When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The Idle Load Compensator - How Is It Supposed To Work?
I have an '85 Delta 88 with 49K verified original miles and a Rocket 307. An issue I have had with the car since day one is idle speed when the A/C is on.
Right after I bought the car in 2022 I started the A/C and found that oil pressure at a hot idle in drive was around 5 PSI which would cause the driver reminder feature to go off if I sat at a light too long. I used a tach to check the hot idle speed in drive (without A/C) and it was around 550 RPM which was correct according to the fan shroud sticker. I didn't think this was high enough, so I was able to grind a skinny screwdriver to fit into the ILC's rear port and adjust the screw for 650 RPM in drive (without A/C). In this state, oil pressure is an acceptable 20-25 PSI but despite the increase in RPM, oil pressure still drops to 5 PSI when the A/C is on in drive.
To address a few possible issues:
1) Yes, I have verified the mileage on the car and I am certain the engine is not worn out. It was bought new in '85 by an older guy who kept service records in the glove box and they show frequent oil changes until he passed away sometime in late 2021 / early 2022. After that, the car was bought by another older guy who just saw it as an opportunity and kept it for a few months before I bought it.
3) The oil pressure gauge sending unit failed shortly after I bought the car, so I have replaced it, but the readings did not change from what I saw on day one of driving the car.
4) I use 10W-30 oil and continue to change it regularly - I am considering going up to 15W-40 because of this problem though.
5) All vacuum lines are hooked up correctly and do not have any rips or tears in them.
I have done as much reading as I can on the ILC, but have found conflicting information. The 1985 GM service manual I have for the car doesn't mention anything about idle speed when the A/C is on, only saying the ILC is controlled by the ECM to prevent the throttle from snapping shut when it is let go at high RPM. On the contrary, I have read others state the ILC is also for bumping up the idle speed when the A/C is turned on, but mine does not do that. However, my GM manual does mention that on cars with the VIN code "9" 307 there is an "Idle Speed Solenoid" in place of the ILC that is solely for increasing idle speed when the A/C is turned on.
In this case, I could probably solve this problem by just moving up to 15W-40 engine oil, but I would like everything on the car to be working as it should first. Unfortunately, the lack of information on the ILC prevents me from knowing weather or not it is working properly and if any work needs to be done.
Any information you might have on how this thing is supposed to work would be greatly appreciated!
I didn't, but it drops far enough to reduce the oil pressure from the mid 20's to roughly 5. I have not used a tach to verify, but my guess is that it's somewhere between 400-500 RPM.
What I'm mainly looking for is information on weather or not the ILC is supposed to bump up the idle speed when the A/C is on since all of the information I have found thus far is conflicting.
At 400 rpm your engine is on the verge of stalling, so yes the oil pressure is going to drop. I am not familiar with this particular system but I would think the solenoid or control motor or whatever they call it would bump up the idle with the a/c on. As has been said a million times on this forum you need to get a copy of the chassis service manual for this vehicle. The manual should explain how the system works and how to diagnose and adjust it.
The ILC appears to be a variable power dashpot, controlled by the computer, to do as described. The idle speed solenoid, on the other hand, doesn't do any of that variable vacuum stuff, it is just ON or OFF. It can also be used as an anti-dieseling device to shut the throttle down more when you kill the engine.
If you can't make the ILC love you, recommend you fit an idle speed solenoid per factory methods and tie it into compressor on power. Set in gear idle no AC with the carburetor screw. Turn AC on, the solenoid will extend, you may have to blip throttle, then, set it to give you same RPM with AC on as you now have with AC off. It will crack the throttle a little more open with the solenoid.
Give no cares about the emissions stuff on the ILS, the throttle can slap shut all it wants provided you don't die.
I had a dieseling problem and fit an idle stop solenoid to be on when ignition on. When shutting it down, the ignition stops, but the throttle also drops to about unsustainable idle, like 500. It gets rid of 90% of the dieseling.
Once again, read the manual. There are 1 1/2 pages in the 1985 CSM about properly adjusting the ILC and associated vacuum control system. The ILC extends when there is no vacuum applied and retracts to lower idle speed when there is vacuum applied. One thing this does is help prevent dieseling when you turn the engine off, as there is a vacuum storage ball and a vacuum delay valve that retains vacuum in the ILC so it retracts for a short period of time after the engine stops running. This lowers idle speed so the then engine doesn't sputter and run on with the key off.
You don't want to hear this, but assuming the gauge is correct, your low oil pressure is likely due to a worn engine.
There's no setting curb idle speed with the ILC. It's done via ECM and feedback.
I'm afraid that is not correct. These OBD I systems do not have the capability to control idle speed - there is no idle control motor or anything like that. The ILC is binary - it is either extended or retracted. There is no feedback and no proportional control. In fact, the procedure on pg 6E1-122 in the 1985 CSM specifically tells you to not adjust the ILC unless curb idle speed is not correct. If that is the case, the adjustment through the access under the rubber cap is exactly how it is done. On the other hand, that adjustment procedure has specific conditions, not just doing it by ear.
As has been said a million times on this forum you need to get a copy of the chassis service manual for this vehicle.
I have this manual, actually (mentioned in my original post). It is the same one Joe has pictured above.
Originally Posted by Olds64
You also never mentioned what gauge you are using to measure oil pressure
It is the factory oil pressure gauge in the car's dash. As I mentioned previously, I have replaced the sending unit for the gauge, however I am certain the engine is not worn out so I am starting to question the accuracy of the gauge.
Originally Posted by Koda
If you can't make the ILC love you, recommend you fit an idle speed solenoid per factory methods and tie it into compressor on power. Set in gear idle no AC with the carburetor screw. Turn AC on, the solenoid will extend, you may have to blip throttle, then, set it to give you same RPM with AC on as you now have with AC off. It will crack the throttle a little more open with the solenoid.
Yes, this is exactly what I am looking for.
I thought the ILC was supposed to bump up the idle when the A/C is turned on, but I was not sure, which is why I created this thread asking if anyone knew weather or not that is true.
Though I don't have a clear answer, it sounds like the ECM does not adjust the ILC when the A/C is turned on so I may end up installing an idle speed solenoid to give the bump in idle speed I am looking for.
Originally Posted by joe_padavano
If that is the case, the adjustment through the access under the rubber cap is exactly how it is done.
That is precisely how I adjusted mine, using the modified screwdriver I mentioned earlier. I used a tach hooked directly to the HEI distributor, and adjusted the curb idle from 550 to 650 RPM using the screw behind the cap. I did not touch the plunger.
March 22nd, 2024, 10:27 AM
