Should the accelerator work like this?

[TDot]

While testing my brakes I finally narrowed down where the accelerator has the most hesitation. It seems when you make a sudden full stop from a relatively high speed (50-60), and the immediately press on the accelerator the car simply revs for a second like something isn't engaging and it doesn't know where to lock up and move; then all of a sudden it jumps like a frog. This happens time after time. It seems like something is going to break. Can anyone verify this with their M?

[svard75]

Definitely not normal. That is an early sign of transmission failure. When did you change the transmission oil last? Transaxle oil? Do you drag race? Pop the lever from n to d while in high rpm? Slow engagement could be worn bands or gears. If you tow stuff often without an aftermarket cooler for long periods of time. Sudden stopps often also puts excessive strain on the torque converter. If the oil gets above 300 degrees its not as effective.

[TDot]

Never changed transmission oil...never transaxle oil...no racing...no popping levers...no towing.

[EniGmA1987]

Transmission oil needs to be changed , as is the case with just about any oil. Probably best to do a drain and fill only right now, then after a 500-1000 miles from the oil chance go to a mechanic or dealer that has proper, modern transmission flush equipment and get the transmission oil fully flushed and changed. The first time is just so you have new oil and to get any sediment and other junk out of the transmission that is sitting in the oil. Then once you know everything is still working good do the proper change that will get almost all of the junk that is loose or somewhat loose inside the trans out.

[The00Dustin]

Sounds normal (albeit not optimal) to me. I've been experiencing similar irritations with for 5 years / 120,000 miles through transmission flushes and fluid changes on my 06 M45 that now has over 160,000 miles. My experience may not be the same as yours, though. For instance, I believe one experience is because the transmission downshifts when you are decelerating and then won't shift up for a few seconds because it just shifted down, however, that particular experience doesn't necessarily involve a complete stop (and certainly doesn't involve sitting at a complete stop for any amount of time at all). The other experience involves sitting at a complete stop, and them moving your foot very quickly from the brake to the gas. The gas doesn't have to be pressed hard, just pressed quickly, and it's almost as if the rev limiter (for when the brakes are engaged, as opposed to the rev limiter for taking out in general) is still engaged because it thinks the brake hasn't completely disengaged yet. It sounds like you are experiencing this, but pressing the gas hard, causing the "jump like a frog" when the system decides the brake has completely disengaged. I have also always noticed a few other irritating but not directly related behaviors that lead me to believe the ECU (and/or other CPU and/or CAN) is simply too slow or checks things in an illogical order. For instance, if I have ICC on but not engaged, and then set it to 55 while driving 60 behind someone else driving 60, it will switch between accelerating and coasting a few times before it gets down to the set speed like it is trying to keep up with that car (even though ICC should only accelerate to keep up with a car ahead of you when that car is driving lower than your set speed). I won't go into anymore detail, but your experience sounds more like programming than a transmission problem to me. Nonetheless, perhaps it could cause one, and maybe you should adjust your driving to prevent that (because I don't know how to reprogram the computer or hack the sensors to prevent it). If your brakes are soft, bleeding / flushing them might even help if I'm right about the root cause, but I don't think the behavior will completely go away, because I suspect it is due to design.

[TDot]

Just to clear up (during my very brief tests of doing this 4x on the way home) I didn't come to a complete immobilized stop, more like I hard braked from a high speed to 1-4mph, then stepped back on the gas hard immediately since I was still in a little traffic. I'm going to see if I can try my boy's cars to see if this is reproduced.

I do have that same issue of stopped at the light and moving to the gas quickly. But that is more sporadic and isn't as "scary" as this...seeing the car rev up to 2.5-3k and sounding and feeling like you are literally in neutral, then BOOM, you take off.

[svard75]

Dustin. The CAN system is basically a computer network. Its very fast. The fact that we are drive by wire and once he hits the gas the engine revs tells me its responding to input. An auto transmission is driven mostly by vaccuum from the intake manifold and solenoids. Im betting more on the oil being the culprit with possible blocked valve. However i wont completely rule out the ecu. It could also be a safety mechanism to prevent sudden gear changes.

Start with a fluid flush. Then visit an uprev tuner :-)

[EniGmA1987]

The CAN system is basically a computer network. Its very fast.

