Driving car on D3 in the highway bad for engine?

I have a 2000 Honda Accord ex. Recently I have a vacumm issue while driving in d3 but not d4( not so far ) but I have driven the car on the highway in d3 several times because one of my friends who works on cars told me that it saves gas if I had done that and i was online and read that it's better for my car if I have start with d3 then shift it to d4. Stupid and I know not to believe everything I've read online. Anyway those trips are 30-40 miles and I driven it on d3 on the highway about 8 times. About an hour long trip each time. Did I do major damage to my car and is the vacuum problem because of my driving?

1999 Honda Accord ex 2.3L?

Okay guys i have a 1999 honda Accord EX 2.3L seadan. The car is a daily car also i do delivery 6 days a week running around 2,000 to 5,000 miles a week. The question I'm about to ask is what can i do to make my car performance better as of right now it's all stock.

As of now in the car

Spark plugs bosch spark plug iridium
Spark plugs wires from napa
Oil i use 10w 30 castrol full synthetic
Oil filter is fram

Few thing i bought for next oil change

bosch spark plug iridium
10W 30 castrol full synthetic
Bosch distance plus oil filter

That about it what I'm really looking for is performance parts for the car to help it run a litte better. Also miles on it 180, xxx almost 190, xxx

I was thinking of stuff like cold air intake and new exhaust cause on a busy delivery my car take a beating from it.

What would cause my 2001 honda accord to just die while driving?

I have changed the ignition switch and it still dies at random and I have to wait a few mins for it to chank up again. Sometimes when I hit the panic button on my remote and then unlock the car with the remote it will start up and run fine for a while then do it again.

I washed everything off under the hood of my 90 Honda Accord LX now it won't start?

I just purchased the car and it seems as though there was a oil leak at one point because everything was caked in grim and oil from the engine to the under carriage. I washed everything off under the hood with my house hose and baking soda a rag and tooth brush for hard to reach areas. I scrubbed the engine because it was black due to oil burning on it over a long period of time. It's now shiny and looks almost new but this morning I went to start the car and nothing. My neighbor came and gave me a jump it started right up but the second the jump cable was removed it just shut right back off tried again this time leaving cables on a bit longer but same thing it turned right back off with removal of cable. What could be wrong? Also my battery light is now on

I have a Honda Accord 92. With new battery and starter. Still won't turn on?

So when my car stopped turning on I hit the starter a couple of times like my dad told me and it started. After a while this stopped working. I changed the starter myself. And it still wouldn't start. Only made a buzzing sound. My dad told everyone it was the battery so he bought a new one and we put it in. It did the same thing. I'm 17 years old. My dad said I needed to fix it. Trying to teach me to be responsible with my things.

How to cope with this situation?

19… Got an average job no less than 2 months ago. Living with mom and brother still however she is on the verge of bankruptcy or she is already bankrupt not sure, all I know is that she can't afford the 3 cars that's she's paying for ( 2 Honda accords and a civic, late models 2013-14) and she's gonna lose two of them in two weeks. She might get to keep one I'm not sure don't have much info but does being bankrupt mean she's going to lose everything? I mean we live in a low incoming housing authority… Lived off food stamps which will be cut off soon maybe i don't know how it works
But I've lived in a way where I see money is everything, happiness or worthless at the same time but I try to be humble sometimes but I hate the fact that we're not "average" like we use to be. Personal problems I know that have been conflicts so far are my mothers previous gambling pit blend which she claims to have stopped going to the casino with her out of state boyfriend, And my youngest brother whom use to take up after me but became worse And had to be put in foster care now he's doing better but his life seems more content even though it's not the life that I would prefer to live because of social matters and whatnot but I have changed myself in ways I thought I couldn't have done so. As in quitting smoking and partyin and have been 3 months clean so far I've been working out for the past 3 years and have gains that can boost my confidence through a skyscraper, I'm in Tech college now

I'm want to buy a car soon but i can't really decide 16.Lexus is250, Genesis coupe?

Main - Lexus is250 (2007), Hyundai genesis coupe (2011), Mazda 3 (2010 or 2005), Nissan Maxima (2010), Nissan Altima (2007)
thought of: Honda Civic (2007), Honda Accord (2009), Chevy Cruze, Chevy Malibu (2010), Toyota Camry (2008).
i like sporty cars but i don't mind if its not just as long as its good looking. Nice interior as well.

Added (1). I want to buy a car soon but i can't really decide, 16. Lexus is250, Genesis coupe?