View Full Version : 4100 HT Idle speed setting

10-20-12, 01:45 PM
I have a 83 Eldorado 4100 HT. With your help ( guys from this forum) I've manage to tune my car almost perfect. So thank for help so far.

Now I have another problem. I'm trying to set the idle speed on my car. I have few problems with that. Now my ISC motor is fully extended and the setting screw is fully retracted. When engine is hot car idles at around 1000 rpm.. too much I know.
I have tried to set the idle speed according to manual but I didn't mange it.
I have warmed up the car, turned off all electrical users and AC, and checked the timing ( is set to 12 degrees, I,m running on 95 octane fuel (EUROPE)). Only thing I didn't do according to manual is ground the green test connector near alternator (I didn't find it). Then I have unplugged connector from ISC and retracted the motor completely connecting pins C and D to the battery. Then I've managed to set the Idle speed (with unscrewing screw at ISC) to approx 550 rpm (according to manual). I've turned off the engine (ignition to off) for 10 second. When I started the car it idles normal at 550 rpm, but when i reconnect the ISC motor to the connector it extends again completely.

What am I doing wrong, why computer always extends motor completely, how can I convince car to idle at correct rpm....?????
Please help.


Best regards,


10-22-12, 09:02 PM
With the engine to normal temperature and climate controls off, open the throttle arm on the throttle body slightly with one hand and with the other press forcefully on the ISC shaft and hold that pressure till it fully retracts, then quickly disconnect the ISC wiring connector. Let the engine come back to idle. Now verify its idling at about 450 to 500 RPM WITHOUT the ISC shaft touching the throttle arm at all. The base idle is adjusted with the throttle stop screw on the base of the throttle body. Now adjust the gap from the ISC shaft to the throttle arm to approx. .060 inch. (60 thousands of an inch) Shut car off, reconnect the ISC connector. Count to 10 and restart the engine. Engage the climate controls in any mode after ECON. Assuming the A/C compressor engages, watch the ISC shaft. It should extend slightly just a milli second before the compressor engages. If it does not move, it needs replaced. And if replaced, it must be adjusted as mentioned above.

10-22-12, 09:51 PM
Take it easy pressing on the plunger - "forcefully" can be misleading. All you need to do is close the throttle switch. It takes little/no effort.

Remember, just about the entire ISC is plastic, inside and out...

10-23-12, 01:07 AM
I guess a better word would be firmly. The main thing is to continue to press until it fully retracts and quickly remove the wiring connector. The manual says if the connector is left connected and the shaft is retracted, damage to the "driver" within the ECM can happen.

10-24-12, 04:40 PM
Thanks guys for the advice. I've done everything correct and now I've found out that my TPS is playing funny. In closed throttle circuit it has value 13 on ECM and according to manuals it should have 0. Now I must first try to set or replace TPS and then I thing everything will be OK, because whenever system was in closed throttle circuit the ISC wouldn't retract, but when I've touched throttle just a little bit it retracted for a small fragment and so on.... So if I was pressing throttle continuously ISC retracted. Tomorrow I'll try to set TPS and see how it goes...

Thanks for the advices.

10-25-12, 12:13 AM
That's what I said, open the throttle then press until the ISC fully retracted. The 0 setting is done with the ISC fully retracted and a gap of .060 and the base idle speed must be at or below 500 RPM.