No, it is actually incredibly slow. Max speed is only 1 mbit. Each device on the network uses multiple bits for their own ID and data transmission too, so it is not like a sensor only needs to send a single bit. Then it would be really fast, but since we have hundreds of sensors and computer chips all sending data each frame that is over 1 byte long per device, the system has a pretty slow response time.

[svard75]

The CAN system is basically a computer network. Its very fast.

No, it is actually incredibly slow. Max speed is only 1 mbit. Each device on the network uses multiple bits for their own ID and data transmission too, so it is not like a sensor only needs to send a single bit. Then it would be really fast, but since we have hundreds of sensors and computer chips all sending data each frame that is over 1 byte long per device, the system has a pretty slow response time.

Surely 1Mbit should be fast enough to send data from the ECU to the TCM and back again. I guess it depends on how many frames it has to send and what other messages are being sent. Further discussion regarding this I am going to digress since I am not an auto technician and can't comment on this level of analysis.

TDot how many miles on your car?

[TDot]

84K.

[svard75]

Okay so I just performed the following. Driving at 45 mph. Brake to 0 so hard my belts pulled me back then stepped on the accelerator. No hesitation at all. Immediately began to accelerate. My ecu is uprevd and the torque management tables are tuned but I still think your symptoms are unnatural. 84k is not hugely overdue but 60k is standard. Try that first. Did you go in for the accelerator pedal recall?

[TDot]

Don't hit the gas at a dead stop, stomp on it just before the car stops moving (1-4mph) and quickly (I don't know if that really matters, but that's how I was consistently reproducing it). And take the car up to 55 for good measure. I don't want to do this anymore because I have to take a road trip in a week and don't want to put undue strain on the transmission if in fact that is what's going bad. Don't want to end up stranded far from home. I'll be back to this in two weeks to figure this out and get it fixed.

Yes I got the pedal "fixed".

[svard75]

Ill give that a try tomorrow. Going on a long trip with old transmission oil could also be a recipe for disaster. Last time I drove to Florida I changed all fluids just in case.

[The00Dustin]

I had the accelerator recall performed and I still say this sounds normal (as in due to design, as opposed to by design). Certainly won't hurt to do some transmission maintenance, and if it helps, that's great, but again, an experience of mine:

When coasting to a stop and starting to brake because getting close to the light, then the light turns green and I go to the accelerator (quickly, but not harshly). The engine revs and then acceleration kicks in after the fact. In my case, I may be going more than 1-4 mph, as the revs just seemed like first gear RPM levels, but I'm not driving aggressively at all, and I assume TDot is (so the RPM levels may match where my foot is on the pedal with the transmission between gears [I won't say in neutral because I don't believe the programming is THAT poor]). That having been said, again, there are slight differences in my experience, so TDot's experience may be a symptom of a problem, especially if it hasn't always been that way. Even if it is "normal" it may slowly cause damage, and I would certainly be concerned myself if I was experiencing it all the time, but since I normally don't drive that way, when it happens more like he describes on rare occasion when I am driving more aggressively, I don't worry about it, I just say "stupid car" (sometimes under my breath, sometimes aloud) and keep on keeping on. Then again, I know people with Jeep Grand Cherokees that down shift a second very hard downshift climbing wimpy hills, and we live in hill country. Their transmissions are have as many miles as mine and no problems (probably with less maintenance), so maybe it's no big deal for a transmission made for a Titan to experience that jarring (assuming the M35 also has that transmission).

Hopefully Svard can reproduce and get a better idea of what is being felt.

[svard75]

Performed the following a few more times without success in reproducing your issue.

Driving at 55MPH brake hard to just under the last marker before the 0 then quickly accelerated and still did not notice the rev. I did this 3 times.

I then switched to manual mode and drove through the gears at normal speeds 40-45MPH. I was in 4th then slowed down quickly and slowly enough right until the display change to 1 then quickly stomped on it. I did notice a very slight rev till about 2.1K but that is normally the RPMs that the torque converter kicks in. After 2.1K it immediately began accelerating. Almost unidentifiable because the car is still kind of rolling slightly. If you try this in manual mode and are experiencing much greater RPMs than 2.1K then I would point to the oil being bad or the stator not functioning quickly enough (likely due to insufficient oil or bad oil). Perform a transmission fluid exchange if you can find someone with a low pressure system. You need to get the clean oil in all the passage ways so it pushes the old stuff out. Typically they should tap into the transmission oil cooler lines. Hope this helps.

