Throttle surging while driving constant speed

[Lukeis]

Hi gurus

im currently on a lap of aus and have noticed this issue for the past two weeks.

trying to drive a constant highway speed but the revs keep surging despite being very constant on the accelerator or having cruise control on.

it’s quite annoying and happens with or without the caravan on the back. I can feel it slightly vibrate the car when the van is on before jumping back a gear. Without the van on you can hear it and slightly feel it but generally holds the same gear.

see video here
YouTube
have had a gearbox service a year ago. Is there anything I can check on the road?? Currently in streak bay in SA and about to go up the middle of aus so it’s making me a little nervous

[discorevy]

looks like torque converter clutch slip

[Lukeis]

looks like torque converter clutch slip

thanks, what’s the fix for that?

[Lukeis]

Should I consider resetting the adaptive learnings?

[gotaflat]

could be gbox, but suspect you may have other symptoms.

Tried in sport mode? does that happen then?

I had something similar may be not that noticeable until the end (I was blaming cruise control) - after a while i got fault..ended up being a turbo (consequently 2). Hope not

[Eric SDV6SE]

#1 torque converter slip. Get fluid level checked, if possible have a look at the fluid itself,should be relatively clear, not blackened. Others on here have said a tube of Dr.Tranny does help. A new TC may be required.

#2 valve body seals leaking, allowing fluid to bypass, forcing the tc to keep up. How does the shift feel? Harsh, clunks? Does it flare (i.e. rev up instantly before or after the shift? This needs a valve body rebuild.

#3 vacuum system, leak in intake tract, but these typically fault quite quickly and the car drops into restricted performance mode. Could be failing throttle body o ring.

#4 turbo, unlikley IMHO as this will drop the car into RP instantly, no surging.

[Lukeis]

Tested sport mode as follows

driving at around 100km hr

flick to sport mode:
car kicks back a gear, revs increase from circa 1500rpm to 2100rpm
no surging

use command shift to shift up a gear:
car drops back to circa 1500rpm and does not seem to surge

this is odd because I would have expected command shift 6th gear to be the same as auto 6th gear.

any help with this info?

[Eric SDV6SE]

Sports mode ups the line pressure in the valve body and subsequently in the tc. So S6 is not exactly the same as D6 in terms of line pressure. Std for it to shift down a gear when moving from D to S. The extra pressure may be enough to override tc slip for a while. If it is the tc slipping, it will eventually require a rebuild.

Do you know when the last transmission fluid change was? A flush and new fluid may help

[Lukeis]

Gday Eric

thanks for that info, TC rebuild sounds expensive.

would I assume like a clutch the longer you push it the worse the slip?
Will letting the problem exist flow onto other issues or is it safe to keep going for a while? I’m not sure what help I could get in this area of SA

[Eric SDV6SE]

Hi Lukeis,

Yes, provided the surging IS the tc slipping, its kinda like a mechanical clutch. The vanes / scoops inside wear, allowing fluid to bypass and so the engine side spins faster or slower than the transmission side. The transmission can keep up for a bit, or compensate to some degree depending on how much wear. Like any coupling it wears, especially if the fluid is dirty.

Can last 100km or 10000km, hard to tell. From what youve said theres little or no shudder,so sounds like youve caught it early. Id be trying to get it to a nearby workshop for a good check over.