Intermittent RPM drop

[buckycasuals]

Evening all,

Recently I've been chasing intermittent RPM drop on Honda Jazz 2011 CVT.
When stopped at a red light, sudden vibration  starts building up for a few sec until the RPM drops from 700-500. But it usually goes to normal immediately. It will happen you stop again at a red light.

RPM does drop at night when headlight is switched on, but it doesn't cause vibration, probably because the engine compensates for it. Garage tested alternator and battery, but all seems good.

My garage has adviced me to switch to E5 fuel as there is no CEL to help him diagnose the problem.

I'm not sure if E10 fuel could cause that.

Thanks

[Keekster71]

When was the last time the plugs were changed?

I think a full diagnostic, with the garage checking the live data whilst the engine is running and the car driving would be a good start, to see if there are any intermittent faults, e.g. dodgy coil pack or plug.

E5 fuel wont make any difference.

Another thought, does it do when the air con is off?

[buckycasuals]

The plugs were changed December last year with Bosch Iridium. Something that have developed recently is a vibration on the seat that starts building up after few secs when stopped followed by a sudden RPM dip.

It happen when AC is off. But then it idles higher when AC is switched on. But the RPM drop is still there if you look closely.

I've already ran Techron PEA cleaner, Liquimoly cleaner in the tank and they made no difference.

[Marco1979]

It might be a combination of things, e.g. the computer adjusting rpm to minimize CO and an air conditioning pump that does not run smoothly any more.
Maybe you could check the serpentine belt and how difficult it is to turn the air conditioning pump (I do not know how; a mechanic should know)?

[buckycasuals]

Sorry I meant it happens when the AC is off. It doesn't happen when AC is on but the RPM drop or dip is still there if you watch the RPM closely.