1988 fc gxl N/A stick. Idle/ other problems.
 

Rough idle below 900 rpm it shakes the engine and car and sometimes kills itself or struggles to being back up to 900 +/-. Mounts seem good.
1st 2nd and 3rd gear works but suffer loads of power loss and 4th and 5th have no power. Got to 100 in 3rd then when in 4th i started loaong speed.
Has magnaflow aftermarket exhaust and all new spark plugs.
I am told vaccum leak for the power loss is likely,
and to swap or clean the fuel filters. What else should i look at. Pictures are helpful as im new to the rotary scene.
One more thing is when in neutral and shifting into first the engine struggles hard to not die from the drag of the transmission and throttles the rpm up and down trying to gulp the fuel.

Video
 

Clean the engine grounds and adjust the TPS to 1K ohms with a multimeter. I had a lot of weird symptoms with my car until I did these fixes.

Does your car have functioning aux ports?

Does your Exhaust have a presilencer?> I've read on here that you may lose some upper end power when your 5th and 6th ports don't open or are stuck "AUx Ports-5th/6th"

I just watched the video and god damn, that thing is rumbling!

Check out this guide here to service your ground points.

Stand on the passenger side of the engine bay and look down toward the exhaust. This is where your aux ports will be. Here's a picture. 'B' should be a metal pipe that runs down to the middle of the exhaust. 'A' goes to those piston looking things to the right, make sure you have those still and that they don't look ghetto rigged.

Those work for your six-port fuel injection, and they activate at higher RPMs to add fuel. They are activated by the pressure from your exhaust. If they aren't functional, you lose a lot of horsepower. Some fools zip-tie them to keep them open but this makes your car run super rich at low RPM.

Tomorrow i will be checking what you mentioned and posting what i find for yall to see. Clarification when in 4th and 5th if i floor the throttle i lose speed. 4th is a slow fall, 5th is like there is no throttle.
Great ideas so far so ill let ya know asap

5th is already overdriven, like others..check TPS... i would also visually inspect to see if your AFM cone ont eh inlet side is moving freely. ...check vac leaks.

good luck