First post here so hello to everyone. I've found lots of useful information on this board so far. I tried searching for this issue on the boards but could not find anything similar to these symptoms.

I just bought a 2003 G35 5AT that has 164,xxx miles. The car runs really good, engine is quiet with no noticeable noise or unusual noises. My issue lies with the following. During normal driving the car shifts fine and performance is normal. The moment I want to get on it and floor it the car gets up ok until it reaches around 4-4.5k RPM and then it just slowing goes from there as if it was struggling. Same goes when it switches the gear to the next gear and reaches the same RPM levels.

I've already done an ECU reset using the Easy ECU reset method. Anyone have any ideas where to start? It just seems like this car is hiding power that I cant retrieve because its being hindered at the higher RPM range.

Ive been told MAF and spark plugs because it may appear I am running lean.

 

It could just be VDC kicking in have you tried turning VDC off and seeing if it persists?

 

It appears to do it with VDC off as well. I even went into manual mode. Thats how I determined more or less the RPM this was happening at.

 

I would start with spark plugs. When is the last time they were changed?

 

No way to tell. I bought the car used so obviously they aren't going to give you much history about it. I picked up a set of spark plugs today. Already changed out the air filter. Gonna change the oil tomorrow after work and throw in a new set of spark plugs and see what happens.

Had a guy from another board say possibly a bad ecu. I am hoping its not because that could be an expensive fix.

 

Hey do I get a guess?
At full power, & high RPM, it starts to lose power right?
If it's missing I would guess plugs / ignition.
AT 160K, I'm guessing fuel pump/filter!
I wounder where the filter might be? I should change mine to.

KP

 

Finally a 03 with very close mileage to me....

Firstly:

In these tests, what MPH are you doing? 0 - 60 ? or rolling?

I would first check air filter make sure the filter is relatively clean.

Mass air Flow sensors usually give problems at ALL RPM ranges.

Spark Break-UP can cause that situation for sure but if the people who had the car prior to you did proper maintenance then you'd be aware that the spark plugs are to be changed @ 100k RPM intervals.

So I would look into this as there is a potential that it could be overlooked.

Next up:

Does the car have a bit of hesitation turning on? If so look into your camshaft sensors.

If you experience LIMP MODE / SAFE MODE then Throttle Body is the next step.

 

Im pulling the spark plugs today. I bought some Bosch platinum but there seems to be mixed opinions on them working correctly on the G35 so I might go back and pick up a set of NGK platinum plugs instead to be sure.

I believe if I am not mistaken that the issue persists from 0-60 and while rolling as well. I do not have hesitation when turning on. The car starts with no problems.

I did change out the air filter which was filthy yesterday but the issue still persisted after the air filter change. I am willing to bet that the car has been neglected and I am also think that the plugs probably have not been changed out. I wont know till later this afternoon when I start working on it.

I'll keep you guys updated and try to get some pics of something looks odd.

 

These cars seems to like the NGK's. Either the Iridiums or the Platniums. I did OEM platnium with mine. They were toast at 111K miles.

Guy at my work just did plugs on his '03 Acura TL. 260K miles on original plugs. He had misfires on all 6 cylinders, but the car drove. He currently has 320K on it. now.

 

Thats isane!

Has he ever had any major issues with that car? If its still on the road and driving well that is a well built car.

 

Nope...just normal wear/tear like shocks, brakes, tires, etc.

There's actually a recall on the transmission but he refuses to go have it done because the car has gone 300K+ with no issues.

He has owned this car since brand new

 

No joy on the spark plugs. Besides oil residue around the threads from them not being properly seated from prior owner installation they came out good. I changed them out in either case.

Went on a test drive and the car still continued with the issue. I can describe it as when you get to WOT as a sputter and struggles to get up and go. Normal driving does not replicate the symptom. I am going to try fuel injector cleaner. I am thinking fuel delivery is a problem.

 

i have noticed a similar situation on my car, bought it pre owned too. but i looked under the hood and noticed my intake coupler has a tear in it next to the MAF so im getting that replaced, hopefully thats what it is for me. if not i am going to use Mechanic in a Bottle fuel additive, its a great way to clean out and lubricate everything. i used it on my old vehicle and it ran great! give that a try. keep us posted!

 

You need professional help here. I would suggest that you go to infinitihelp forum and raise your question there. some of these guys are real pros in that forum. You are less likely to get speculative answers like you get here.

 

Alright nothing I've done seems to have fixed the issue. Heres a list:

Air Filter Changed
MAF Sensor cleaned
Throttle Body Cleaned
Spark Plugs changed
Oil Changed with Mobil1 Synthetic High Mileage
ECU Reset

KingoftheRoad1 - I am going to give that place a go as well. I can't figure this **** out. I can only think of transmission fluid needing to be changed out and fuel issue somewhere. Im all out of ideas.