When I start my 1990 plymouth laser it will idle normal for about 3-5 minutes. Then the idel speed go's up and down constantly if you try to drive it with will be running about 500 rpms even if you foot is all the way on the gas. And it will nearly stall. If you turn the car off and back on you can drive it fine for about 1-2 minutes before the same the happens where it nearly stall and runs very low rpms. With no check engine light on i can't get any codes. I'm not sure what to try at this point. I've got a new ECU in it and that fixes my no start problem. Any help is appreciated thanks.