Did he check all the grounding straps

 

To be honest I wouldn't know where to start on the grounding straps, could you point us in the right direction.

 

There are like 4 of them spread out on chassis and firewall

 

Think you could grab some pics of the locations??

 

Exact same issue:
500 in drive and rough
650 in park, neutral and reverse
Sometimes, no rhyme or reason, it idles at 650 in drive.

Rough idle seems to be related to engine speed - if I slightly depress accelerator to get to 650 in drive it's smooth. Never had another vehicle do this as the computer should regulate to the same RPM regardless of load/temp.

Seems to be a fairly widespread issue and no one has a resolution.

-Eric

 

Hi Eric & All:
Yup, this is the exact same characteristics as mine. So I am back from vacation and I got my car back on Saturday. I spoke with my mechanic at length regarding this issue. I wanted him to check over the entire vehicle to make sure everything was ok. Everything checked out just fine. There were no issues with the engine or tranny mounts. No hose issues, no issues with the alternator, no issues with the belt or tensioner. He checked the driveshaft and also the exhaust system and everything was fine. Everything is bone-stock on this vehicle too. He said he may have felt what I was talking about, but it was very minimal and said it just may be a characteristic of the car. He also said when he had the car (for a whole week) the rpm never dipped to 500 rpm. I told him then he didn't feel anything. He advised me to keep an eye on it and to bring it to him when the vibration occurs and he will take another look. I might arrange to to directly to his shop after work some day when the issue is occurring, so he can get first hand experience. Now, the only service items I performs BEFORE dropping the car off to him was: 1) replaced K&N "stock style" air filters with OEM. 2) cleaned MAF sensors. 3) Cleaned throttle bodies. The vibration was still there.

What I'd like to know is: Why does this occur in Drive (D), but not in Reverse (R) ??? Also, it's clear that whatever is happening is intermittent, but is always directly related to engine RPM.

My next step is to contact Infiniti and see if there are any ECM and/or TCM updated that need to be performed. My car is a 2015 Q40, so I figure it will have all the latest updates, etc., however, you never know.

Here's an interesting question: Are there any owners out there that do NOT have any issues with low RPM in Drive (D)? At the same time, are there any owners out there that have 500 RPM in D, but absolutely no vibration?

JSB

 

A few ppl have reported this exact issue...any chance you discussed with your mechanic the possibility of the belt tensioner going out as Surfnazi mentioned a few posts up?...if the bearings are going on the tensioner I would imagine the issue might be more apparant once the car is driven further and they get hotter...maybe your mechanic didn't drive it as long as you do so they didn't get hot enough to cause the issue?...just throwing this additional speculation into the mix as I am genuinely curious about this issue given the number of reposts and nooneever posting a resolution, and Surfnazi's mention of the tensioner is the first I've seen of anyone suggesting it as a possible source

 

The OP stated his mechanic look over the belt n tensioner.

 

I called my local Infiniti dealer about the issue. He said the checked the common issues/complaints board and doesn't see anything regarding the symptoms I stated. He did ask if the throttle bodies had been cleaned (which they were) and whether an idle re-learn had been performed. I advised a re-learn was done via gas-pedal sequence. He said the re-learns are done on their CONSULT (scan tool), but said he wasn't certain if it can be done via gas-pedal sequence. I advised it can be done via pedal sequence and advised this is how it was done on my car.

I also asked him if there was a way to see (via VIN look-up) if any ECM or TCM updates have been done and/or are needed. He said there is no way to tell by VIN. He said they would need to connect the CONSULT to my car to check for any updates. If any of needed, they would do them. I asked what the cost is for this, he said it's one hour's labor or $128. So basically, I'm looking at $128 + tax to connect the CONSULT to my car and check and see if it needs any updates.

- The service manual indicates idle re-learn can be done both on the CONSULT and pedal-sequence.
- Service manual indicates idle speed (with NO load) should be 650 RPM +/- 50. So basically, idle should be between 600-700 RPM under the following conditions:
A/C off, Headlights off, Defogger off.

I cannot find any info in the service manual regarding an idle spec while in Drive (D). I don't think there is a spec for that.

Try the following and let me know the numbers:
1. Have engine at normal operating temp.
2. Engine running and in Park (P).
3. All accessories and headlights OFF. Keep foot off the brake pedal. Steering wheel straight.
4. Check RPM in Park (P), then in Drive (D), then Reverse (R). What are the numbers for each?
5. Put back into Park (P). Turn on A/C. Do the RPM's rise a little to around 650?
6. Perform step #4 again. What are the numbers? Any different vs. when A/C is off?

