I need your help, G35driver members...

First, here are my mods:
Berk HFC, Invidia CBE, R2C Intake, UpRev Tune, Lightweight Pulley
2007 G35S A/T with 115k miles.

Here is what's happening:
The RPMs start to just keep revving past 3500rpm until I let go of the gas, and then the car jerks when I hit the gas again and it catches the next gear. This does NOT happen every single time, but more than 50% of the time while I'm driving. Also, if I drive aggressively it barely ever happens, and the shifts seem normal. But, when it does happen, it happens on cold start as well as once its been warmed up. Notice it happening more often when I'm going slower and not "flooring" the gas pedal. It sort of feels like its a transmission slip but the symptoms do not match up to transmission issue?!?! Very confused...

This is what I have checked so far:
-Trans fluid level is normal. Was changed during 90k service. Does not smell burnt.
-Motor oil level is normal, just changed within 1k miles..
-HFC do not seem to be clogged, as I have equal back pressure coming from both exhaust.
-the MAF connections are good, and air filter is somewhat dirty but nothing that would obstruct air.
-NO CEL LIGHT APPEARS on dash
-Have switched my car from 93 tune to 91 tune to stock tune... happens in all three.

ANY IDEAS?
- Could it be rear differential issue?
- Is it related to Transmission possibly?
- Could it be O2 sensor on HFC bc I basically scrape my cats on the pavement everyday bc car is so low. (but there is no CEL light ever).

Thank you very much in advance for your responses!

 

Perhaps the Crank Sensor, 02 sensor or even a faulty MAF might be the culprit. That's where I would start if this happened to me. Perhaps plugs and or a faulty head, but these 2 would be far fetched.

 

If its MAF it would definitely affect acceleration... however, OP said when he floors the car it launches fine... so this ones a hard one...


OP, did u flush ur tranny or drain and fill before the 90k or was it ur first time?

 

I'd be thinking shift solenoids or torque converter, but that just based on my understanding of the OP's description of the symptoms.

 

Trans fluid was drain and filled, NOT flushed.

Will be checking O2 sensors next.

Also, I'll try to get a video of the tach via cell phone later tonight.

Thanks guys, will keep you updated!

REFUSE TO GET ROBBED AT THE STEALERSHIP!!

 

If its not the shift solenoids or torque convertor like VQ said... then it sounds like a crank sensor to me which was a common issue on 1st gen Gs and FX that i have as well had similar issues with working fine at times and then 'slipping' feeling at times with limited rpms but after a while the CEL did come on and i was able to read the code.

 

If it was a flush on a high mileage car I know it can screw stuff up potentially.. but def not a drain and fill....

Just outta curiosity, were u pushing the car hard at all? In thinking maybe overfilled or heated tranny?

 

^ i thought about it but he said it happens more in normal driving and not when driving hard from what i understood which makes it harder to diagnose

 

Ok, so the CEL finally came on when I took it for a spin last weekend (been in the driveway for last couple weeks not being driven). Here are the codes:

P0732
P0733
P0734

Seems like these codes are associated with A/T Incorrect Gear Ratios (2nd, 3rd, 4th gears).
I've googled these codes and it seems as if it could be the valve bodies/solenoid sensor OR the throttle position sensor (TPS). I will be looking into both of these tomorrow when I had my car to the shop to get diagnosed further.

Will let you all know, thanks again!

 

UPDATE: Dropped it off at a shop last night for further diagnosis. After checking all external trans parts as well as sensors/wiring... they cannot put their finger on anything malfunctioning outside of the transmission.

Seems to be an actual internal transmission issue. BUT WHAT COULD IT BE AHHH?!

 

U under warranty?

 

Nevermind....ur at 115k

 

115k, no sir.

 

After looking at everything other than shift solenoids and torque converter, I am thinking more and more that either of these may be the issue here. Deciding within the next day or two whether I should have them open up the transmission to begin diagnosing the internals.

 

This is a "smart" transmission. With the use of proper diag equipment (Consult III, et al), there are a series of rudimentary system tests and checks that can be performed far short of "having them open up the transmission". Hopefully, they can get a clue into where/what the problem is prior to any tear down expense.