81 SC running / idle problem
 

I have tried searching but have not had much luck. Any help with the problem or search terms would be appreciated. (a bit of background) When I used to drive the car every day it would always start on the first crank. Recently it has been sitting for a couple weeks at a time between drives. When I go to start it it starts up right away and then idle falls to a couple hundred rpm and either dies or struggles for a little and recovers. After a second try it usually goes through the normal warm up routine and runs fine. After it is warm it starts the first time with no problem. I thought nothing of it until this weekend.

I took it out on a longer drive (about and hour each way) and it ran fine however on the way back when i was exiting the highway and slowed at the top of the offramp the car died instead of idling. I was able to restart the car while rolling enough to pull into a gas station. I tried to restart it and sometimes it would crank and not fire, however more often than not it would start and run briefly at about 2500 rpm and then fall to a couple hundred and die. I was able to get home by keeping the throttle up at stops. The engine was also very jerky on the way home, and backfired on deceleration. When I tried to restart when the engine was cold it would hover around 2500 for a couple seconds and then fall and die. I was able to keep it running if I kept the throttle up but the second I let off it would die.

From the search I have done I believe it is something with the CIS, Im not sure what it is but im hoping its nothing too serious. Any help would be greatly appreciated.

There is no real good substitute for following the CIS Troubleshooting Procedures. There are a variety of aftermarket books that can walk you through this. Unfortunately, one of the first steps is to verify the proper system and control fuel pressures which requires a fuel pressure testing tool. Frankly, it's available fairly inexpensively from Whitneys.

There is an Auxilliary Air Valve, which allows additional air in during warmup. This, combined with the fuel pressure action of the Warm Up Regulator, acts as a choke. Further, there is a Cold Start Valve that sprays fuel during starting, with the duration of the spray being dependent on temperature. These systems all have to work properly. Additionally, there can be no air leaks in your air box. It is pretty tough to track down CIS system issues without first verifying what DOES work properly. The Auxiliary Air thing can be verified independently, but you may very well need to know what your fuel pressures are.