This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by theECU and so not compensated for causing rough running
as th eMAF signal is used by the transmisson to judge load and hence gearshifts, any fault with the signal will effect gearshift quality
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the enginerunning.
Check the hoseclips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.
The best way tolocate a leak is to have the engine running and warm and then spray lighter gas/propane around each joint in turn. If the engine rev's up you've found yourleak.
Now you mightthink that spraying lighter gas around a hot engine isn’t wise, however theflash /ignition point of gas is about 400°C so you need a naked flame or sparkto set it off and I’ve used this method for many years without incident.
Work your waythrough each possible joint one at a time and you should find it. I use aslightly flattened piece of brake pipe and some rubber hose from the can oflighter gas to provide a spraying 'wand' and allow a direct blast of gas intoeach area, especially those difficult to reach with large implements.
It’s also worthgetting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuelbeing delivered to the engine
Might also beworth checking the wiring and connector to the airflow meter for any signs ofcorrosion or damage. you can do a quick fault find if you unplug the meter andrun the engine without it.
if the enginecondition is the same then chances are the meter or the connection to it isfaulty
Air leaks are very temperature dependent as gaps can open or close up as things expand with heat,so the weather and engine temperature can effect them.
This leads them to be quite intermittent in the case of mild leaks
its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that thecleaner is one of the old fashioned, non Eco type that does not leave a residue
On no account touch the sensor wires with anything physical as they are extremely fragile