The issue that urged me to bring the Infiniti G37 to the dealership is fault code P0507, (high idle condition) where the engine idles at about 2,000 RPM, (normal idle is 650 RPM). I firmly believe this condition initiated while trying to start the vehicle with it's battery having a very low charge. At that time, the engine made several slow revolutions, (about three) before comming to an abrupt halt. I believe during this failed attempt to start the engine, the Throttle Body Electric Servo Motors suffered some damage or were otherwise thrown out of synchronization due to a low voltage signal. It is also my belief, the damaged / out of sync servo/s will not, (according to diagnostic tools), accept the "Idle Re-learn process". I also suspect the diagnostic equipment, (and therefore Infiniti Technicions), are unable to ascertain the reason for the initial fault.

I previously took the car to a different Infiniti dealer where the mechanic did the initial diagnosis he stated; "It will not re-learn the idle setting", I was subsequently advised by Customer Service, "The mechanic did the wrong test on the wrong size engine". I was utterly astounded by this. The "Trained Professional" at the Infiniti Service center conducted the "wrong test on the wrong size engine". The end result: To correct the condition and re-learn the idle, I was advised a new ECM was required. Now having lost all confidence I declined further service.

After conducting additional research, I located a firm that would, (utilizing the VIN# and security information), supply a reprogramed ECM. I replaced the OEM ECM with a reprogramed unit, (fault code free with all security data cloned). After replacing the ECM, the high idle condition remained and normal idle could not be re-learned.

I then replaced the "new" ECM with the original ECM and contacted another Infiniti dealer hoping for a more accurate assement . The result was essentially the same, I was advised the idle could not be re-learned and a new ECM was necessary.

I'm certain the Infiniti technicians are trained and adept at conducting diagnostics however, conversing with the technician leads me to believe they are willing to simply acceptance the readout / results from the diagnostic laptop screen and less able to give thought or perspective to events precipitating the fault code.

During my discussion with the Infiniti technician, he stated "The brake pedal is hard and needs a booster" I tried explaining to the technician the performance of the brake booster is contingent on the level of manifold vacuum pressure which is greatest during closed throttle position. Since the problem with the subject vehicle is "high idle condition" the throttle valve is in a (Part Throttle Open) position, (i.e. akin to having one foot on the gas pedal trying to drive at 30MPH and the other foot on the brake). Thus under a part open throttle condition, sufficient manifold vacuum pressure is not generated to support all the vehicle's systems requiring negatitive pressure, (including the brake booster). I do not believe the technicion understands this fact.

My question to the Customer Service person, "What if the ECM is again replaced and the condition is not rectified?" The response was; the cost of the new ECM would be refunded and the OEM ECM replaced, (sounds to me like "trial and error")

Lacking confidence replacing the ECM will resolve the problem, I'm currently left with conducting additional research and verifying the condition of the Throttle Body servo motors.

I'm a retired Director of Engineering and a former mechanic servicing motorcycles, autos and diesel trucks. I have a wealth of knowledge on many aspects of engines, drivetrains, brake systems etc., but this high Idle Condition has stumped me.

Does anyone have any input or had a similar condition?

Sounds like you may actually have a hidden vacuum leak(probably a punctured diaphragm in the brake booster from what you describe), but one thing is certain, IAVL positively will not execute unless the RPM can be dropped below about 900. The usual work-around for that is to pull either injectors (preferred if handy) or coils one at a time until the idle drops far enough for the procedure to complete. First check your STFT with a streaming scanner, if it shows lean at idle (positive more than 10%) but normalizes substantially when you raise the RPM's to 2500~3000, then you definitely have a vacuum leak.

Just an FYI, with no load engine vacuum drops very little when RPM's are increased below about 25% throttle, you only see a momentary drop when the plate moves. That generally shouldn't affect the booster. In addition, the booster has a check valve that will maintain a reserve of vacuum to support several brake cycles even at WOT. So if a 2000 RPM idle is affecting your brakes, I smell a rat (and metaphorically, it probably ate a hole in your diaphragm).

I believe the brakes are function completly normal. The mechanic was obviously not accustomed to stoping a vehicle with the engine running slightly above 2K RPM, (he said "I have to push hard on the pedal"). No kidding, the car is trying to go 30MPH! If the trani is shifted into neutral, only slight pedal pressure needs to be applied to stop the car. I checked thoroughly and there are no vacuum leaks.

I tried disconnecting two injectors, (threw a code on the ECM) and still no luck to re-learn the idle.

I remove the air intake tube from the left bank throttle body while the engine was running, (bypassing the MAF throwing another code), and simply pushed down on the lower half of the butterfly. The engine RPM dropped immediately. I did not look at the tach but the RPM drop seemed to be the normal idle speed.

I'm positive the issue percipitated when trying to start the car with a nearly dead battery as I heard an unsual sound eminate from the top of the engine, (not a solenid clicking as is typical with a low charge battery). The condition of the high idle started immediately after jump starting the car.

