I guess #4 cyclinder misfiring?

For check i removed all plug wires one by one. When it came to no.4 idle didnt change.

After this, i replaced rotor arm, plugs, wires, cap but still does same thing.

i can see spark from cable to cap but with no idle changes @4

what can be the problem?

2.0 Ford pinto engine with weber 32/36

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