240hoke Posted March 22, 2009 Share Posted March 22, 2009 Hey Guys, I have recently been trying to figure out a problem with the vq and it is about to drive me up the wall. Ill try and be as through as I can describing what is happening. Background: The car ran great when I first completed the swap for about 200 miles. It could be a coincidence, but this all started when I tried to start the car when the battery voltage was low and it went into throttle body fail safe. Once I got the codes cleared and charged the battery the car started and ran great however when I took it for a drive it would die when I came to a stop... When It happens and what it does: - The car starts up and idles smooth when cold with a idle of a little over 1,000 rpm. - If I let the car warm up in the driveway it 50% or the time after it warms up it will all of a sudden start to sputter and after coughing a few times and trying to save itself it stalls out. - Once its warm if I rev it up over 3K or so and then take my foot off completely it will drop past 600 rpm and stall out. If I pat the throttle a bit right before it dies it will recover and idle great (about 800rpm). - If I take the car for a drive it runs and drives great, however when I come to a stop or coast with the clutch in it stalls. -Whenever I restart the car 80% of the time it starts up and idles fine, the other times it coughs and sputters unless I give it throttle. - Every once in a while Ill take the car for a drive and it works PERFECT no hint of the problem at all What I have done: - Replaced the battery - Ran an ODBII code check. Nothing shows up pertinent to the issue. It throws plenty of codes but all related to things that I have unhooked, such as the a/c and power steering, chassis CAN line etc. - Tried to preform "idle air relearn" manually by pedal input several times. Cant confirm if it worked due to no check engine light. -Tried adjusting the fuel pressure: It was originally at 41psi which I changed to the factory 51 psi. Car ran really rich and problem was not affected so I lowered the fuel pressure to around 37. I have modified the fuel rails for a return system so my buddy recommended that I needed to only run 35-40. No change in problem. - Replaced the MAF with a good known working unit from my personal 350z. Didn't make any difference. - Watched fuel pressure when the car stalls as it is sitting in my driveway. It stays ROCK SOLID. - The TB , MAF, Intake, engine inside of the intake tract is clean as a whistle...motor has 500 or 600 miles on it total. Thing I am going to try: - Swap out the throttle body for a known good unit - Prefer Idle air Relearn using a Nissan Consult I am kinda frustrated with the issue out of my expertise with new motors. I have talked with a reputable 350z shop that has experience with modified vq's and ems, and they had never had the issue or any advice. I was told they had no issues with a factory setup unless it threw a code. I have also talked with my buddy who is a nissan master tech about the issue as well and he has no advice to offer either. Really hoping somebody here can help!!! Quote Link to comment Share on other sites More sharing options...
DRZ man Posted March 22, 2009 Share Posted March 22, 2009 I had a 350z last week with the same problems but not codes, with consult check voltage operation to the tb and it was out of specs, replaced the tb, car runs great, with no problems. Quote Link to comment Share on other sites More sharing options...
240hoke Posted March 22, 2009 Author Share Posted March 22, 2009 Werd thats the kind of stuff I want to hear!! Thanks for the tip, Ill be trying that next time I am home. Quote Link to comment Share on other sites More sharing options...
Canadianz Posted March 22, 2009 Share Posted March 22, 2009 Check your Idle air valve, if its anything like those on the RB's it can cause a very similar problem, so software wise it might be 100% and is learning correctly but could be malfunctioning. My RB without an idle air unit acts exactly like what you are describing. If it comes off easily it might be an easy check. Also like the other fellow mentioned check your TB.. try to put a stronger return spring on yours, it might not be closing all the way or might be sticking part of the time. You've probably thought of this stuff already though its worth a shot before you swap the whole TB. Chris Quote Link to comment Share on other sites More sharing options...
DRZ man Posted March 22, 2009 Share Posted March 22, 2009 ^^^ thats integrated in the tb. the idle valve you talking about. Quote Link to comment Share on other sites More sharing options...
240hoke Posted March 23, 2009 Author Share Posted March 23, 2009 Yea as far as I understand the ECU modulates the throttle plate acting like a air bypass valve? Quote Link to comment Share on other sites More sharing options...
irax Posted March 23, 2009 Share Posted March 23, 2009 yeah check your voltages to the ecu the tb the gas pedal Quote Link to comment Share on other sites More sharing options...
Jared Posted March 26, 2009 Share Posted March 26, 2009 Performed the IAVL with a Consult2 before replacing anything. Good possibility that got messed with during the low voltage condition. The IAVL normally takes care of these things. Quote Link to comment Share on other sites More sharing options...
DRZ man Posted March 26, 2009 Share Posted March 26, 2009 Performed the IAVL with a Consult2 before replacing anything. Good possibility that got messed with during the low voltage condition. The IAVL normally takes care of these things. Agree 100% with this post. Quote Link to comment Share on other sites More sharing options...
Pharaohabq Posted April 23, 2009 Share Posted April 23, 2009 Any Luck, Austin? Quote Link to comment Share on other sites More sharing options...
junglist Posted April 24, 2009 Share Posted April 24, 2009 I had the problem with my 350Z...but it was my MAF and you said you already replaced that. You are lucky that you have a testbed in your daily Z to verify parts are working properly. Quote Link to comment Share on other sites More sharing options...
240hoke Posted April 26, 2009 Author Share Posted April 26, 2009 No progress thus far. I havent been back home to work on the car since I originally posted. The semester is finally almost over and Ill be able to get back to it in a week and a half. Ill update when I figure it out. Quote Link to comment Share on other sites More sharing options...
benitoz Posted May 3, 2009 Share Posted May 3, 2009 I had this problem on my 05 350z that I had putt twin turbo kit on. I remember everything was cool other then it would stall going up to lights ect. Basically exactly how you describe. I understand the reason as the turbo's caused more restriction for the afr to get a good reading at idle, or when running low rpms. The guy at the 350z shop (forged performance) said at the time the 03 04 ecu's nissan can adjust the idle. but not 05's so I had to keep my ac on. The guys told me to do this untill my tuner tricked the ecu with a tuning program. Many people were having specific problems just like yours. If the idle dips down to far it loses signal and pow it dies. if you were in a stock 350z id say turn on ac and see if it dies. maybe the position of your afr is causing a goofy reading. if there was some way to make the ecu think you had accessories on, like Ac ect. it for some reason will not let the car die at idle. I tested it vigorously. Eventually the tuner found a way on the u-tec raise idle. But I had to live with this for a bit. Good luck this may be of no help but it really hit home the way you described whats going on. Quote Link to comment Share on other sites More sharing options...
240hoke Posted June 8, 2009 Author Share Posted June 8, 2009 I wanted to update this thread as I figure it out and it was an easy fix. The problem WAS the idle are volume. However relearning the idle air volume was not possible using the consult due to the amount of codes thrown by the ecu....all the chassis codes, a/c, power steering, etc, etc. Anyway the fix was simple. Disconnected the battery cables, stuck them together for a minute or so discharging all the power from the ECU and viola the engine ran great. It has continued to run well and idle ever since Quote Link to comment Share on other sites More sharing options...
Pharaohabq Posted June 8, 2009 Share Posted June 8, 2009 I was going to post something on this... Apparently the 350Z's also have/had an issure where if you're revving high, say on the highway, then shift to neutral and coast, it can cause stalling since the computer doesn't understand the speed difference as compared to engine idle. They said to fix it you do just what you did, disconnect battery. turn on headlights to drain... glad you fixed it. I hope my CEL's won't be too bad. The techs here have hardly played with their consult3 at all. Phar Quote Link to comment Share on other sites More sharing options...
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