If forcing the butterfly shut dropped the idle then either that butterfly is sticky (the motor operates to open it, return is via a spring) or the sensor in that TB is way off from the "default" map in the ECM. The latter would make sense with a jumpstart, since that could corrupt the ECM's data memory. It would also make sense with it not accepting an IAVL. You could cross-check the TPS voltage readings from the other TB, if the left is way off from the right then you may have a bad left TB. Two other things about IAVL's that they don't mention in the FSM, it won't take if 1) the tranny isn't warm, or 2) the ECM settings for "Target Idle" or "Target Timing" have been altered from zero.

Thank you for the information.
I thought the voltage feed to the TBs is a Squarewave. In order to correctly monitor the squarewave signal, I think a oscilloscope would provide an accurate rendition of the potential and wave lengths.

I ordered a used left side TB, (suppose to be tested and functional). If after swapping out the TB, the ECM default is incorrect then the idle will remain high. If the OEM TB is defective / out of sync, and the replacement part is functional, (the ECM default correct), the idle should drop.

I would think the TB's butterfly resting position, (engine off / key off) should be closed, (or nearly closed). Currently the butterfly on the TB, (engine / key off) can be physically, (easily) moved to a more closed position.

I had remove both TBs and although they were not loaded with carbon, I throughly cleaned them, (it made no difference whatsoever in the engine idle).

superchicken wrote: ↑

Sat Aug 27, 2022 3:56 pm

I thought the voltage feed to the TBs is a Squarewave. In order to correctly monitor the squarewave signal, I think a oscilloscope would provide an accurate rendition of the potential and wave lengths.

It is, but it's a push-pull PWM that works against spring pressure.

superchicken wrote: ↑

Sat Aug 27, 2022 3:56 pm

I ordered a used left side TB, (suppose to be tested and functional). If after swapping out the TB, the ECM default is incorrect then the idle will remain high. If the OEM TB is defective / out of sync, and the replacement part is functional, (the ECM default correct), the idle should drop.

That sounds like a plan.

If it accomplished anything, swapping the throttle body, (which made no difference in the high idle condition), leads me to believe the throttle body components are not the problem. The vehicle has 57K miles and since the high idle condition occured only after trying to start the engine with a very weak battery then jump starting, I suspect some sensor or something in the engine management system was affected.

I could trust the Infiniti dealer and pay over $2.0K to install and reprogram a new ECM however I doubt that is the issue. The feeling I get from the dealer seems like "trial and error" as they can provide no assurance the new ECM will resolve the problem.

The gods were with me. After removing the used throttle body and installing the original unit, I tried again for at least the tenth time to re-learn the idle settings. The re-learn was successful. The only different parameter during this re-learn process and the previous attempts, the car was sitting level. On previous attampts the car was on my driveway ramp that leads into the basement heading down hill, (apx 25 degrees).

In any case, two Infiniti dealers, (the experts), could not resolve the problem. Both dealers recommended a new ECM, ($1,850.00).

The Infiniti mechanics don't research / consider the root cause, they respond to the computer's results.

UPDATE: Throttle Relearn Steps that are easier to follow and may cure your CEL Code #P0507 (High Idle).

These steps should work on your Nissan or Infiniti.

Follow these throttle relearn steps exactly as written below:

===> Turn off all loads like the AC and lights and other accessories if any.

1. With a cold engine..
2. Make sure the front wheels are straight ahead and everything is off, I.e. Radio, lights, wipers, heater, etc.
3. Shut the engine off, waited 10 secs. This resets the butterfly-closed position.
4. Turn the key to on, waited 2-3 secs
5. Turned the key to off, waited 10 secs. This resets the butterfly-open position.
6. Turned the key to on, waited 2-3 secs

===> Drive the car sufficiently to reach normal operating temperatures. Park it, and keep the front wheels straight ahead, loads off... and follow these steps:

Note: If you don't see your CEL blink in Step #3 below, then you will need to repeat these steps and pay closer attention the time as counted down on the stop watch.

1. With enging running, turn the key-off and wait 10-15 secs.
2. Turned the key-on, start a stopwatch immediately, and at the 3 second point… STOMP on the accelerator (quickly) 5x and release.
3. When the stopwatch reaches the 15 second point… STOMP-AND-HOLD the throttle pedal to the floor until the Check Engine Light (CEL) starts to blink (around 20 seconds typically).
4) When the CEL stops blinking (in about 5-10 seconds)… release the pedal and immediately START the engine.
5) Let the engine idle for 10 seconds and then rev-up the engine twice.
6) Turn off the engine and wait 20 seconds and you are done.
7) Restart the engine and confirm your idle is remains stable at 650RPM.
End.

If you have a OBD2 test device that will clear your DTC codes you might also consider following these steps to reset your fuel trims:

Instructions
1) Start engine and warm it up to normal operating temperature.
2) Turn ignition switch OFF.
3) Disconnect mass air flow sensor (MAF) harness connector, and restart and run engine for at least 3 seconds at idle speed.
4) Stop engine and reconnect mass air flow sensor harness connector.
5) Make sure Detected Trouble Code (DTC) P0102 is displayed.
6) Erase the DTC memory.
7) Make sure no codes are stored in the ECM.
8) Run engine for at least 10 minutes at idle speed.