Good evening G35 Driver.

Main issue:

RPM's bouncing low then back up at 0-30mph. Mainly when letting off the gas (video attached).

Troubleshooting done:

Transmission fluid check/drain & fill.
Air filter
Vacuum smoke test
MAF Sensor (replacement)
Throttle Body ( replacement)
3 peddle dance programming (multiple times)

Kind of out of idea's at this point. Starting to think it's the tranny.

 

Your rpm's are supposed to drop down to near-idle when you let off the gas going that slow. I don't see anything wrong in that video.

Which "pedal dance reprogramming" did you do, there's 5 different recalibrations for various systems that all use a pedal dance.

 

Good evening cleric670,

Appreciate the response, I've read plenty of your posts/responses and you've pulled me out of a few jams. Honor to virtually meet you!

I guess I can be a little more specific on the issue. On my video, if you focus on :37 seconds in you can see me let go of the gas. The rpm's drop then jump back up. On every other car i've driven the RPM's slowly go down to the relative speed. (Mom's camry, Uncles Tacoma, Aunt's Honda). I've been told this is REV matching but i'm confused why the RPM's would go so low? Almost to Idle then jump back up. This has been going on for almost a year and its only in stop and go traffic. There is also a slight jerk when this happens. Not sure if that can help with diagnosing this.

I've done the following (3) Relearn procedures about 5 times in the following order with a ECU reset beforehand.

Accelerator Pedal Release Position
Throttle Valve Closed Position
Idle Air Volume Learning (Throttle Position Learning)

I can obtain some more video footage to help identify the problem more clearly.

 

Ok yep I see exactly what you mean now, firstly are you 100% sure you did the idle air recalibration correctly? The engine AND TRANSMISSION were warmed up, steering wheel pointed perfectly straight (yes it has to be straight, steering angle sensor needs to be zeroed out so actually DRIVE THE CAR and stop in a straight line), and every single power consumer in the car is turned OFF including not touching the brake pedal, and the parking brake needs to be set.

The idle air recal will look like it worked regardless of whether it actually did or not, by far the easiest way to do that recalibration is with a bluetooth OBD2 scanner like the BAFX one on Amazon (highly recommend this unit, I keep one in every vehicle they're about $25) and use the Android app Nissan Datascan 2 (not the full PC version, the android app version). It has the protocol to verify the readiness state of the car then you just click a single button for the idle air recalibration.

I know for fact the idle air recalibration can cause issues like that but it's also usually pretty persistent idle issues in all situations, if the idle seems normal then focus on finding a vacuum leak, it too will cause issues EXACTLY like that. Vacuum leaks will also cause a sort of "delay or lag" when you stop the accelerator wide open, if you do have a little hesitation in engine rpm when you press the gas WOT when driving then it's almost definitely a vacuum leak.

The most common culprit on these cars is leaks along the PCV system, my rule of thumb is if you can turn/rotate the hose (wherever it's attached to a nipple) with your hands then it's too loose and leaking. There is 1 point on the PCV system that doesn't even come with a factory clamp, 3 vacuum lines total, one runs from the intake pipe to the left side valve cover below the throttle body, one connects the two valve covers together at the front of the engine below the intake plenum, one runs from the right side valve cover/pcv valve to the front of the intake plenum.

Add clamps as needed to keep those hoses from turning, if the rubber is cracked then just replace them all with a silicone hose kit, Z1 Motorsports makes a great hose kit for the PCV system.

Also check the intake tube for cracks and make sure the clamps are tight at the MAF and the throttle body.

The other vacuum line that could leak (not normally a problem but check it anyways) are the two hoses for the brake booster, one is directly from the brake booster to a hard metal line on the left side of the engine, one is from the intake plenum to the BATTERY BOX. There's a hard metal line that runs from the battery box behind the cowl over to the brake booster.

My gut is telling me it's a vacuum leak.

 

Do you have the A/C or defrost on??
My RPM's tend to hang a little higher whenever I have them on.

 

I literally am having the same exact issue right now. My idle is rock solid but rpm's bounce at low speeds, identical to your video. I cleaned my TB, MAF, and intake and also did the pedal dance resets. My idle is rock solid after those resets but still get the bouncing.

I found a hole/crack in my intake coupler so I replaced them both yesterday. I was hoping that the leak was causing the issue but the rpms still bounced a little with the new couplers. Maybe I'd have to do the pedal dances again after the replacement to fix it? Not sure, I'm totally stumped with this issue as well. Not sure if a hole in the couplers is a vacuum leak or if it would require an idle air reset to fix the rpms jumping. Figured the computer would adjust and it would suddenly stop bouncing if the couplers were the cause.

