Hi I have a 1990 ford ranger XLT with a 4.0 and it has developed a very weird issue it starts fine cold but once it warms up the idle gets very erratic it will idle all over the place between 1000 and 1800 rpms and will run fine when up to speed but will stall out coming up to a stop sign and is almost impossible to restart after this happens if you hold your foot on the gas and brake at the same time when you come up to a stop it will keep it from stalling but once you stop if you can keep it idling it will idle fine until your step on the gas then it will stall out I’m very stumped at this point

 

It would be helpful to know is the check engine light on? if so what codes do you have.
Since your stumped what diagnostics steps have you taken ?