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 short shifter, 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 flow cats, 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 condition 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 flush 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. I tried 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

Yeah, that seems quite the issue. I do a lot of highway driving more than beating on mine (had a blast on the Dragon the other week) and I've never had a single issue with hesitation...When you have the issue does it seem to be the motor stumbling and causing the hesitation or does it seem to be the motor is reacting from drag from the transmission or rear gears? Stumbling via the motor would be more of a misfire feel than the motor losing RPM due to what could be described as accelerating while dragging the brakes.

The loss of power sounds like ignition retard. Will the Accessport allow you to log ignition timing for long enough to capture the ignition timing when the issue occurs?

As for the transmission, I know this sounds crazy, but go back to whatever Nissan used for the transmission lubricant. I have not had good luck with synthetic gear oil in my transmission for the same problems you're describing. My theory is that the synthetic oil is so slippery, the synchros don't work as they should, and so it's hard to get it into gear because the synchros have trouble getting the gears lined up to each other.

Let us know about the redline. I use it as well. I used to blend mt 90 to get a mt85 mix which is what our car wants, but now redline makes it. Look it up. Get the mt -85. Its what i used from when the car came off the lot and no problems.

i know there was a throttle control issue with these cars (i used to own a 2010 g37s coupe 6mt). it required a flash with some upgraded program.

i would start with every possible area, and work my way back:
1. intake system: MAF (air intake temp sensor if separate from MAF), throttle body(clean, replace), and since the PCV system is related to the intake manifold, i'd start cleaning and replacing valves, hoses, etc.

2. exhaust system: check the temps of the cats. make sure they are not getting too hot. that could be the result of clogged cats, thus robbing you of power. place them if they are running too hot.

3. fuel delivery: start with the fuel pump, fuel filter(if equipped), injectors(replace the or send them out for ultra-sonic cleaning).

4. brakes: check for sticky calipers. go for a safe but 'spirited' run. check the temps of all the calipers. maybe one is sticking?

Thank you everyone for the replies!

Fezzik wrote:Let us know about the redline. I use it as well. I used to blend mt 90 to get a mt85 mix which is what our car wants, but now redline makes it. Look it up. Get the mt -85. Its what i used from when the car came off the lot and no problems.

I did the MT flush yesterday. At first I opened the filler plug and the fluid that was in there came out in a solid stream, so the shop had overfilled the MT. I let that drain off completely, closed it up, and drove the car around. The notchiness did get slightly reduced, but it was still hard to get into gears at a completely stop. I flushed the fluid out completely and put in 2qts Redline MT90 and roughly 1.1qt MTL, and I made to let it drain off completely so that it wasn't overfilled. The notchiness shifting through gears while moving did go down a bit, but it is still hard to put the car in gears while at a stop.

5.56 wrote:i know there was a throttle control issue with these cars (i used to own a 2010 g37s coupe 6mt). it required a flash with some upgraded program.
i would start with every possible area, and work my way back:
1. intake system: MAF (air intake temp sensor if separate from MAF), throttle body(clean, replace), and since the PCV system is related to the intake manifold, i'd start cleaning and replacing valves, hoses, etc.
2. exhaust system: check the temps of the cats. make sure they are not getting too hot. that could be the result of clogged cats, thus robbing you of power. place them if they are running too hot.
3. fuel delivery: start with the fuel pump, fuel filter(if equipped), injectors(replace the or send them out for ultra-sonic cleaning).
4. brakes: check for sticky calipers. go for a safe but 'spirited' run. check the temps of all the calipers. maybe one is sticking?