 

Yes you do have to perform the idle air recalibration again after you plug a vacuum leak.

 

Merry Christmas cleric670!

When I said you saved me in the past a few times I wasn't joking! I actually have the BAFX android OBD2 hooked up to my Amazon fire 6 tablet that stays in my car constantly. I've got torque pro running with the dash mode.

So I went ahead and bought the Nissan Datascan 2 for my tablet and successfully did the idle air recalibration. Unfortunately, that didn't fix the issue.

Furthermore, I have the full Z1 hose kit in red sitting in my trunk for emergencies. I'm the kinda guy who's don't fix it if it is not broken, but also like being prepared.

I'm going to replace the vacuum lines this weekend and see if that changes anything. Will report back with results.

Thank you sir!

 

Check your intake couplers, those can crack/break over time.
My current G35 does something similar, but not nearly as pronounced as that. I think mine is mainly the transmission downshifting when coming to stop or slowing down. Its only when the engine is still warming up to temperature (<170* F)
When I was new to G35's (and before I knew of the idle relearn procedure and sensitivity of the throttle body for these cars), I cleaned the throttle body on my G, only to have the erratic high idle and P0507. The car was doing very pronounced 'blips' with the idle when coming to a stop like yours is. On top of that, being that that particular car had over 240k on it at the time, the intake boots were cracked significantly. I did the idle relearn and later replaced the intake boots (thanks Z1) and I don't recall ever having another issue.

 

Good Afternoon cleric670,

Thank you again for helping me with this.

I went ahead and replaced all the hoses you mentioned in your previous comment.

(3) Vacuum lines.

1) intake pipe to the left side valve cover hose
2) connecting valve cover hose
3) right side valve cover to the front intake plenum

(2) Brake booster lines.

1) intake to the battery box
2) brake booster to the hard metal line.

I went ahead and used some stainless steel worm clamps made for hoses and made sure they passed the hand test you mentioned. Furthermore did the idle air recalibration after replacing the lines.

Unfortunately no dice. Still have the bounce in RPMs when letting off the gas. I did notice something after taking the 2nd drive a few moments ago. It seems as if the bouncing only happens when the transmission is warmed up. The first mile or so during cold driving the RPM's act as they should. I'm starting to believe it may be a transmission issue.

Let me know if you have any more thoughts. The Z1 hoses look good, the old ones were stiff as bricks.

 

Hey cleric670,

Any chance bad plugs or coil packs could cause this sort of behavior? Maybe a slight misfire that's not shooting a CEL code?

Just a thought.

 

I just double-checked all the connections at the intake. It looks like things are slowly starting to crack. I went ahead and ordered the replacements from Z1.

I'll see if that helps any.

 

I replaced my cracked couplers and did the pedal resets and still have the rpm issue. My gut says it would be a vacuum or throttle body related problem but theserb replaced his TB and all vacuum lines with no fix. I’ve found a few other G/Z owners online with the same problem as us but they’ve all given up on it. It’s rare and can’t find a fix, does anyone have more ideas?

Basically, rpms are dropping then bouncing back up under 40 mph. When it’s a higher speed above like 30 mph it drops to like 750 rpms (idle area) and rises again like at 0:35 in the video. But at lower speeds it’ll bounce down a few hundred then quickly bounce up like around 1:36 in the video. The bounces are different depending on the speed but once I hit 40ish it doesn’t do it anymore. Highways speeds are normal when I let off the gas. The quick rpm change makes it feels like a downshift does in tiptronic mode but the car isn’t actually downshifting. I’m pretty stuck here, out of ideas as well. Any suggestions are appreciated, odd to me that the speed changes the type of rpm drop.

 

When you're driving at about 20mph and you stomp the throttle to the floor wide open does it bog and hesitate for a second before the engine revs? If so it's a vacuum leak, might have to smoke test the intake to find it.

 

I haven’t had any bogging/delay when going WOT I don’t think. I’ll test it tomorrow going about 20 mph but on the highway my rpms react to the throttle normally.

Since theserb replaced all vacuum lines I feel like it won’t be a vacuum leak. I’ll definitely check though, can I do it with tb or carb cleaner and spray around a cold engine and look for rpm fluctuation? Not exactly sure how to look but I want to give it a shot to rule out a vacuum leak for sure. Rpms are rock solid at idle by the way. Thanks