I’ve got a bit of an issue which will probably be difficult to explain.

Particularly when the car is in 4th gear at motorway speeds, when I press the throttle to accelerate (without shifting down, so the car stays in 4th) the revs rise slightly by about 700 rpm and then fall back to where they were.

The car still accelerates, but it’s quite a noticeable rise and then fall in revs.

It’s almost like pressing the throttle and then quickly easing off the way that the revs and sound rise and then fall – but I’ve got my foot in the same position.

Hopefully you’ll understand what I mean. The car hasn’t always done this and it doesn’t always do it now, but it’s getting more common.

At my last service, my mechanic said the throttle body needed a service. Could this problem be related to the throttle body?

Any help would be appreciated.

im not too sure if this is what you mean, but for example, my car was acting up a bit in the same way, at cruise, when your just feathering the trottle, it was like as if the ignition was suddenly turned off for a couple of seconds then turned back on. if this is what you mean, then the likely cause is the TPS (throttle positioning sensor). i replaced mine the other day, and the car is perfect now

From your description, the car is simply disengaging the Torque converter clutch (which locks the converter solid so there is no slip)...once the car then gains some speed, the TCC will engage again making the converter solid and the revs will drop down again.

If these rev changes occur smoothly without any jolts then it's just the torque converter bits doing their thing.

At least with the third gen the car gives you some feedback on the tachometer what the engine and gearbox are doing. In my TS V6 auto, I can take off at 2,000 rpm and the tacho just sits there at that reading as the car accelerates up to about 80 kph. I had to get used to the third gen way of doing things, the tacho actually moves as it changes gear! Especially first!

From your description, the car is simply disengaging the Torque converter clutch (which locks the converter solid so there is no slip)...once the car then gains some speed, the TCC will engage again making the converter solid and the revs will drop down again.

At anything over 1500rpm, a 700rpm change wouldn't be due to the torque converter lockup - torque converter lockup would only account for 200rpm at most (over 2000rpm, 100rpm at most).

If the engine is actually changing by 700rpm without the speed changing much, it seems more likely that something is actually triggering a downshift.

At anything over 1500rpm, a 700rpm change wouldn't be due to the torque converter lockup - torque converter lockup would only account for 200rpm at most (over 2000rpm, 100rpm at most).

If the engine is actually changing by 700rpm without the speed changing much, it seems more likely that something is actually triggering a downshift.

That's a good point - but the OP says it stays in 4th - no downshift. Found the following at a site:
The Transmission/transaxle Converter Clutch (TCC) system has different operating characteristics than an automatic transmission without TCC. If the driver complains of a "chuggle" or "surge" condition, the car should be road tested and compared to a similar car to see if a real problem exists. Another TCC complaint may be a downshift felt when going up a grade, especially with cruise control. This may not be a downshift, but a clutch disengagement due to the change in TPS to maintain cruising speed.

Could also be a mis-behaving throttle position sensor (TPS).

Thanks for the replies everyone.

I’m not sure if it’s done this the whole time I’ve had the car and if I’m just noticing it now, or if it’s an issue that has just emerged.

Like I said, it doesn’t do it all the time. I jumped in the car this morning to try and video the issue but it didn’t do it at all.

Yet sometimes it will surge quite a bit (up to 700rpm) and other times it’s only just noticeable.