I should add, the transmission control module (TCM) will change the shift logic to compensate for driver's with a lead foot, this typically only takes a day to make full correction.

Auto tranny only though.

 

My car had been driven by the dealer and he'd done a lot of work done on it. He told me after he'd got my money that he'd spent $3000 on it. Perhaps there were quite a few problems he rectified that the ECU thought were still present and was unnecessarily compensating for? I do know that the car had been bought from and 'sold back' to the dealer after 3 months, so there could well have been a major problem previously.

As far as the TCM is concerned, are you saying that it will actually reduce sensitivity to throttle input if I regularly accelerate hard?

 

The TCM does send data to the ECU but it's not used to modify the throttle like you're thinking, the TCM shift logic takes place entirely in the transmission via dampening the fluid pressure levels at the tranny throttle body. The difference in "feel" that you would notice is faster gear engagement, making it more "snappy" when it shifts rather than smoothly sliding from one gear to the next, the higher pressure levels just makes the gear transition faster.

My wife HATES it when I drive her car because of this

 

Unfortunately this problem has returned.

Immediately after the reset, the car was a lot more responsive and the steering tighter. It has gradually reverted back to its state prior to the reset. It's a 10 year old car, just shy of 100k, maintenance history unknown but owned by the same guy for 7 years of its life.

I don't have the technical skill to fix things myself, so I'm going to take it to a mechanic. Before I go though, does anyone have any suggestions as to what issues they might find or questions I should ask?

 

I strongly recommend you get your diagnostic done at the local Nissan dealership, a diagnostic fee is going to be about the same regardless of where you take it but the Nissan folks have the exact tools and computer to determine the problem with little guesswork (interpretation skills vary from one mechanic to the next obviously). If the Nissan dealership isn't an option then take it to a shop that SPECIALIZES in transmissions.

If it were my vehicle I'd start looking into electrical issues, it sounds like something is giving the ECU/TCM bad data to work with. The first point to start is the grounding/bonding system of the vehicle which is fairly notorious for corrosion. There are a bunch of ground wires bolted to various parts of the chassis and engine to electrically bond the entire system together. Battery negative terminal AND the other end of the wire where it bolts to the chassis next to the battery. Supplementary ground inside the battery compartment. Main engine to chassis bonding jumper (passenger side of the engine down to below the coolant reservior). Transmission ground located at the front of the engine on the top side of the timing chain cover. Engine main harness located right next to the transmission one on the timing cover.

Get your mechanic to use a wire brush to clean the lug, bolt, and mating surface and apply electrical anti-oxidation grease. All it takes is a little electrical resistance due to corrosion to throw the whole system out of spec, the ECU/TCM gets sent a lower electrical value than actual conditions so it doesn't make the right correction and the signal sent back is bad as well.

 

The nearest Nissan dealership is about 90 minutes from my house, so it would be possible on a weekend if they could do a same day repair.

Oh, that oil burning issue I mentioned a while back? I looked at the engine bay and underside of the car today to see if I could see any wiring that looked corroded (not that I know what to look for, but I was bored). I found burned oil close to where, according to Google, the valve cover gasket should be. Further googling suggested that a valve cover gasket leak could cause acceleration problems. Do you think that leak could be related to the poor throttle response?

 

Well here's a situation that happens, if you have a clogged PCV port inside the valve cover, or the PCV valve itself, then it builds pressure inside which eventually blows out the gasket. The PCV valve is cheap and easy to fix on this vehicle, unhook the tube, shake it to see if the ball is rattling around inside it, if not spray it out well with brake cleaner or some other solvent (or gasoline) until it's not sticking anymore, if it won't unclog then buy a new one for $10. A clogged port in the valve cover itself has been an issue on some motors, I personally have never had the problem but I think it could be diagnosed by hooking a vacuum pump up to the hose for the PCV valve and sucking vacuum to make sure air passes through the valve.

A messed up PCV system will DEFINITELY cause throttle issues.

The valve cover gasket is known to fail on it's own sometimes, unrelated to any PCV problems.

 

I took the car to the place that specialises in imported cars. It's the place recommended by the good local body shop. I wanted to get the oil leak looked at and I'm going to have to wait until school vacation in January (I'm a teacher) before going to the nearest Nissan dealership. I don't know of any place that specialises in transmissions in my small provincial Korean city.

I told the mechanic that a knowledgeable person on a G35 enthusiast website had suggested checking the electrical system. He didn't seem very interested and took the car on a very short test drive and claimed there was no problem. I insisted there was and took him on a drive to recreate the problem. He acknowledged it.

He cleaned the throttle body and tried to reset the ECU. His computer wouldn't work... something to do with voltage. He tried to reset 'manually', by which I think he meant the pedal dance or something similar, but had no luck. Right now the car has a fluctuating idle and is staying overnight in the shop. The guy has been working on it for hours and claims he couldn't get the timing right for the pedal dance. Sounds like they screwed something up. At least they're only going to charge $30, which is their basic fee.

As for the oil leak, they said it's not a big deal and not worth the cost of the repair.

It definitely sounds like I'm going to have to visit Nissan in January.

 

The pedal dance requires you to use a clock that displays seconds, it's actually really easy to do...

http://www.nicoclub.com/archives/g35-350z-ecu-reset-procedure.html

 

The mechanic said he's tried it "100 times" since cleaning the throttle bodies and he can't fix the fluctuating idle. It happens in Drive, not just Park, which makes the car difficult to manage at low speed. It feels like you're wrestling with it.

I got a note written in computer-translated English saying that the shop is sorry because they made a mistake while cleaning the "sensitive" throttle bodies and I need to take the car to the nearest Infiniti service centre.

Hopefully Infiniti will be able to send someone over here, as I don't want to take the car on an extended journey in this condition.

I hope they haven't damaged the engine too much already while repeatedly attempting the pedal dance. They clearly have no idea what the issue really is.

I'll probably be asking the local shop to cover the Infiiniti repairs if it's more than a couple hundred USD.

 

They probably broke the throttle actuator motor, if you try to work the butterfly by hand it strips the gear out on the motor. It'll be about $500-$600 at Infiniti to have them replace it.

It's possible they are just ignorant to the pedal dance which also needs to be properly completed anytime you unplug the throttle body.

 

Don't you need to go and get your ECU reflashed after cleaning your TBs?

As far as your experience, as soon as a mechanic says he sees no problem i would personally GTFO of there. A lot of mechanics will not touch any electrical or computer problems for the simple reason they have no clue about them or how to fix it.

 

ECU reflash, no

ECU reset, no but it is a good idea since you don't know wtf that "mechanic" was doing.

Idle air reset, yes since the butterfly in the throttle body was likely moved.

The car won't idle (or even run properly) until the computer knows exactly where everything is, things have been moved.

 

Had a very big hesitation (more of a complete engine shut-off) today after making a left turn and then hitting the throttle at about 30-40%.

It began to accelerate then lost all power for approx 0.5 secs before picking up again. Felt like total shutdown of ignition/fuel -- first time this has happened. Did not see the slip light flash or feel the car step out.

I parked and plugged in my wireless OBD2 scanner and went for a 30 min drive. There were no codes, timing advance, intake temps, vacuum, throttle position readings all seemed normal and the hesistation did not return.

Only odd thing I can see is that my battery voltage was steady at 14-14.1Volts (usually drops down to 12.9-ish after a few minutes) and it rained all day yesterday, although I drove in the rain, today no precip but it is cold out.

 

I'd remove/clean/inspect the primary battery cables, both ends of each cable. Clean them up with a brush, apply anti-oxidation grease and reinstall.