To do the flash/program upgrade, did you just have the dealership do that?
As for your suggestions: 1. I've cleaned everything, MAF, intake filters, throttle bodies, intake piping, and ran Seafoam through the intake manifold via the brake booster line. After all that I used the "without CONSULT" procedure in the FSM to do the Idle Air Volume Relearn. the car settled back into the 650rpm idle that it should be. Doing all that has no affect on the situation. I have heard the throttle bodies on this car are rubbish, but I haven't had much luck with testing them to verify proper operation (been thinking about just replacing them). I need to go further and check the PCV valves and hoses (a project for when I have enough time).
2. Using an infared temp gun I checked the temps of the cats and the piping before and after. Fully heated up the cats were around 300F, piping before was around 500F, piping around was around 250F. Not sure if those are good numbers though...
3. I had a shop conduct a fuel injector cleaning, but all they did was connect a pressurized can of cleaner to the PCV valve and force that through the fuel rails and injectors. This had no affect, so i don't even know if it mattered. Another side project I want to do is to go and pull the injectors and inspect/clean or replace. The fuel filter is embedded in the fuel pump and does not require replacement unless the pump goes. I need to troubleshoot this still.
4. Brakes are not the issue. I have the Racing Brake upgraded kit for the Sport brakes and I installed myself. I check the rotors frequently for warp and already checked calipers for proper operation, so that has been ruled out.

float_6969 wrote:The loss of power sounds like ignition retard. Will the Accessport allow you to log ignition timing for long enough to capture the ignition timing when the issue occurs?
As for the transmission, I know this sounds crazy, but go back to whatever Nissan used for the transmission lubricant. I have not had good luck with synthetic gear oil in my transmission for the same problems you're describing. My theory is that the synthetic oil is so slippery, the synchros don't work as they should, and so it's hard to get it into gear because the synchros have trouble getting the gears lined up to each other.

I'm going to check the shifter assembly to make sure everything is the way its supposed to be. If that doesn't change anything then I'm going to go back to the Nissan fluid for the MT. As for the Cobb, it had a reading for timing, but that stuff is still too advanced for my level, so I didn't know what I was looking at. At this point I got rid of the Cobb because it corrupted my stock ECU. I have been thinking for a while now that either my timing is screwed up and the ECU has been retarded the timing, or I have an issue with the VVEL. For something like that I want to find a good local tuner to check this out for me, but I haven't found a good one yet.

audtatious wrote:Yeah, that seems quite the issue. I do a lot of highway driving more than beating on mine (had a blast on the Dragon the other week) and I've never had a single issue with hesitation...When you have the issue does it seem to be the motor stumbling and causing the hesitation or does it seem to be the motor is reacting from drag from the transmission or rear gears? Stumbling via the motor would be more of a misfire feel than the motor losing RPM due to what could be described as accelerating while dragging the brakes.

From what I can tell I don't think it is a misfire. This may sound weird, but when I accelerate from a dead stop and this sluggishiness occurs I swear I feel the sensation of fluid gurgling through the shifter and the accelerator pedal. This could just be in my head, but then I also notice a faint sound of gurgling fluid. The sluggish feeling definitely feels like something is pulling against the engine, causing the engine to drag. Once I hit about 15mph the acceleration feels normal. However, sometimes when going at speed on the highway and i downshift and hammer it to speed up quickly it feels lacking in acceleration (again this could just be my imagination). I thought that maybe the clutch was sitll partially engaged or that it was an issue with 1st gear since I knew the snychro was going (this was before I had the transmission replaced). So I did pulls from 2nd and 3rd, but I experienced the problem in these gears as well (I was able to identify the problem separate from the slower acceleration that occurs because of trying to pull from a higher gear). Sometimes I wonder too if my LSD is causing the problem. I have been running Motul Gear 300 75W90 synthetic oil in there since 30K miles, but this problem did not start until around 50-60k miles. Also, I always turn VDC off as soon as I get in the car, and I don't see the SLIP light come on when the sluggishiness occurs, and I've done some crazy driving to test the functionality of the LSD and it seems to be working properly.

At this point, based on the research I've done, talking with others, and things I've done to rule out other possible causes, I'm thinking that my VVEL might be acting up and causing ignition retardation. But this is just a theory and I need to find a "good" tuner out here that can look into this for me. In the meantime I'm hoping to get some insight from the forums.\

Thank you for replying, I really appreciate any help I can get!

Injectors need to be cleaned via ultra sonic cleaner machines. Not some can of crap