Auto trans idle fine in P or N but RPM drops when in D. WTF!

[Alex0607]

Is there no answer to this dreaded issue? Seems like alot of auto transmission have this problem. RPM doesn't just drop but whole damn car would vibrate. And this occurs at times and other times its fine. Something is definitely up with this.

People have mentioned it could be the Torque Converter, dirty ICV, dirty MAF, bad coil, bad spark plug and etc.

How many people here have the same issue and still haven't solve their problem?

[ElleShooTiger]

How many rpms are we talking about here? Putting a transmission into any gear adds a load onto the torque converter, thus slowing down the engine by a few hundred rpms on most cars.

If you are getting vibrations with the trans in gear, start checking your engine and trans mounts

[Alex0607]

HI ElleShooTiger,

Thanks for your response. I did a few more things today. Checked the battery and it seems to be on its way out. So replaced that and this is what I noticed.

1. When aircon is on and in gear, car RPM dropped from around 650-700 to around 600.
2. When aircon is on and in neutral or park, the car RPM is stable and no vibration.
3. When aircon is off and car is in gear, no vibration and RPM stable at around 650-700.

So seems like when 2 things happen, the load seems to be too much for the engine to cope. Whereas either one is on, the car is fine.

Would this be considered normal? Just that my other 2 automatic bimmers seem to be stable in terms of RPM when the engine is loaded with aricon and in gear.

But I definitely will look into what you suggested. i.e. transmission and engine mounts.

Thanks once again.

UPDATE: Drove the car to the mechanic today who is currently working on my E46 and had him look at my E60. He said the engine mounts need replacing. So will do the tranny mount as well. Showed him what happened when the aircon is on with the car in gear and vice versa and he suggested it could be the ICV controlling the aircon as the aircon seems to be the one causing the drop in RPM. So fingers crossed he will be able to identify the cause and fix it. Looking good....

[Alex0607]

Brought the car to a friend who has a Bosch scan tool. Turns out there is a setting for the idle when the aircon and gear is engaged. Default setting on my car was 0. So we upped the figure to 50RPM extra and now no more vibration. Feel like adding a bit more RPM to it though. 50RPM extra still seems a bit low. Might add another 25RPM the next time I have it scanned.

[White94RX]

Yeah, I was going to mention that the low idle speed causing the vibration is a very common problem/complaint we get from customers. Simply raising the idle by 50-100 RPM almost always solves the issue.

I think BMW put out an SIB about the rubber dampener and bracket on the exhaust, but it's just as easy to raise the idle to smooth it out.

[pcy]

Does any one know if NCSexpert software can be used to raise the idle speed setting?

[Alex0607]

If the setting can be done by the dealer, I think its worth it to have it adjusted. the idling issue is very annoying and unsettling at the same time. Almost to the point of not being able to enjoy driving the car.

But I had the dealer replaced a few parts in the engine bay and I told them specifically what the problem was but their mechanic still overlooked the idle setting. I don't get it. Either they are just plain lazy or not sure what to look for.

[pcy]

Increasing the idle speed is actually the solution to the problem or just masking the underlying problem?

[Alex0607]

No idea. I was thinking the same about it being a symptom as oppose to the cause. But it seems to have solved it. The fact that there is a setting for RPM increase in the diagnostic tool showed that the rpm was not set properly for when Gear/Aircon are engaged (range allowed was 50-150rpm increase). There were 4 settings as follows.

1. When in Gear: set to 150 as default
2. When aircon is on: set to 150 as default
3. When in Gear/aircon on: 0 as default
4. When battery voltage is low: 0 as default

We just went and increase the rpm by 50 for the 3rd option and saved that into the ECU. After starting the engine and putting the car in gear and aircon on, no more vibration and the idle rpm did not reduce.

[hitmandmc]

Alex...Can I do this change with my obd2 cable? I have K+DCAN one.

Thanks!

[Calicoastin]

What software (DIS,SSS,NCSEXPERT) can be used to adjust this setting?

[hitmandmc]

What software (DIS,SSS,NCSEXPERT) can be used to adjust this setting?

I didn't found any of these options with ncs

[Alex0607]

Hi, very old thread but I am sure most people have resolved their problem. To answer hitmanmc question, I guess you can as long as the software has a setting for adjusting the RPM level. The Bosch tool has it which cost thousands. My $100 plus diagnostic doesn't.