Hello again g35 experts,

I am having a new problem with my 2003 g35 coupe. I just hit 150,000 miles, and overall besides the regular things that go bad, this car has run pretty darn good. For the longest time this car has eaten oil like crazy. I am in Louisiana in the heat and i use 10w-30 royal purple for the longest time. Lately the car has been idling rough and ever since I replaced the alternator and starter last week it was a little better...

What is happening is I am driving along at 3k rpms & and when I push in the clutch and brake to slow down, the rpms literally almost go to zero and then bounces back up. I thought originally maybe it was the alternator not giving enough power to the car. I have a brand new optima battery that is 3 months old. I am at a complete loss as to what is causing it. When the car engine is cold it does not drop to 0 like when the engine is completely warm and i have been driving for a few miles. Also, when the A/C is on that seems to keep the rpm's from dropping to almost 0 also. And the oil psi goes up 2-4 points when i engage the a/c.

Also, the oil pressure drops directly in relation to the rpms and i can tell when the car is around the 20psi level, the oil is low. On a fresh oil change the psi is 30-34 with the engine completely warmed up. When I am sitting at the red light idling the psi is around 28ish lately and only when i push the clutch in when i am driving and brake does the oil pressure drop to the low 20s and the RPMs almost go to 0 and then bounce back up to 500ish.

Could this be my oil pump or oil pressure switch causing this? I have recently cleaned my mass air flow sensor but could it be going bad? I took a video of it this afternoon so you can see it for yourself (may be kinda hard with the sun glare). If any of you gurus have an idea where to start, I appreciate the help. Thanks!

http://www.theoryevolution.com/g35stall1.mp4

 

for the oil, stop using that royal purple and use some conventional castrol.

 

+1.

 

Should i be using a thicker weight? I used to go with Mobil1 synthetic but when I switched to royal purple the engine definitely ran smoother. What about Amsoil? I use that for my gear oil and the car definitely shifts smoother between gears.

I ordered a new oil pump and pressure switch anyways. Can't hurt to put a new one on...

 

Those synthetics have a consistent molecule size as conventional has various sizes that wont slip through as easy. Royal purple probably uses friction modifiers allowing the power claims they announce; which a
Probably breaks down easier than conventional, and is probably a syn blend as well.

 

interesting... I am going to get some castrol tomorrow. Is the castrol mineral based oil? Which i think is what the service manual states...

 

Think so. Change it at 3000 ull be just as fine.

 

Try swapping out the cam and crank sensors. Sometimes they have weird failure modes that cause these symptoms. Recently I fixed a g35 that had a completely random stall during shifts, it was a bad crank sensor but there were no codes. Sometimes it is best practice to replace both cam sensors and the crank sensor.

 

Thx. Just bought new sensors now. Hope that and the oil solves the problem....

 

Try crank first.

 

Just changed the oil to Castrol GTX high mileage and will report on the crank sensor when I install next week.

 

same thing happened to me on my 2003
i just drove around with the ac on at all times lol
then i did idle relearn and now its fine for the most part, except once a week it will happen once and go away.
if that doesnt help, clean your throttle body

 

My throttle body is clean, but i am putting all new mass air flow, crank position, and other sensors this week.. I will do the relearn and see what happens...

UPDATE Well chaning to oil solved the consumption problem. After new sensors it idles a little better. But i think it may be an air flow problem in the engine. I am going to put new gaskets and hoses.