Hilux power loss rough running

Greetings! Your symptoms indeed point towards a potential intake system issue. The loud hissing you hear may very well be air escaping due to a faulty seal or a malfunctioning control mechanism within the intake manifold. The intake manifold's job is to distribute air evenly to each cylinder. If the airflow is disrupted, it will lead to reduced power, rough running, and increased fuel consumption, as you've described. I once had a similar experience with my old BMW 320d; it turned out to be a defective swirl flap actuator motor. This motor controls flaps inside the intake manifold, optimizing airflow at different engine speeds. If these flaps aren't working correctly – like if the actuator motor is broken – it can cause the exact symptoms you're experiencing.

Interesting. What exactly do these 'swirl flaps' do, and could that be the cause on my Hilux?

Ah, allow me to elaborate. Swirl flaps are small valves within the intake manifold designed to improve the combustion process, particularly at lower engine speeds. By partially closing these flaps, the incoming air is forced to swirl, creating a more homogenous air-fuel mixture. This leads to better combustion, reduced emissions, and improved fuel economy. However, if the intake manifold flap control malfunctions – perhaps due to a defective switch, actuator, or linkage – the flaps may not open or close at the appropriate times, disrupting airflow and causing the symptoms you are experiencing. Given your Hilux's symptoms and mileage, it is quite plausible that you are experiencing a similar issue. It would be prudent to consult a qualified technician for a thorough diagnosis. They will likely use a diagnostic scan tool to check for fault codes related to the intake manifold or airflow control system. Do not attempt repairs yourself unless you possess the requisite expertise and equipment. For me the whole repair ended up at 465€

Thanks for the detailed explanation! I'll take it to a workshop and get them to check the intake manifold flap control.