2007 350Z Engine Hesitation Issue

[nervman]

Hello everyone, I recently bought an 07 350Z that runs quite well except for one problem. (lol, I'm sure if a nickel fell out of the sky each time someone said that on here..)

Anyhow, when starting my car up from a cold engine and driving a couple minutes to where it has just warmed up I get hesitation issues below 2500 RPM in any gear, and is also reproducible in neutral (6 speed manual). This hesitation only occurs on very light acceleration and once the car warms up fully it dampens out a lot to where its not noticeable. The most interesting way for me to reproduce it is to sit in neutral and slowly let the RPM climb and every time right on the money the needle will sort of stick and engine bog a bit precisely at 1750 RPM, every time before finally moving up again. )As time goes on from being fully warm the amount of bogging gets smaller and more dampened)

I'm certainly not a car tech, but I have read that most vehicles starting up from a cold engine will not take inputs from most of the sensors until the engine temp gets to a particular point when they will be factored in by the ECU. My car operates perfectly fine until it reaches this now fully warmed up spot where the hesitation/bucking will occur and will soon dampen out. So I am leaning towards this being a sensor issue. I ordered 1 MAF to use in testing. This car has 2 MAF sensors (2 intakes) so I'll test on either intake with the assumption that the odds of both MAF being bad are probably kinda slim.

I would really appreciate it in being sort of nudged in the right direction as I continue to test and analyze the problem. What I really would like to do is remove both MAF sensors and run the car without either for about 10-15 minutes to see if the problem does not occur. I would assume that'd be a near sure fire way to eliminate the MAF, but is this a safe move to make and would I need to put some duct tape/masking tape over the holes when the MAF sensors are removed? I also replaced the air filters with new ones although I knew it was very unlikely to help anything.

So here is what I have planned:

- Remove both MAF, sensors run the car without it.

- Remove spark plugs and carefully retorque them or new replacements with a good torque wrench

- Replace O2 sensors (can this even be an issue) ?

- Check vacuum hoses (They seem fine to me though)

Anything else I should do, or anything I said I'd do that I probably shouldn't bother doing?

I REALLY appreciate any help I can get, its been irking me for a couple weeks. Although its not a severe issue, I don't really like taking off like a bucking bronco for that short space of time where the engine is just warmed up.

[OldmanPurdy]

I found that newer eletronic throttles can sometimes be twitchy when cold, case in point my girlfriends 06 civic si just went into the dealer for an ecu update to fix the exact problem you just described. I doubt that any of the the things you listed would be the issue with such a new vechicle, I personally would have the dealer run over it with their scan tool.

[Q45tech]

Why you visit dealer every 90 days [oil change] so they can find problems and do updates they can charge Nissan Warranty to accomplish.

[nervman]

Indeed I have done that, believe me I'd rather get someone else to take care of the problem. However I've taken the car twice and they've been unable to find the problem, i.e. if the car doesn't throw a code they write it off as being fine. I mean, how can a person call themselves a professional when they can only rely on codes? Its more likely laziness on the part of the dealership's master tech.

I am trying to fix the problem myself in the meanwhile and if I can't do it with some simple fixes I'll go back and demand better service or go to another dealership.

Anyhow I removed both MAF sensor wires and my car was running rich (based on the ample gas fumes I then smelled) and the issue wouldn't occur. But please just answer me this: By disconnecting the MAF sensors, what else would the ECU remove from the equation in terms of sensors? Will it still use the O2 sensor etc.? I would assume it'd still use the TPS...

Once I have the new MAF in hand I'll be able to test things more accurately, but the fact that I removed both MAF tonight and the car didn't give the same weird bogging issue at 1750 RPM I don't know if I can safely assume MAF or not, it was throwing an SES which might cause the ECU to change how it controls the car anyhow.

[mister2nr]

If you have taken the car in twice with the same problem just because the car does not have any codes and they can duplicate the issue, they still have the consult to go off of reading values. My suggestion is go to a new dealership. I don't know how many times I have repaired a car just by reading data monitor items without codes. But when you unplug the MAF your changing a lot in the ECU so its hard to go off of saying thats the issue at hand. Would not doubt your in the right track but I suggest a different dealer.

[driftingmy240sx]

try relearning your throttle ans pp values. turn key on for 3 seconds then turn off for 10 seconds, repeat 3 times then start the car. see if this has any effect on the symptom. while you cycle the key to reset the elec throttle and app make sure your foot is off the gas pedel.

[nervman]

I'll give it a whirl but frankly I would think throttle relearning would be a plausible fix if my car had this issue at any time regardless of time driven and temp.

I am theorizing that once the engine is warmed up to a certain point perhaps the sensors are first used but for some reason one of them doesn't yet give reliable readings or maybe I have a bad plug, maybe misfiring. I don't hear backfiring, but maybe the engine in this situation is just running lean.

I'll end up taking it to a dealership I'm sure but it sure helps if I could be armed with some info to maybe help guide them to things to look at. Its just a difficult situation as it can't be reproduced at any time, just in a small space of time just after engine warmup.

I still appreciate any further thoughts and those mentioned already. Thanks.

[mister2nr]

Well its always possible that a coil is going bad. I saw the other day a Murano with some miles on it though have a slight misfire only at certain times and found a coil arcing. But there are so many different things that can cause a misfire.

[nervman]

By the way, where exactly can I locate the ECM to I can plug in my ODBC II scanner. I was initially looking at the far right side on the passenger side underneath the glovebox and I saw what might be the ECM unit with two connectors already plugged in. Do I remove one of those or is the connector supposed to be already unused? Or maybe I was looking at the wrong spot... Thanks.

[mister2nr]

If you want to plug a scanner up you use the OBD2 port underneath the steering column. You don't plug it directly into the ECM. If you either feel around for it or crawl on your back you'll see a white connector to hook up to. But if you unplug the ECM you wont get any codes out of it.

[nervman]

thanks for the help mister2nr I really appreciate it.

Well I took it to the dealership and demonstrated the issue to the master tech, (I think I scared the living daylights out of him when he told me to also do a WOT). Anyhow the way it works with a situation like this is that they will consult directly with Nissan to let them make the call on what should be done because if Nissan is wrong about a potential fix that is applied the cost is theirs to bear, if the dealership makes a call and is wrong then they bear the cost and they will not do that. Long story short Nissan recommended putting in 5w30 oil because perhaps the oil in there was not 5w30 and it might've been the typical 10w30 most lube shops put in. So I drove the car and so far no bucking issues, so weird. I live in florida and this time of year cold weather is virtually nonexistent so its kind of hard seeing if 5w30 vs 10w30 really should matter but perhaps it does. Only after a week of driving if it doesn't occur I'll consider it fixed.

So strange though of all the bucking hesitation potential fixes out there (and there are many) changing the oil might be the answer. But then again these high compression high rev engines are supposedly designed under tight tolerances so who knows.

[mister2nr]

no problem. I understand the dealership with saying they want to talk to Nissan first; since I work at one I've run into those mind boggling issues. Keep us updated on the situation though if the problem occurs still or go's away for good.