350 bad low idle
Have you checked for vacuum leaks? Use carburetor cleaner and spray along the intake where it bolts to the heads. Also spray along front and rear gasket and the throttle body base. If the idles speeds up that is where the vacuum leak is. Is your check engine light on? You need to get a full scan on the OBD1 system. get a REAL reading on the OBD1 system so you can see what all the sensor values are at when the truck is at full operating temp and at startup. Scanner will tell you what your IAC counts are, pulses of the injectors, voltage at the TPS through the whole throttle range, millivolts on the O2 sensor, timing adv/ret, knock counts ( retards the timing when they happen) even the hydraulic pressures in you tranny.