Stolen 1993 Civic hatch with aeromods... Update: FOUND!

[Cd]

( Car : 1993 Civic Dx hatchback automatic, with 130+ K Stock EPA 42 Highway MPG )


My car is now getting under 30 MPG.
It pulls to the right enough to make me drive off the road if i let go of the steering wheel for about 3 seconds at 75 MPH.

So what is that, at least a -5 MPG loss ?

My brother in law repaired the wiring on the car and "surprised me" by finding a parts car and installing a few things.
I was " surprised" to see that the car now has an aftermarket ducktail spoiler and passenger side mirror.
It also lacks the factory undertray and front spoiler.
All body sealing around the lights and hood was pulled out.
So, great intentions, but now my car has the worst drag it has ever seen.

I figure that amounts to about -2 to - 2.5 MPG over stock at 75 due to increased drag.

So, a total of -7 MPG at 75 MPH with the A/C cranked up to one click under maximum. ( I have a dog now. She likes to stay cool. )

I figure the car should get 35 - 37 MPG in these conditions with a healthy engine / transmission.

What's your guess ?
I obviously need to get the tires aligned, but do you think that bad of MPG points to something else wrong with the car ?

BTW, It may be even worse than 30 MPG, because I was able to drive behind an RV ( I could see his mirrors ) for half of a 130 mile trip that gave me 30.7 MPG.
( Going around 65 -70 A/C on )

The car starts right up, and has no misfiring. It does lack power, but it never really had any since day one.

- Thanks guys !

[Cd]

Update since my last post : I had my car's wheels aligned.
I can let go of the wheel at 70 MPH, and it now takes a several seconds before I reach the side of the road. ( versus right away as before )

However, there is no change in my MPG.
The car still got 31 MPG on the 130 mile trip to my parents.

I plan to take the car in for a check up, and would like to know what to test for.
All the obvious things seem fine. Plugs and wires are good. Idle is good. Oil is fine, tires and tire pressure are fine, transmission is fine, etc.

[MeteorGray]

It may be a fueling problem. Check the air-fuel ratio; perhaps too rich?

[Piotrsko]

Finger In the tailpipe. If it's black you might be rich but within O2 sensor parameters. Plugged Cat. Never replaced air filter. Leakey injectors. Go on from there.

My vehicles, on a straight road won't wander off to a side for a good long while. When the front tires are low, my golf tracks the grooves left by truckers tire chains for miles, even around curves.