I have a 2003 G35 Sedan 5AT. At times, when the car does its hard shift at 40mph and thereafter, it sometimes feels as though there is a slight delay before it properly goes into the next gear. So it feels like the car is struggling to shift gears. Any idea on what this can be? Thanks in advance for any help!

 

Check your AT fluid, do a drain and fill if it's dirty.

 

how old is it?
if it's like 80k+ miles.. it's not going to shift like Day ONE..

 

+1 on that for sure!!! I had a similar problem recently and drained and filled my transmision fluid and did a fuel system cleaning and WOW!!! Night and day. I have an 03 Sedan 5AT.

 

Apologies for straying off-topic but what exactly is this fuel system cleaning you did to your car? Is it something like putting Chevron Techron fuel treatment into the gas tank, or something more involved?

 

no problem. No it was something more involved. It was an aerosol can-like product called MOC. It cleans the carbon from the valves and injectors. The fuel system on the car is turned off and the engine is run for around 5-10 minutes using the MOC as the fuel source. My car has 123k miles on it, so I saw a huge difference after the cleaning, but like I said, I drained and filled my transmission fluid and installed an HR Y-pipe at the same time, so I wasn't quite sure what was responsible for what. My mechanic who helped me with everything said the fuel system cleaner probably made a big difference.

Whatever made the most difference, the car runs like a champ right now. Smooth shifting, strong acceleration, just all-around better. I may get better mpg, too. If you want I can let you know about the mpg in a week or so because I'm getting gas tonight for the first time since I had those things done.

 

Shift behavior is adaptive based on your driving and throttle position.

Sometimes it'll shift hard and 'clunk', other times it'll do a delayed slow shift.