SC idle issue

bpotenzo · 06-11-2010, 08:08 PM

At cold start my SC jumps to 1250, then drops to 900 - no problem. After warm up idle rises to 2200. Pop the deck lid and idle drops back to 900. Close the deck lid, blip the throttle - idle back to 2200. I'm thinking I have an electrical issue. This problem started after I changed the bulbs in the dash gauges. Any input?

ossiblue · 06-12-2010, 08:17 AM

Strange. Can't see any connection between the bulbs and the problem, but I'm no expert either. Sounds like an air leak of some sort by the symptoms. Maybe the deck lid is pushing slightly on a vacuum hose and opening a pin hole leak. My first thought was the hose connected to the decel valve.

You might try this: open the lid (rpm drops) and blip the throttle with your hand. Does it hang up now or drop to 900? With the lid up, try manipulating any vacuum hoses you see exposed and see if you can duplicate your problem. Let us know what you find.

longhornchris04 · longhornchris04's Garage

Second with L.J. said. CIS doesn't have much that is connected to the electrical, not like a more modern EFI system.

What year is your car? If it has Lambda, that might be the cause... something short circuiting the O2 sensor equipment and changing your fuel mixture. I doubt this is the problem, but it could be.

psalt · 06-12-2010, 09:41 AM

Remove and check fuse 18. Just a coincidence that the same fuse for the bulbs you replaced is also for the ECU relay ?

If the relay and ECU powers up and the FV is pulsing, check the cruise control cable plastic connector, the bell crank linkage bushings and reset the throttle stop adjustment screw per the manual.

Scott R · Scott R's Garage

More likely the cruise control cable is routed incorrectly and when you shut the decklid it's pulling on it and increasing the idle.

bpotenzo · 06-13-2010, 07:47 PM

Thanks for the responses. I checked fuses, cruise cable, no problems there and no vacuum leaks. Convinced that the deck lid latch was the culprit, I removed the latch and put electrical tape on the back side of the latch and the back of the bolt washers. This eliminated metal to metal contact. I drove for 10 miles, no high idle. Problem solved? I hope so. For the record the car is a 1979 SC Targa, no AC, no mods other than cat bypass and chassis braces.