M13a engine problem

Good evening at all... I'm Marco from italy... Unfortunately i have another problem with my 1.3 vvt 2005, m13a engine... Unfortunately, because the ecu don't help me... Zero errors detected... When the car is parked with the engine at minimum revolution, as i push a little bit the accelerator pedal, the engine "grumble" (i hope that google translate help me good with this word)... Over 1200/1500 rpm it run without any problem... Does someone have got a similar problem? I've thinked ignition coils, injectors, but without an error code, i'm not sure... And coils cost original a lot of money, injectors seems to be available only used. Noone have original new denso injectors on stock...

Many thanks for your precious help and advises.

Marco.

Just to clarify:

- When the engine is at idle speed (minimum revolution) and the car is not moving, it grumbles (runs rough, sounds like it's going to stall)

- There is NO check engine light on the dashboard/instrument cluster illuminated.

- The car is low on power/struggles when moving.

First and second point are correct, number 3 not at 100%... If i push the accelerator pedal and the engine go over 1200/1500 rpm, it run perfectly. The problem come out only at minimum rev, and not always. It seems as the engine run at 3 cylinders.

Start with a compression check. One cylinder could be low.