Blanking the EGR will not affect your MPG...putting your foot down will Check your air filter, make sure its clean.my egr is blanked off and ive removed all the vac pipes from the n18.
my mpg has dropped tho and i wanna put it all back to check but i cant cos i snapped one of the vac connections off the n18.
i can get hold of an n75 easier so wondered if that would be ok to use instead
I've tried it once, and it was working.I didn't read this correctly at first - I thought you had put an EGR delete in and blanked off the manifold. It was only when you started talking about two blanking plates that the penny dropped.
Did you clean the EGR out before disabling it? I'm not sure if it uses exhaust pressure but if it does it will now be clogged with no way to clean itself.
Have you double checked your vac lines? The only ones you have left should be; the pipe from the tandem to servo pipe which goes directly into the black side of the one way valve (having removed the T going to the N18) then onto an optional T leading to the reservoir if you want to retain it for output tests or otherwise directly to the N75. If you imagine them as tiers of a wedding cake it would feed the top tier. The middle one feeds the turbo actuator and the bottom goes into your airbox. That's it! there should be no other lines. I would leave the electrical connections attached to the three N valves though to prevent faults.
If this all checks out and the vac pipes are undamaged then I would suggest your fault lies elsewhere.
In answer to your original question, I wouldn't use a N75 to do the N18 job IMO - I don't think they work exactly the same.