Hey so pretty new here, but couldn't find an exact post that I was looking for.

My car has about 120,000 miles. It's automatic with 4 cylinder. Not a car pro, but have learned a lot.

I've owned it for about 14 months now, and within the last 3 months the problems have suddenly came out on me.

I was driving at about 25-30 mph when the car jerked and the RPM's went up about 600-900 and my AT light was flashing and my engine light came on.
I took it to a shop and they said it was a cylinder #1 misfire and my speed sensor should be replaced. We cleared the codes and this happened about 3-5 more times.
From then I had noticed a loss of power and higher idle of RPM's. There were a few times the RPM's would drop to what used to be normal, but then immediately go back up. I could tell I was on 3 cylinders.

Cleared the codes and just about a week ago had my speed sensor replaced. I thought this would possibly clear up the problems. As soon as I drove away from the shop I could tell I was still on 3 cylinders.

We have replaced the spark plugs and the connectors to them.
I don't know what else I can do at home myself to figure out this problem. My dad(I'm 20 in college) knows that it is on 3 cylinders and I've told him. It hasn't had problems since it's been on 3, but I don't want it to be causing more damage. And I really just want all my cylinders working.

Stressed out about all of this. Don't have money coming out of my *** to fix this immediately.

 

Good thinking. Get it fixed to save on replacing a catalytic converter.

Here is a list of things that can cause a misfire (Thanks for this list, UseYourNoggin!):
Missfires Can Be Caused By a Million and One Things,

Vac Leaks
Wiring Issues
Spark Plugs(Even Fresh Spark Plugs That Are Crappy Quality.... E3 And Such)
Ignition Coils
Alternators (Search EMI)
MAFS
Injectors
Injector O-Rings
Intake Gaskets
TB Gaskets
PCV Hoses
PCV’s
Malfunctioning EGR
Malfunctioning CAS
O2 Sensors
Aftermarket Intakes
Intake Hoses
Vac Lines
Timing Chains
Timing Chain Tensioner
Broken Cam Gears
Malfunctioning Cam Sensors
Incorrect Crank Gears(The I4 Has Like 40 Different Configurations For Whatever Reason)
Incorrect PCM Flash
Issues Within The PCM
PCM Wiring
Bad Diaphram Within The FPR
Issues Within The fuel pump
Dirty Fuel Filter
Dirty Fuel Lines
Pre-Cats/Poor Exhaust Flow

What is the code you are getting? That could help narrow down what you should do first.

Focus on those causes that would only affect one cylinder. Look if there is oil at the bottom of the spark plug tube. In this case clean it out and replace the valve cover gasket.
Check the fuel injector.
Check for vacuum leaks at the lower intake manifold gasket in particular at the cylinder that misfires.

 

need that code.sparck plug cables or coil packs comes to mind. if you know what cylinder is misfiring, try swapping the position of the coil packs. if the misfiring cylinder changes position, change that coil pack. coil packs are not that expensive and replacement is easy. you can also test the coil pack by removing the spark plug cable and holding close to the valve cover and checking for spark. the other section of the coil pack can be checked by removing the pack and connecting a spark plug to it. let the spark plug touch the valve cover and tell an assistant to start the car. you should see a spark. if not, replace the pack. each pack fires 2 spark plugs.