454 CID doesn't have this problem an 86 CID engine sure does, alternator rated output is 120 amperes, but only capable of producing this kind of output with an engine speed of 2,500 rpm. When these small displacement engines were introduced, some form of idle speed control had to be added.
Typical was an IAC idle air control valve, simply a valve that would let more air bypass the throttle body, but the Cruze uses throttle by wire, so the IAC is not needed, throttle valve is opened by the BCM for idle boost.
Wondered about this in particular with the PCV returning back to the input of the turbo, as the engine wears most blowby in the piston rings, more crap returning back through the throttle body vane with soot that can hamper its movement. So it can be receiving commands to open, but stuck. Fords really had this problem returning the PCV to the air cleaner that would retard the vane in the throttle body. Honda's were far more intelligent to return the PCV to the base of the throttle body.
In this respect, consider TBW another PITA, can put your fingers on the linkage to feel if the vane is sticking, and this is not the easiest TB to remove for cleaning, but can peek in there to see if you have soot in there. Carbon is the problem, been this way for over a hundred years, builds up on the piston rings and even locks them so they can't expand anymore.
One reason why I am treating my vehicles frequently with Seafoam, not going to get into what kind of carbon cleaner is the best. But the way the Cruze is set up, can also cause the TV to get sticky that may well be the cause of your problems. How many miles on this thing?
There is a learn procedure for idle boost in the Cruze, goes like this.
"Throttle/Idle Learn
The Idle Learn Procedure listed below must be performed whenever the following occurs:
The crankshaft position variation learn procedure is also required when the following service procedures have been performed, regardless of whether or not DTC P0315 is set:
- The throttle body assembly is replaced
- The throttle body is cleaned
- The engine control module (ECM) is replaced
- The idle air control valve is replaced
- Power disconnection (battery cable, ECM fuse, etc.) (Delphi ECM only)
- Turn the ignition ON.
- Turn the ignition OFF for 15 s.
- Turn the ignition ON for 5 s.
- Turn the ignition OFF for 15 s.
- Start the engine in park/neutral.
- Allow the engine to run until the engine coolant temperature is greater than 85°C (185°F).
- Turn the A/C ON for 10 s, if equipped.
- If the vehicle is equipped with an automatic transaxle, apply the parking brake. While pressing the brake pedal, place the transaxle in drive for 10 s.
- Turn the A/C OFF for 10 s, if equipped.
- If the vehicle is equipped with an automatic transaxle, while pressing the brake pedal, place the transaxle in park/neutral.
- Turn the ignition OFF. The idle learn procedure is complete."
For extra protection on the alternator output, a current sensor is located in the negative battery cable that will limit the maximum duty cycle of the field current. For the most part, I find rear window defrost to be next to worthless, so use a scrapper, this adds another 25 amps to the alternator load, electrically heated seats are also hungry, blower with AC pulls another 20 amps. Alternator can handle this at 2,500 rpm, but certainly not at 600, radiator fan is also hungry.
But your idle speed should hold even though with all this stuff on, will be drawing the excess current from the battery, and this is the worse time as your battery just had a starter load on it. Could sit in your car in neutral and hold the tach at 2,500 rpm until it warms up, or just switch stuff off. With an AT, have to be a low idle or will really stress your torque converter. That fluid is ice cold.
