View Full Version : Idle speed control actuator (motor)

12-10-04, 02:51 AM
I have a 95 SLS and having trouble starting when cold. It starts right up if I depress throttle slightly. Just replaced FPR. It starts just a few more cranks than it used to. I also noticed that ratchiting sound after shut down, only twice, so it doesn't ratchet every time. It also idles and runs perfect. Has anybody experienced this with a 95 or older northstar?

12-10-04, 01:10 PM
If the idle speed control motor has started making the racheting sound it is likely failing/failed. Replacement is the cure. Search using the forum search feature and type "idle speed control motor" into the drop down box and read my posts for more info then posts questions. Much has been posted and covered in the past on this.

12-13-04, 09:55 PM
I have a question for Bbobynski, I changed out the ISC motor, cleaned throttle body and also performed T.P. idle learn procedure. My question is should the it fire up within 2 seconds like perhaps a vortec engine or is it normal to crank for 5-6 seconds. Not really sure because I may have had a slightly leaky fuel pressure regulator for a while and car would always fire up within 2 seconds. Of course I just replaced FPR, Or maybe I should adjust hex bolt on end of ISC motor further to see if this helps? The car idles and runs absolutely perfect no hesitations or stumbles.

12-14-04, 08:17 PM
It should fire almost instantly. Crank times are virtually zero on the Northstars if things are right.

Adjusting the plunger will not affect this. The plunger position is controlled by the PCM so screwing it out further will just screw up the PCM control...It will still seek the same throttle angle for crank regardless of what you do with the plunger. Unless you are hearing some racheting noise on cold start the plunger is fine. IF it is racheting that means that the plunger is not long enough to have full authority for the cold start crank throttle angle so it needs to be lengthened. But if you are not hearing any racheting (the tapping of the accelerator pedal on cold starts) then it is fine.

Something else would be causing the longer cranks. Spark delivery is almost instantaneoud so the most likely culprit is fuel. Sounds like the fuel pump may be getting weak and thus it is taking longer for the fuel pressure to build on cranks. A quick check of fuel pressure with a gauge screwed onto the conveniently provided schraeder valve fitting at the throttle body would tell you. The pressure should jump up instantly during crank and stay solid.

A failing fuel pump will often show first signs of long cranks as the pump output is deteriorating and thus is more affected by low voltage during crank. The high draw of the starter causes the pump to slow down due to voltage drop during the crank and then the fuel pressure drops and the crank takes even longer. Interestingly (never though of this before) a leaking fuel pressure regulator could probably mask this. The FPR leak would add fuel during the shutdown so as to help the next start which would normally be too rich with the extra fuel if the pump were working correctly. Hmm....could happen...quite easily.

Check the fuel pressure before doing anything rash.

12-14-04, 09:15 PM
The last couple of cold starts I have been turning the ignition to on for a short duration before starting car. Seems to start quick that way. Looks like I will need to purchase a pressure gage and hope it's not the fuel pump. This would be my 3rd G.M. car from the 90's I had to replace fuel pump.

12-15-04, 11:56 PM
If turning the key on several times before starting helps that tends to point ot the fuel pump as that will "prime" the system and build pressure while the voltage is still high before the starter draw sucks it down.

Find an older refrigerant refill kit for an R134a car.....they are cheap these days. The fitting is exactly the same as the fitting on the fuel rail (no accident...he he he). Cut the hose, score a cast off gauge in a cheap tool disposal store and you can have a servicable fuel pressure gauge for cheap.

I'm betting it is the pump.