In MOT, sudden drop from 4000 RPM

[p993c4]

This week the exhaust emission was checked as part of the MOT. The emission was successfully measured at 4000 RPM. However, successfully after a few attempts, since the RPM dropped suddenly to idle after some time at 4000 RPM.

The sound of the motor was normal throughout the test and I haven't noticed anything odd in normal use. What is the RPM drop related to?

[Stealth 993]

Sounds like a dirty ICV, just pull it out & clean it.
It's kind of common on 95's to have a slightly rough idle.

[p993c4]

Thanks, the reason was dirty ICV!