Hey everyone, first off sorry, but this will be a lengthy post to ensure I cover all the details (I even had to reply to my post to include everything!). I also included details of another ongoing problem I’m having as I think it may be connected. I did extensive research online to no avail, and so I finally decided to write this post

Car details 2008 G37S Coupe 6MT

Mods include Eibach Pro Springs, Hotchkis sway bars, ADVAN RS-D 20x9 F 20x10 R wheels, Racing Brake 2-piece brake rotors and ET500 street pads, Stillen Lightweight Crankshaft Pulley, K&N drop-in filters, TWM shortshifter, Z1 Motorsports lightweight clutch and flywheel kit, ZSpeed heavy duty CSC (Wilwood), and 370Z OEM clutch master cylinder

Mods removed Stillen ceramic headers, Fast Intentions high flowcats, HKS Hi-Power catback exhaust, Fujita short ram intakes, and COBB Accessport ECU tuner

Car currently has 78k miles on it and spent entire life in San Diego

Always put 91 octane from Shell or Chevron, and used Seafoam in gas tank every other month

I bought the car 2nd hand in June 2011, previous owner bought car brand new in Oct 2007 and put 25k miles on it before I bought. Car was in mint condition and ran great

Maintenance history At 30k miles I flushed the LSD with Motul Gear 300 75W90 synthetic oil, flushed MT with AMSOIL GL-4 75W90 synthetic oil, flushed coolant with Prestone 50/50 pre-mix, changed serpentine belt with Gator racing belt, flushed clutch completely and added RBF600, cleaned air filters using K&N refresh kit, cleaned MAFs, intakes, and throttle bodies with appropriate cleaners, ran Seafoam through intake manifold via brake booster line, checked spark plugs for ccondition and gap (all okay), and replaced cabin air filter. At 60k miles conducted the exact same maintenance as 30k, but used Motul Gear 300LS 75W90 synthetic oil for LSD and MT. Every 15k miles I clean entire intake system and flushed clutch with RBF600. Every time I took apart the intakes to clean the components I would have the battery disconnected and when I put it all back together I would follow the learning procedures in the FSM (procedures for without CONSULT) and verify proper operations. I change the oil and filter every 3-4k miles using AMSOIL 5W30 synthetic and AMSOIL filer

Driving Habits I am not easy on this car by any means. I do very spirited runs in the mountains. I have also auto-crossed the G. It is my daily driver. Hard accelerations at stops, hard/fast turns, double-clutch downshifts to engine break during daily driving. Car is also a garage queen, both at home and work. From the beginning of having this car my habit of taking off from a dead stop has always been to blip the throttle to about 2500rpm, then begin applying pressure to accelerator and releasing clutch pedal simultaneously as the rpm dropped to around 2k rpm

The Problem I'm experiencing is that the car has sluggish acceleration from a dead stop until about 15mph and then its acceleration feels normal. This problem occurs randomly, but occurs more often when the car is hot and the sluggishness is noticeably worse when the car is hot. The problem first started about 1.5 years after owning the car and the problem just suddenly started occurring even though I had done nothing to the car at the time it started or a couple months before it started. The problem feels like something is holding the car back. Almost like the clutch is still partially engaged in 1st, or as if something is pulling against the engine to slow it down. About 6 months after this issue began I noticed that my average MPG dropped by 2, but my driving habits didn’t change. Also, I used the COBB AP to monitor parameters and the air fuel ratio remained at around 14.7 while idling, rpm staying steady at 650rpm idle, and STFT and LTFT did not change from before the issue began

