my 87 rx runs almost good now until i get on the freeway. when the engines warm the check engine light comes on and if i go faster than 55 it jolts real bad and my boost gauge shows right on zero and the turbo spools and in 5th gear, when i floor it the boost goes to 9psi instantly and takes off quick and doesn't cut out if im accelerating even a little, the car gets real bad mpg like 15-20ish and about 175 per tank. the car rolls freely and nothing seems to be hanging up, i can even cruse in 1st gear and and rpm above 3k it jolts, pops, and spudders, unless i get on it and it gets full boost by 2k rpm i adjusted the tps to get best vacuum which is about 18psi at idle so what could this be? Im going ej real soon but i wanna know whats up with it

Have you checked the cracking hard vacuum lines that go to the boost controller on the passenger side of the engine bay? I'd start there. Also, pull the codes as it will also help to figure out the issue.

I should check the lines. But I have 14 21 22 23 24 I believe for codes but it's still strong and fast just doesn't like cruising the boost gauge needle jumps and flickers a Tad bit under boost

14 - Injectors 1 and 2

21 - Coolant Temperature Sensor or Circuit

22 - Knock Sensor or Circuit

23 - Air Flow Meter or Circuit

24 - Air Control

 

Start by checking all the electrical connectors to make sure they're plugged in properly. Then disconnect the battery and way about 10 minutes for the ECU to clear the memory, reconnect and see what codes come back.

 

CTS is usually because the connector on it is corroded and making a poor connection. I recently had to replace mine along with the connector as they were green from corrosion.

Sounds like a vacuum leak to me. The airflow meter tells the ecu that there is more flow than is actually being delivered to the engine causing excessively rich conditions and the symptoms you describe.