[The00Dustin]

Since I have an M45 and not an M35x, I'm going to assume that our behavior is different and only sounds similar. The only other way I can see them being similar at this point is if an ECU reset would help, but I don't know the procedure (nor where to find it on this forum, though I know it's here somewhere), and the accelerator pedal recall included an ECU reset, so I don't see that helping. Nonetheless, the manual mode test sounds interesting, and a transmission fluid flush certainly shouldn't hurt.

[Six_Legs]

Since I have an M45 and not an M35x, I'm going to assume that our behavior is different and only sounds similar. The only other way I can see them being similar at this point is if an ECU reset would help, but I don't know the procedure (nor where to find it on this forum, though I know it's here somewhere), and the accelerator pedal recall included an ECU reset, so I don't see that helping. Nonetheless, the manual mode test sounds interesting, and a transmission fluid flush certainly shouldn't hurt.

ECU reset is a sticky on front page of this forum under How to and FAQ...
Did the reset last week and it worked. It took 4 tries, timing is important!

[TDot]

Since summer is coming up I decided to revisit this and put some money on the side and rebuild a transmission sometime in the middle of spring. I was talking to a mechanic, a guy generally trust, and he said this has absolutely nothing to do with the transmission in his opinion. He believes it's a programming issue and I should uprev it and i shouldn't see this problem again. he pretty much reiterated what The00Dustin said almost word for word basically the problem is the car was at a high rate of speed... In a different gear... And if I break and then try to accelerate again the car still thinks it's in the higher gear. Cheaper than getting the transmission rebuilt.

Thoughts?

[Brian35XR]

I don't have advice but I just want to say my transmission has this exact behavior. When slowing down from a high-ish speed if I take my foot off the break and immediately give it gas (like in stop-n-go traffic in the city), the engine revs up a lil bit then slightly kicks forward. It's definitely not a harsh kick but it still bothers me.

What bothers me even more though is something else my car does .. If I'm cruising along at a decent speed (maybe 3rd gear) and I take my foot off the gas, it seems like my car immediately wants to start downshifting through ALL the gears till eventually it comes to a slow crawl. My other cars before this seemed like they could coast much longer but this car wants to just slow down right away.. Is this normal? Does your car do this?? Drives me nuts!!!

[The00Dustin]

What bothers me even more though is something else my car does .. If I'm cruising along at a decent speed (maybe 3rd gear) and I take my foot off the gas, it seems like my car immediately wants to start downshifting through ALL the gears till eventually it comes to a slow crawl. My other cars before this seemed like they could coast much longer but this car wants to just slow down right away.. Is this normal? Does your car do this?? Drives me nuts!!!

I recommend you peruse this thread.

[Brian35XR]

What bothers me even more though is something else my car does .. If I'm cruising along at a decent speed (maybe 3rd gear) and I take my foot off the gas, it seems like my car immediately wants to start downshifting through ALL the gears till eventually it comes to a slow crawl. My other cars before this seemed like they could coast much longer but this car wants to just slow down right away.. Is this normal? Does your car do this?? Drives me nuts!!!

I recommend you peruse this thread.

This was my thinking too however I've never had a car that engine braked this drastically so I just wanted to make sure everyone's car did the same... looks like they might've changed this behavior in 08+?

This and the ultra high revving on the highway are definitely my two biggest gripes about this car.

[fat3oy]

Is it not as simple as RPMs when hitting the gas? Just curious - if you brake hard, hit gas at top of RPMs, it will automatically shift quicker than if you had completed a shift and have to run back up to WOT shift point...

[Blackzilla]

I'm having this exact same problem it's only happened a few times. I'm going to do a drain and fill of the transmission fluid then a flush like suggested. Did this problem ever go away for you?

[TDot]

Just did a transmission flush and It seems to have remedied everything. If it's just a placebos affect I'll update in a couple weeks.