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Regulating your idle speed

I can remember back when I was in HS and my first car was a early 70’s Maverick. I can remember that I could via the carburetor regulate the idle speed on the car. My question is now with the new modern car, is it even possible to regulate your idle speed or is that all controlled by the computers and can those be adjusted?

Also on my newest car I have a oil PSI gauge. For me this is the first car to have that gauge? Exactly what is it showing and when at idle where should the gauge be reading?

If we knew what year make and model you currently have we could possibly guide you to idle adjustment procedures. Some vehicles this is easily done, while others it is a computer affair.

Again, in order to answer the Oil Psi question we need the vehicle info. What it shows is the oil pressure obviously. It will register higher pressure when the oil is cold and thicker…it will drop when hot… The parameters are vehicle based… My VW has Oil psi of 100 at idle upon startup and 80psi when hot…which are high numbers, in fact the highest of any vehicle I have ever owned, but it is perfectly normal and healthy. Your numbers will differ…

My V8 cold-starts at about 50 psi and settles down to about 40 psi and hot idle and 46 ish at higher RPM. The gauge is showing the pressure of the oil that keeps your engine bearings flooded with lubrication. Pressure is required to float the crankshaft on a film of oil. More rpm means more pressure, and good thing, more rpm means the engine needs more pressure.

Generally with computer controlled cars the idle is adjusted with the computer (ECU). There are plug-in devices that can adjust that idle speed by downloading a new calibration to the ECU. Unless you are modifying the car, there is no reason to adjust it. If you idle is out of spec, it is likely the throttle body needs cleaning.

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I’m sorry I left that out. Presently I own a 2011 Cadillac CTS 4 with the 3.0 engine with about 86000 miles on it. Presently my car at warm idle is around 500 RPM and the PSI oil gauge hovers around the 25 mark on either side of it kinda depending on outside temp from what I see. On cold start up it’s up over 50+ and then what seems like “stages” as the car warms up goes down to just below 50 then down around 40’s then finally when fully warm around the 25 PSI mark.

My car will rev will high on first cold start of the morning for a few moments, then calm down and then decrease slowly as the car warms up.

Your car is donig what it’s supposed to do except it seems that 500 RPM is kinda low. Check the specs out on that idle speed, clean the throttle body and idle air control system and if necessary adjust the base idle speed. There is a screw similar to the one on carburetors for adjusting the idle speed. But it’s likely that cleaning the system will bring everything back to normal.

As a general rule, as long as the oil pressure stays above 15 psi, you should be OK. As an engine wears out, the oil pressure tends to drop because of increased clearance in the crankshaft bearings. Most oil pressure idiot lights don’t come on until down around 10 psi or lower.

As for the idle speed. On the side of your throttle body is a device called an Idle Air Control, aka IAC. It is a small valve with a stepper motor that opens and closes the valve. With your foot off the gas, the butterfly (throttle plate) in the throttle body should be completely closed so that the IAC controls the amount of air that gets into the intake manifold.

The IAC stepper motor is controlled by PCM (powertrain control module, aka the computer). But it only controls the IAC when your foot is off the gas. It gets the information that your foot is off the gas from the throttle position sensor (TPS) in older cars, usually pre 2006, or from the accelerator position sensor on the gas pedal in newer vehicles with “fly by wire” throttles.

The throttle body has a throttle plate stop screw that resembles the old idle adjustment screw on carburetors. It is sole to prevent the butterfly from closing too hard and damaging the soft aluminum throttle body bore. On older models, sometimes someone would “adjust” this screw to “adjust” the idle speed and end up making it look like the driver still had their foot on the pedal to the TPS. When conditions changed, like temp or barometric pressure, the idle would change, sometime too low to keep the engine alive. There would be no code or CEL (check engine light) because the PCM did not know that the screw had been changed. I’m not sure if someone fiddling with this screw would have the same effect on fly by wire throttles.

Dashboard tachometers are not precision instruments.
If you’re concerned about idle speed read it on the OBD-II port.