Bucking, Hesitation after Warm Up

[shields]

My 1987 325e runs great when cold. But as the gauge begins to reach the first quarter, the bucking and hesitation begins. It happens on acceleration and around 2000 RPM.

I've replaced the O2 sensor and the temperature sending unit. I've also done a full tune up, replacing the plugs, wires, distributer cap/rotor, thermostat etc.

What could be causint this?

Could it be a fouled Cat convertor?

Thanks in advance.

[Brew]

Check the wiring to the 02 sensor.

[KenC]

Fuel pressure regulator

[kowalski]

icv valve (Idle controll valve) clean it with carb cleaner.

[KenC]

icv valve (Idle controll valve) clean it with carb cleaner.

... if you want to ruin it. Use some electrical component cleaner.

[kowalski]

how would that ruin it? thats what everyone else has used, i used WD40 bu it didn'tr work verry well and im far to lazy to take it back off and redo it