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'04 Toyota Corolla S "overthrottling"?

Every so often, my manual transmission Corolla will “overthrottle” during acceleration, especially shifting into 2nd and 3rd gears (and sometimes even 4th), i.e., the engine will race above the usual RPMs associated with each gear, just for a bit. This however, isn’t consistent. I still need to check if the engine air filter is dirty, which I suspect could be a part of the issue. The vehicle has ca. 124,975mi, and only started exhibiting this problem 2-3 months ago, and only in 2nd gear. Again, this issue is very intermittent, and sometimes I can go a week or two without any incidents at all. The regular maintenance (oil changes, cooling system maintenance, etc.) has been faithfully performed according the manufacturer’s specifications. Has anyone experienced anything like this?

Probably a good throttle body cleaning to clear any deposits causing the throttle to hang would be helpful. It’s helped just about every sticky throttle condition I’ve come across.

It has to do with one of the smog controls on the engine. Under certain conditions, it will keep the throttle open to reduce emissions. Some vehicles are worse about this that others.

Have you ever had a car with a clutch that was starting to slip? Do you mean that with your foot off the clutch the engine rpms go up but the car does not accelerate normally?

As @arsemaster says, if the rpm goes up but the car doesn’t seem to be accelerating consistent with the engine speed, suspect a slipping clutch. It wouldn’t be uncommon to notice this when accelerating in 2n’d gear as the first symtom, as you get a lot of torque in 2nd gear.

I’m a master of arse now?

Maybe I mis-understood, do the RPMs continue to climb when you shift while you have the clutch pushed in and have let off the throttle? This was my interpretation. Or do the RPMs climb higher than normal while the clutch is out and you are accelerating, as in slipping clutch?

The clutch does not slip. This issue only concerns acceleration.

My apologies for the typo @asemaster!