 

I scheduled an appt. this Sat with my Infiniti dealer to do an ECM re-flash, as well as check out any other possible ECM issues. Doing this will hopefully eliminate any possible ECM-related causes.

I tried the 6 steps as I outlined in my post above. Sometimes the RPM will raise slightly to 650 RPM to compensate for the add'l load when turning on the A/C. When this happens, the vibration goes away. At other times, when I turn on the A/C, the RPM will NOT raise and it stays at 500 and the vibration is still there--and--may seem to get slightly worse for a second or two before reverting back to the typical vibration issue. Also, at times it will seem as though the vibration isn't as noticeable when the A/C is off.

However, all roads lead back to the fact that the vibration occurs when the RPM is at 500... load or no load.

I'll report my findings after the dealer visit on Sat.

 

Sweet, keep us posted as I'm pretty sure many of us have this issue.

 

Created a video this morning as per your steps, and oddly enough the vehicle acted as it should.

So - I created another about 3 hours later, and the same thing. Today, the idle increased in drive when the AC compressor engaged keeping the idle closer to 650. This isn't always the case.

Hmm.

-Eric

First video:


Second video:

 

Hi Eric,
Thanks for supplying the videos. I get the same behavior as demonstrated in the videos. In fact, last night I was heading to the movies. On my way, I stopped at a drive-thru for a quick bite. A/C was off the whole time and idle in Drive (D) was 500. While I was waiting in the drive-thru (car stopped) I turned on the A/C, and the RPM's crept up to 650 and stayed there the entire time. As I moved through the drive-thru, the 650 stayed where it should. I left the drive-thru, and went to the parking lot of the theater to eat. When I came to the next stoplight, the idle was back down to 500 and I felt the vibration again. It's seems like the A/C compressor, ECM (or whatever) that controls the load when the A/C is on, is not working properly (consistently).

 

UPDATE:
Well, I had my appt. at the Infiniti dealer on Saturday (9-21-19). I explained my concern again in detail, and advised I had already cleaned the TB’s, cleaned the MAF’s and replaced both air filters with OEM. Advised them too, I had done an idle re-learn via pedal sequence after cleaning the TB’s. My car has no mods (100% stock).

The adviser could feel the vibration in Drive (D), so I’m glad they were able to concur with what I was talking about. After about 30-40 minutes, the adviser reported that one of the TB’s was sticking a little. However, this was not due to being dirty, but rather in its operation. I guess “glitchy” would be a better word. They also reported the RPM’s were a little high on initial start-up (when car is warm). They also checked the engine and tranny mounts, but all was good there. The technician did a re-flash of the ECM, as well as an idle-relearn (on the CONSULT). Idle in P with all accessories off was 650; per specs. The adviser brought the car back to the service drive for me to check. I started the car and the RPM was at 650 in all gear (with A/C on or off). I said everything appears to be good at this time. They washed and vacuumed and I was on my way. Cost of the appt. was $128 + tax.

I had some errands to run afterwards, so I was driving (as normal) in stop & go traffic. Sure enough, at the first stoplight, the RPM’s went to 500. I thought, “Damn, here we go again!” However, this time I noticed the vibration was greatly reduced (A/C was on at the time). Another thing I noticed too was that the RPM in general seemed smoother. Even though I reported the RPM was smooth before the appt., I would say that the added smoothness I am noticing may be due to the reduced vibration and/or the possibility of the (now corrected) sticky TB? Who knows.

Anyway, as of this writing (9-24-19), I’d say the vibration is reduced by roughly 50-70%. I say that because it is not totally gone (i.e when in Neutral at 650). But, it seems to be reduced to the point that it doesn’t draw my attention as much while at a stop. In any event, I’ll gonna keep an eye on this and see how it goes over the coming weeks. I’ll keep you guys posted if anything reverts back to the way it was before.

If any of you guys go to the dealer to have this addressed (i.e. re-flash, re-learn, etc…) please post your results.

 

Thanks for the update!

What I'm taking from this is the idle drop is somewhat normal, and the vibration was reduced with an idle re-learn and flash?

Doe the G not have adaptive engine mounts? My Accord had active engine mounts that were designed to minimize vibration - maybe the lack of something similar on our cars is why we can feel vibrations?

-Eric