Car surging when start moving

[Ldjambazov]

This is my first tread and a question, although I have read lots of posts searching for information, and find this forum very helpful.

I recently bought a P5 2003 with 105K km. Did regular maintenance, breaks, spark plugs, thermostat, AUX input for the radio for bluetooth, first oxygen sensor, but had to do the non-fouler on the second one. One more thing, I drilled two small holes at the bottom of the wells behind the rear wheels. Water was accumulating into the wells, and until I figure out where it is coming from I decided to let it drain through these holes.

My real question is about the car trying to stall when I start to move it on first and second gear (manual trany). When I release the clutch (believe me I can drive manual) the car rpm go very low, then when I give more gas the car starts to surges and needs to reach certain rpm to be able to run smoother. So it is always kind of a jiggle between the clutch and the gas to be able to move without the annoying surging. This also happens on second gear, but not further. It is also more noticeable when the car is cold, but exists even if hot.
I will mention that the rpm on idle are perfect, there is no surging or rpm going up and down when idling. The surging is only when starting to move, and at lower than mid rpm.

Thanks for your help, and if you need more information I will post it promptly.

 

[sleepwalker]

Check your intake tube, between your mass air flow sensor and your throttle body, for cracks. They're notorious for ripping. The airbox is stationary and the engine shifts slightly when you accelerate, which pulls the tear open and allows unmetered air into the system.

 

[pcb]

 

[Ldjambazov]

Thanks, I checked the tube, it is fine, looks old but no visible cracks.

To me it looks like the throttle valve can't support low to medium rpm. I had a 1.8 VW, and on that car if the throttle valve looses "adaptation" it didn't know how much to open or close the valve, and was acting weird.
I am guessing similar thing on the Mazda, the engine doesn't get enough fuel at the low to medium rpm, and if I press the gas it starts to surge, not sure where the right fuel supply is. I have to rev it more to overcome the surging until it goes above 3000 rpm, but then I need to switch to second gear, where it does the same thing.
Another fact, when I pres the gas at still, and keep it at 1000-1500 rpm, it behaves normal, no surging.
One more, there were some codes related to the front oxygen sensor and the CAT, but I managed to get rid of them, fixes listed above.
Any other ideas, you can suggest anything, I will try it.
Thanks.