Steps I've taken so far (everything listed here made no difference)When the problem first occurred I tried to reflash the ECU using the COBB AP. Itried a 24 hour battery reset. I tried cleaning the intake manifold, intakes, MAF, and throttle bodies. I tried flushing the clutch with RBF600 thinking that maybe the clutch was not fully disengaging. Around the time the issue began an engine code tripped that the EVAP system purge valve control valve (located at the top of the engine, near the firewall side) was receiving low voltage from the battery. I followed the steps in the FSM to test the power line, the communications line to the ECU, and test the valve and all readings were nominal. I put it back together and cleared the code and it hasn't come back since. I tried taking the car back to stock, reinstalled the full stock exhaust, stock intakes, and removed COBB (tried to remove COBB using COBB's reflash/remove software option). No change, but I did notice my intake air temps drop from around 160F to 100F, and my oil temp dropped roughly 10F to a high of around 220 (hot day and stop and go traffic). I took the car to a tuner with the latest CONSULT version and we found out the stock ECU was corrupted by the COBB, so I had that replaced and threw away the COBB AP. Doing some research someone with a similar problem was able to fix it with an injector cleaning, so I had the dealership do that (connecting a pressurized can of cleaner to inlet side of PCV valve going to fuel rails). I did a compression check on the cylinders, but all readings were good. I replaced the spark plugs, even though the ones installed were still good, and verified correct gap. (continued on first reply)

 

(Continuation of OP) While this acceleration problem has been occurring I have been dealing with clutch/transmission problems as well. Roughly 4 months after the accelerator problem began (1.5 years ago) I lost functionality of my clutch while driving. Had the G towed to a shop where they told me the rubber hose going from the MSC to the CSC of the clutch system had broken down internally (guessing that the hose broke down from heat from the exhaust/MT) and the pieces went up into the MSC and completely clogged it. The MSC and rubber hose were replaced, but the CSC was left as is because the shop said it was fine. About 1 year ago I had the Z1 Motorsports lightweight clutch and flywheel kit installed by a local specialty shop. I drove the car easy for the first 500 miles to break in the clutch and it felt great, also the acceleration problem seemed to have dropped off. However, towards the end of the break in period while I was still driving the car easy the acceleration problem returned and felt even worse than before (sometimes it was so bad it felt like the car was going to stall out completely). Also, shifting into gears started becoming very notchy and when the system was heated up and while the car was running and at a complete stop it was very difficult to shift from neutral to first or reverse (I would have to force the shifter into gears). Eventually (about 10 months after the clutch kit was installed) I lost functionality of my clutch again. Had the car towed to a local Nissan dealership (highly recommended to me by several car people) and we found out that the stock CSC cracked and started leaking. This was my fault for not finding out that the stock CSC is rubbish and can’t handle aftermarket clutches. At this time we also identified that my synchros for first, second, and reverse were starting to fail. At this time I had a new OEM MT installed, the 370Z OEM MSC, the Wilwood HD CSC, and we checked the condition of the clutch and flywheel (we noticed the clutch cover had 1 screw missing a washer and there were some isolated hotspots on the pressure plate, but no damage to any components and the clutch disc still looked new). The mechanic noticed that the clutch cover from the aftermarket kit was actually from the VQ35, but I confirmed with both Z1 Motorsports and ZSpeed that there wasn’t going to be an issue with the kit and the CSC (good to go). Just over a week ago I got the car back from the shop with new transmission, MSC, CSC, pilot bearing, fresh RBF600 in the clutch, and Motul Gear 300LS in the transmission. The car felt significantly faster accelerating through all RPM ranges and gears, but the shifter was extremely notchy and once the car was heated up, running, and sitting completely still it was extremely difficult to shift from neutral to first or reverse, and moderately difficult to shift from neutral to any other gear. The acceleration problem was not present at all for a week, but I was fighting with shifting into gear from a dead stop (while moving the car shifted to all gears notchy, but easily). I talked to the dealership mechanic and the mechanic from Z1 Motorsports. Based on those discussions I checked the adjustments of the limit switches and MSC shaft connecting to the clutch pedal (roughly 1 week after I got the car back). I noticed that there was slack in the MSC shaft when I moved the clutch pedal, but the Clevis Pin that connects the two had tension against it when the clutch pedal was fully released. I adjusted the limit switches and MSC shaft so that the Clevis Pin and MSC shaft had slack when the clutch pedal was fully released and adjusted the limit switches to be within spec of the FSM. The very next day as I drove the car to work the notchy and shifting problems were still present, and the acceleration problem returned in full force

Future Plans I'm going to flush the MT fluid with Redline MT 90 and MTL mix, and check the linkage from the shifter to the MT. As for acceleration problem, I'm stomped and seeking help here

 

To address your issue regarding ... extremely difficult to shift from neutral to first or reverse

Make sure your shifter guide plate has been properly adjusted. This should be done anytime the transmission is removed and reinstalled/replaced.

