ISC ? How do I Test it

[heliman]

1990 Chevrolet PU with a 4.3 V6 engine. It has TBI. I removed the computer and tested all four wires to the ISC. They were good also. then I checked the ISC solenoid and it tested good.
But still the engine surges and the ISC doesn't move. Any questions would be helpful
Mike out in Arizona

 

[tcsalvage]

ISC? do you mean IAC (idle air control)? if you tested the iac wiring and thats good did you clean the carbon buildup without moving the plunger on the iac and remove the throttle body and clean the carbon buildup to the base through to the intake. if you ran the iac out of the throttle body so it couldn't seat it might very well be junk since the ecm reseats it every time you turn the switch on.

 

[Mmfh]

Have you check for any vacuum leaks? Have you messed with anything else when this started happening?