Random performance drop

[Wagamos]

Im still new to dsm's in general. I just bought a 1990 laser rs turbo. It only has 103k on it. Just did some basic maintenance to it and im still having a few problems. Just looking for some ideas on where to start diagnosing it. One problem i need some help with is engine related. Im getting the following symptoms:

-Hard to start(it is cold out so i do attribute some of it to that)
-Randomly it will bog down when im idling to around 500 rpms but will not die.
-Random power drop(very noticeable and is throughout all rpms)
-This is sometimes accompanied with a squeaky belt.
-Random decrease in power until I hit about 5-7 psi then it takes off like a rocket. The power increase usually stages up at both ~2.5 and ~3k rpms.
-Poor fuel mileage(could just be my heavy foot though...)
-Impossible to stall in first at least(let my g/f learn to drive stick on it and i was showing her what a stall was going to feel like and it just dropped to low rpms and but would not stall.) Im assuming this is related to the power problems but could be something different.

What I have done
-Spark plugs gapped to oem specs
-new air filter
-new thermostat
-new oil cap + valve cover gasket

What im thinking
-vac leak somewhere
-something wrong with throttle
-compression problem
-Ignition problem.

I bought the shop manual and am competent with working on cars. Just having trouble diagnosing this for sure b/c the problems are sporadic and not consistent. Sometimes the car runs perfect and has plenty of power but then othertimes these problems start up. I havent taken a ton of time looking around b/c I wanted heat before I fixed a sporadic problem with power.

Sorry for the book, hoping to provide enough info to get some direction on this one. Thanks for the assistance.

 

[Absit]

I'd do new wires and a can of seafoam, it's an old car. What octane are you running? A compression test wouldn't be a terrible idea either. This only addresses a few of your problems, but when you have more than one, you have to do one at a time.

 

[gusu]

If your alternator is REALLY bad it can do all of that. The reason being it gets better would be the belt is spinning fast enough to give a moderate charge to the battery.

But the other thing it could be is a horribly clogged fuel filter. As a fuel filter gets more clogged the harder it is to get the car to start.

I honestly would check and replace the fuel filter first. But I would still go ahead and check the alternator to be safe anyway.

 

[Tyeler18]

Boost leak test. Should be the first thing done when anyone has a power problem.

Next would be compression test.

 

[LiquidX]

+1

Always do a boost leak test. If the fuel filter wasn't changed, chane it. Get the alternator tested and check belt tension.

 

[Wagamos]

I run 93 always. Ill start doing those things you guys mentioned and post results when I get them done. I appreciate the starting points.