Runs fast when I turn it on then goes back to normal running speed

post a photo with finger pointing to object humming.
we can not ever guess this.
there are 3000 parts on the car, and ive seen like near each make noise moving fast, 1 time the other.
1: check all fuses
2: makes sure battery voltage is at 12.6vdc rested, key on still close to 12.6vdc , still makes hum.?
my guess is the battery is drained but no proof, im not there use my voltmeter.

You have to change your clutch kit. I just had this issue and after changing it it runs smooth again.
Just to confirm, you shift gear up, your engine roars (goes up to 4000 or more RPM) but doesn't gain speed until few seconds later after the RPM is back to normal.
If so that's the clutch plate causing the issue.
Please rate

try changing speed control sensor

TPS (Throttle posision sensor) would be my guess

jack car just enough to take the weight off the road wheel, then using a tyre iron, see if theres any movement in any bushes,only try this on the flat with bricks under the chassis frame just in case....

MOST of the hums after a while come from the diff as the back axle does the driving and almost all its life runs the same way except when going in reverse ,is the rear diff meshing and worn on both the crownwheel and the pinion and the humming gets slightly louder the faster you go and almost goes when almost stopped and this can also be the slight vibration you get so get the diff oil drained and refilled and check if there is any metal in the oil when drained if so thats your problem But it will last for years like that..Let me know how you get on RON

this may be something you might check ? the fact that the noise sounds like humming? on rapid decelleration from speed ? as you release throttle from speed downhill the turbo revs drop off and pressured air is reduced into manifold ok ? but the engine speed/rotation is then driven by the drive from the roadwheels/transmission therefor the engine is vacuum caused by induction into manifold is still on increase but due to possible induction hose from turbo to manifold ? this hose may? be collapsing /sucking together thus creating air restriction to engine if this does happen ? then the symptom of labouring and sound of humming you describe may be what is happening? for your info the cause of over rev of engine especially on decelleration from high speed could cause the pistons to catch ip with the valves and bend them? this is a danger to avoid hope this helps?

no -not normal
take it to an accredited service center for a proper diagnosis and quote

might be engine running hot check fan..