Avensis Won't Rev Over 3500 Rpm

[Avensis luna 03]

Hi all.

I have a 1999 Avensis 1.6 petrol 4AFE engine. 140,000 miles on the clock.

In the past few weeks, when running at normal operating temperature, the engine won't rev past about 3,500 rpm. I say "about" as sometimes it could max out at 3,000 rpm, sometimes at 4,000 rpm.

The engine runs normally up to the time it reaches normal operating temp. No problem red-lining it and no misfiring.

When hot, engine speed will increase without any problem up to the 3,500 rpm or so, but then stutters just like the rev limiter is reached. On occasion, the Engine Management Light will come on momentarily but no fault code is stored, so that's no help.

The Spark plug leads and the O2 sensor were replaced about 30,000 miles ago. Car is in great shape, and runs perfectly, besides.

Any ideas? Any help would be very much appreciated and Thanks in advance.