1.5L Tech Page
Here you can find various FAQ's I think of on the Mirage.

Hard Starting when cold, raining, damp, or cool out or hot weather
 Computer theory:
The computers on these cars, (4G15 89-92) were known to be "bad" at one point or another.  I personally went through two computers already since mid-1998. My current one is out of an 89 Excel.
The first time the computer went, I tried starting my car after school (it was hot outside) and the car would crank and crank and crank, but no start.  A lot of starter fluid and (luck?) got the car started once.  Once it was started it ran just fine. It was never to start again.  Had it towed to Satan and diagnosed as a dead ECU, code 1.  Bought a new one for $150 at an online junkyard.

The second time the computer went was at my dads workplace.  It was warmer out, and I went out to start my car and it would crank, (sort of a high pitched quick revving sounding engine, but no go)  I had symptoms on this one. For the past few weeks the car would take forever (up to 10 minutes to start) when it was damp, cool, or raining out and it was the first time starting the car in the morning.  I didn't think much of it, and tried some starter fluid.  Most of the time it would kick the car to life, and the ECU would take over from there.

When the computer went this time, I decided to to some diagnostics.  At the coil, I was getting some very weird readings.  The voltmeter would jump up and down when the engine was cranked. Very sporadic power surges.  I think I remember someone and TMO checking out our ECU's to see if they could find the problem for years, but no go. 

My theory is that the ECU's are junk :)  Anyways, if you have any of these symptoms don't waste $100's of dollars on stuff you think it might be, find a computer for $100-$150.  Even if it isn't the computer that is going bad, you'll have a spare for when yours goes out!

Computers that work in the 4G15, 89-92 Mirage/Colt/Summits.
89-92 4G15 Mitsubishi Mirages (H/B or Sedan, only 1.5L)
89-92 4G15 Eagle Summits (H/B or Sedans)
89-92 4G15 Dodge Colts (Hatchbacks)
88?-91? 4G15 Hyundai Excels (Engine looks the same, comp is under drivers side)
These computers are stamped HMC, for Hyundai Motor Co., maybe these are more reliable? :)
Not sure if any other Hyundais work, but check em out.

How to really check if your computer is dead.
Hopefully you have an analog voltmeter.

Right under your left foot, by the fuse box, you'll find a little black connector. This is the diagnostics port.  This is the port that Mitsu plugs its little computer into to tell you what's wrong with your car (and charges you $75 for something you could do for free)

Turn on your meter to volts, (DC). Out the + lead to the lowest left connector, and the - lead to the upper right connector. (It may be the other way around) 

Turn the key to the ACC position and watch the blips on the meter.
Watch for quick blips, and long blips. In any tech manual, you can find the meaning of these codes
First blips is the first number, second set of blips is the second number. 2 quick blips, 3 long blips is code 23.  I can look up these codes for you if you don't have a manual (shame on you)

That's it! By the way, when you want to lose that 1.5L for a 2.0 Turbo, find the FAQ on this page :)

Computer codes for the 1.5L Mirage and 2.0L Turbo Eclipse

1 ECU Dead
9 Normal
11 Oxygen sensor
12 Air Flow sensor
13 Intake Air temperature sensor
14 Throttle Position Sensor
15 Idle Speed control
21 Coolant Temp Sensor
22 Crank angle Sensor
23 TDC Sensor
24 Vehicle Speed Sensor
25 Barometric pressure sensor (MAS)
31 Knock Sensor
32 MAP sensor faulty
36 Ignition Timing adjustment failure
39 Front oxygen sensor
41 Fuel injector failure
42 Fuel pump or circuit
43 EGR
44 Ignition Coil
55 Idle Air control
59 Rear oxygen sensor
61 ECM and transmission interlock
62 Induction control valve
69 Right rear oxygen sensor
71 Traction control
72 Traction control