Hi, so i have an issue i have been chasing for about 2 weeks now i dont know what do to anymore
car is a 86 fc Na 6port Stock engine only goopy apex seals

Car starts up and runs fine at about 1400rpm
then after 20ish seconds the rpm drop to about 1000 and starts jumping to 1300 and starts sounding like a horse flapping its lips when i tap the gas lightly it is missfiring until about 2000rom then runs smooth and good also has full power
but on deceleration it still sounds like a horse

I changed the lower intake gasket for a new oem one because i had a selfmade one in and then this started car was running perfect for 4500k km after the rebuilt

What i did so far:
-I smoked the whole engine intake system and vacuum lines nothing is leaking i also sprayed every crack on the intake system with a starting spray nothing changed
-I replaced all vacuum lines and checked all valves on the rats nest
-i checked bac tps and thermwax all working and in spec
-i replaced spark plugs and wires
Car has good spark on all 4
-i put in spare coils
-i adjusted the timing with a light
-i checked all wires on the engine no shorts
-i put new o rings on bottom and top on both primary and secondary injectors and checked if they are working
-i put new gas in it and premixed it bc omp
is gone
-put in a spare ecu
-checked fuel lines
-checked fuel pump
-compression is abput 130~on all sides

I dont know what else to do so im here

https://youtube.com/shorts/ms3EtU4FOwU?is=ylhen2xf3RHa808e
here is a youtube link for the video

 

Have you tried pulling codes?

 

I will do it tomorrow when i get home

 

The horse sounds are more of a Mustang problem...

Just kidding. It sounds like there is a vac leak, which I know you said you checked, or something vacuum/throttle body related isn't hooked up right. I would wager there may be a vac issue first, somewhere that might not be part of the system when the car is off and you are doing a smoke test.

 

ok so i had a busy week with end exams


No codes at all

 

I smoked the car again today and i found 2 leaks one on the temp sensor in the upper intake manifold under the bac and one on the block of plate on the egr fixed both
i also replaced the fuel lines since they looked bad and the feed from the filter had a crack
buttttt
still running shiaaat

 

I watched the video again, and reread what you posted. If you believe you have all the vac leaks taken care of, here's the next things to check.
Throttle Position Sensor
Primary Throttle Plate Position
Timing

The engine does the accelerated warm up cycle and then returns to idle. The accelerated warmup is intended to get the sensors up to operating temperature for correct fuel injection. This cycle is performed mechanically with the thermowax piston attached to the throttle body. It holds the primary throttle plate slightly open to raise rpms. Once the throttle body is warmed up, the thermowax piston retracts, allowing the primary throttle plate to close to idle position. The throttle position sensor tells the ECU when the primary throttle plate has returned to the idle range. If your throttle body has been adjusted, and by adjusted I mean monkeyed with, then you have to start from scratch. The only idle adjustment should be at the BAC. That is an airbleed screw. The screw at the primary throttle plate is intended to be a bump stop to stop the primary plate from slamming shut against the bore. If someone has used that screw to raise your idle, then the ECU cannot find its point of reference for idle conditions. This can cause the hunting rpms that you are seeing. It's either improper fuel, or improper air, and if your throttle body has been altered from the factory position, that can cause you a bunch of headaches because the ECU can't tell you what's wrong.

Check your throttle position sensor first, according to the FSM procedure. If it doesn't read correctly, you may need to inspect your throttle body to make sure the primary plate is in the closed position. If both of those are good, then work with both your timings, and idle air adjustment screw to dial it in.