 

Thanks for the advice! Checking the assembly of the shifter, including the plate, is on my to-do list for this weekend when I take it apart to look at the linkage. The specialty shop that originally installed my Z1 Motorsports clutch/flywheel kit had not properly adjusted the plate, making so that the only way I could shift into 5th and 6th was if I pushed the shifter down like you have to do for reverse. I was so terrified to shift to 6th in fear of accidentally going into reverse lol!

 

[QUOTE=Snypos;3821648][FONT=Times New Roman][SIZE=3]
The Problem I'm experiencing is that the car has sluggish acceleration from a dead stop until about 15mph and then its acceleration feels normal. This problem occurs randomly, but occurs more often when the car is hot and the sluggishness is noticeably worse when the car is hot. The problem first started about 1.5 years after owning the car and the problem just suddenly started occurring even though I had done nothing to the car at the time it started or a couple months before it started. The problem feels like something is holding the car back. Almost like the clutch is still partially engaged in 1st, or as if something is pulling against the engine to slow it down. About 6 months after this issue began I noticed that my average MPG dropped by 2, but my driving habits didn’t change. Also, I used the COBB AP to monitor parameters and the air fuel ratio remained at around 14.7 while idling, rpm staying steady at 650rpm idle, and STFT and LTFT did not change from before the issue began

I had this problem on my bone stock G37S 6MT Sedan. I took it to the dealer for diagnosis, but they could not reproduce the problem. Once I get into this mode, it would happen at every time I started from a complete stop. The only way for me to get around this is to let the clutch slip more as I pressed the accelerator. Would love to hear if you found a solution to this problem

 

Yeah my shifting issue usually doesn't occur until the car is warmed up, but I have noticed it sometimes when the car was cold. Like you, once the problem starts it happens every time I come to a complete stop and put it in neutral. I have to practically jam the shifter into 1st or reverse. The rest of the gears are hard to get into as well, but 1st and reverse are the worst 2. When the car is acting like this I turn it off and shift through the gears. I actually notice some difficulty getting into gears with the car off as well. My workaround is to either put it into 1st or reverse when the car is still rolling at a very slow speed right before coming to a stop and then just holding down the clutch pedal until I can go again. Or, shift to 3rd as that is usually the easiest to get into and then shift to 1st or reverse.

I followed the FSM and a write up I found on Speciality Z for checking/adjusting the clutch pedal. The Celvis Pin that holds the MSC shaft to the pedal was taut/under pressure with the clutch pedal fully released. I was able to make adjustments so that it "floats" and moves freely while the pedal is fully released, and ensure there is still slack in the MSC shaft when pushing down the clutch pedal. I also made sure both limit switches were properly actuated. This didn't make a difference though, so that wasn't the issue. Just yesterday I flushed my MT with new fluid. The first thing I did was remove the filler plug of the MT and it pissed out MT fluid at enough of a rate to be a solid stream, so the shop had overfilled the MT fluid. I let that drain off until it stopped completely, closed it up and drove the car around. It did get slightly easier to get into gears, but still required a lot of force for 1st and reverse. I flushed the fluid out completely and put in 2 quarts of Redline MT90 and roughly 1.1 quart of Redline MTL (this makes for a mixture of 75W85 which is ideal for our car and in my temperature area). Sadly this also made no difference.

I had intended to take apart the center console to check the shifter assembly, but I ran out of time over the weekend, so I will need to do that next weekend.

 

Any update on this? Would love to know if you figured it out