuum hoses leaking and that the air intake tube from the air filter to the engine is secure. If it is loose then this will happen. If it is fine then the throttle plate may be worn in the cylinder or the mass air flow meter may be faulty.