: A/c and Low idle problems

06-24-11, 07:43 PM
ok so for the last few days its been mid 90s and i decided heh time for some good ole A/C. great idea until i start moving my car. the ac works fine with no crazy noise and it gets dam cold but after a few mins of driving (10-15) my car starts flickering the stop engine oil pressure light when i stop at a light. it doesnt sputter or shake but the light comes on, and goes away when i push the gas. i noticed that the idle of the car drops pretty good when in drive and the ac running, and once i put it in park or neutral the light goes away and the idle goes back up. i would like to know what is the possible solution to this without turning off the ac :)

06-24-11, 07:50 PM
Maybe the IAC (Idle Air Control) motor is on its way out?

I know there is a pressure switch on the power steering line to turn off the compressor during parking maneuvers.

06-24-11, 08:24 PM
The engine is underpowered without the A/C and with it on, the engine will be noticeably sluggish. The ILC (IAC) has nothing to do with this, and there are no steering sensors or pressure switches that turn off the compressor when parking.

The main issue is the oil pressure lamp, which indicates (obviously) that your engine is losing oil pressure at low idle. Have you checked the oil level to see if you have oil? If you have oil, then change oil pressure sensor, and see if the lamp goes out. If the problem persists, then that indicates the bearing clearances on the crank shaft are too wide. A temporary solution would be to replace the oil with a thicker oil, which will take up the slack and increase the pressure. The only way to repair the bearing clearances is to rebuild the engine.

06-24-11, 09:52 PM
I'm eager to learn all I can about these engines.
What does ILC stand for?

As to the pressure switch, I might have understood wrong, yet the FSM for my '95 Fleetwood states there is such a switch.

The text::: (( page 1B-5 ))

Idle Speed Control Power Steering Pressure Switch
Engine idle quality is maintained by temporarily shutting off the compressor when high power steering loads are imposed. The switch in the power steering pressure hose closes at approximately 3,447 kPa (500 psi). The hydrualic pressure is an indicator of the load placed on the power steering pump. When the pressure is reduced, the switch opens.

06-24-11, 10:18 PM
ILC means Idle Load Compensator, which does basically the same thing as the IAC.

Caddylover's car is and '89, which has a carburetted engine that does not have any sophisticated engine sensors, or anything above basic necessities. The last-gen Fleetwood (what you have) was 10 times more advanced and most of they equipment doesn't apply to the 80's cars. If they had it in '70's, Cadillac was still using it in '89...

06-25-11, 12:23 AM
yeah im thinking the pressure sensor is off. cause this car only has 81k miles on it and it rides just fine without the a/c. i never see that light during normal conditions. it has oil and new filter not even a month ago.

06-25-11, 12:50 AM
The pressure sensor is the most likely cause, but you don't know what was done to the car before you got it.

06-25-11, 05:10 PM
If the oil pressure light doesn't come on any other time it could just be the low idle and load from the air conditioning being on. Some cars have a switch to kick up the idle when it is on, if it doesn't have that the idle speed could just be set too low. Or maybe there really is a oil pressure problem.

06-26-11, 09:29 PM
well idk know i replaced the pressure switch and no light now, but today was 97 and when i came outside this afternoon, my car started making a slight tapping/ ticking noise. my first thought was the lifters but after a short period the noise went away and never heard it again for the rest of my drive to work. idk i really dont want to have to do a complete engine rebuild!

06-27-11, 09:32 AM
I stand corrected then! :)

Thanks for clearing that up guys... information much appreciated.

-- AJ

06-27-11, 11:36 AM
well idk know i replaced the pressure switch and no light now, but today was 97 and when i came outside this afternoon, my car started making a slight tapping/ ticking noise. my first thought was the lifters but after a short period the noise went away and never heard it again for the rest of my drive to work. idk i really dont want to have to do a complete engine rebuild!

What weight oil are you using?

06-27-11, 01:07 PM
10W30 high mileage mobile 1 oil. K&N filter. i know that the heat can play a role in the viscosity of your oil, but i shouldnt have to change to 20w just to keep the oil pressure up.

06-27-11, 05:50 PM
At anything above freezing, 10w30 and 20w30 are identical ("w" mean "winter"). Switching to 10w40 would be advisable, just in case there is excess clearance in the bearings.

07-01-11, 05:44 PM
ok so heres the update. the dang light started coming back on again and im like oh no here we go again. so i take it to the shop this time and had them do a real oil pressure test. the call me 5 hours later and say that i have a worn bearing. at first im like yea sure i do but then i was like why would they tell me something that they dont even fix? so i start thinking about rebuilding the engine and so forth.well today was another hot day mid 90s and i ran the ac on the lowest setting(60) for the entire day going to and from places running errands and guess what!! no light no noise just a slightly lower idle. the car even wasnt as sluggish as it was before with the ac on. so now idk if its even a problem anymore cause the engine runs fine all of a sudden. im still going to change the oil to 10w40 just to be safe.

07-01-11, 08:11 PM
Get another shop to check it but chances are you've got low oil pressure yeah worn bearings will cause that. Rebuilding the engine can cost more then the car is worth. You might be better off just getting a used engine instead.

07-01-11, 08:16 PM
yeah thats what im going to do. hopefully this engine holds up long enough for me to save the money to do the swap. speaking of which how difficult would you say it is to convert over to like a LT1 engine? i kinda want to get a little more HP as well as the nice throttle response from a FI car.

07-01-11, 08:36 PM
The LTI is port fuel injected, so you would have to get the entire computer control system and wiring harness. It wouldn't be too difficult, but it can be messy with all the wires.

It would be a little simpler to get an L05, which uses TBI and can be converted to run with a carburettor. The TBI engine doesn't use as many sensors and if build it with a carburettor, you can delete the computer entirely.

Either way, you need the transmission, drive shaft, and differential. If you want to keep the engine fuel injected, you will also need the gas tank and fuel pump.

07-02-11, 02:05 PM
TBI sounds easier, but thats seems like a lot of things that need to be changed. idk maybe a crate 350 will be cheaper than converting all those things. thanks for all the info guys im going to take some time and figure out what exactly im going to do.

07-03-11, 01:15 PM
There's no real difference going to either type of fuel injection. It comes down to getting the wires to the computer and giving it power. If you are going to do that I would get a whole car for parts that runs. You'd get everything you need in one shot. It is probably easier to use an aftermarket computer setup to get it running.