2005 G35x, 93k miles:

1) As of lately I'm noticing that after the car has been sitting overnight & I start it, the starter turns the engine fine but it's like as soon as the engine has been started, it stumbles for a quick second like it's about to die & then recovers. No abnormal signs after that. What things should I be checking? Anyone ever have this problem?

2) I notice I have a lot more visible exhaust then other cars. I could be sitting at a red light surrounded by cars and see minimal smoke from their tail pipes; I look in my rearview/side mirrors and I have clouds of exhaust smoke. This is even after a 30 minute drive where the fuel system should be in closed-loop. No codes.

3) How steady should the tach needle be at idle? Mine fluctuates a little bit...maybe +/- 50 rpm. Also if I'm driving and then coast, sometimes the tach needle falls normally but then bounces up 500rpm and then might do the same thing again...like it can't figure out where it wants to be when I coast.


My drive belts have a little squeal & I need to replace them but could they be causing any of these issues?

 

When is the last time you have done a full tune up on your car ie: spark plugs, throttle body/MAF sensor/ injector cleaning? Drive belts wouldn't cause the car to smoke.

 

Just got the car at about 91k miles. Only thing I've done is an oil change. Once I hit 100k I was planning on spark plugs & TB cleaning (if needed).

I'm thinking I may have a gas leak - I get crappy economy, like 18mpg @ 80% highway. How can I check this?

 

Sounds like you poor MPG may be due to the things I just mentioned. I wouldn't wait Also you may want to check your o2 sensors. You can have a shop run a diagnostics check to confirm.

 

A diagnostics check - if I'm not throwing codes, what is it checking?

 

Any other suggestions? When I accelerate from a stop, seems like the car doesn't move until the tach reaches like 1.8k rpms, as if there is a dead range. Still have not done the plugs yet.

 

What color is the smoke? More of a white'ish like vapor, or darker like burning oil?
Sounds to me like you have a few problems, probably not just one thing wrong. As for the jumping idle, I had a similar problem when my air filter bracket (plastic pos) broke and I was running without an air filter basically. The filter was just hanging down letting a free flow in. It caused me to get crappy MPG and the idle was jumpy at the idle as well and when it down shifted (automatic). Might be something to look into...a large air leak upstream of the MAF. I also didn't throw a code with this either...for a week!
As for cleaning the injectors and fuel system, Lucas makes a good cleaner in a little bottle. Basically can pick it up at any parts store. I wait till I have about half a tank left then put it in and run it down till the gas light comes on to give it a more concentrated effect. Costs about $8. I would do this BEFORE changing the spark plugs though.

The smoke is something I'd be concerned with. If you aren't throwing any codes though (with as many as these cars have)...it actually might work in your favor to ask one of these guys where something like that could go wrong that the sensors wouldn't pick up. I know that is obvious but I'm just trying to help narrow it down or throw some more ideas out there.

Might check this out as well. https://g35driver.com/forums/engine-...g-exhaust.html

 

time for basic tuneup. Check around on the forum for the basic maintenance schedule and make sure to take care of all those things first. HOpefully that helps the issue