I had to replace my original Bosch MAF sensor recently. Boy when it went bad car just would not run! I was amazed at how much it affected the running of the engine. It ran better with the sensor disconnected.
Anyways, I went for the newer design MicroTech sensor. The car seems to run ok, but now my tune is way off. I had it good before, at least I thought I did.
The WB shows stoic, when warmed up, but I know it is off. Engine doesnt seem to go into highway mode. And I know I had it all working.
Tonight was able to get laptop on the ECM, and first did an idle test, BLMs were at 108 and INT at 117. The O2 did seem to swing R/L, after closed loop, but was more on the rich side. I also noticed that learn control was disabled.......
After some time went by, I attempted to set it up and do a road test scan. I only got out my driveway and I lost connection with ECM from laptop. I couldnt get it back, so no road test data.
Now it is not that hard to figure out what I got to do, but what I am asking is does a new MAF sensor affect the tune by that much?

I do need to get some more data, but looks like I got to lean it out a bit.

Try switching the MAF relay with either the fuel pump relay or Burn-off relay to see if it makes a difference before changing the tune. I chased some drivability issues before and the relay turned out to be the problem.

That is an interesting idea, never thought of that. The relays usually give you a code 34. I did get that long time ago, and changed out one of them relays. I think the FP relay is a different p/n. I did get a code 34 when the MAF failed, and 33 when I pulled the connector. Easy thing to do.
Anyone else?

A new sensor may be calibrated slightly different from stock. It may read a different grams/sec value at one voltage level than the stock sensor would, so in that sense, fueling would be off.

If the relay is bad, check that first, but I'm willing to bet that you need to work on the MAF tables or scalars to dial in the fuel curve again.

Well I hope I dont have to get into them MAF tables/scalars. I messed with them once, dont really want to go there.
Tonight I tried changing the FI constant, see if I can get the BLMs up. First attempt was no help, idle BLM was 108. It would jump up to 128 when I reved motor up, but then go right back to 108. I made another change and got it to idle at 116. Now I know, I need to get a road test in to see what is really going on. Will do soon.

The other thing I don't like, is that when I pull the 20amp ECM fuse, it is quite warm to touch. I have seen this alot lately since all this MAF stuff going on. I mean, what is pulling all that current to make the fuse so warm? Is that normal? I will also swap the MAF power relays just for fun.