On occasion my '05 G35x will randomly stop accelerating when in gear. Engine continues to idle. Usually, turning off the engine and restarting will fix the issue, but it will happen again and has 4 times in the last two weeks. Check engine light is on. It throws a P1238 code. After the fourth incident, the car still restarted, but to get it home the last 1/2 mile, I had to keep it in gear and basically drive it home on momentum. Engine continued to idle, but never would accelerate. It'll move in drive at about 2mph. After that half mile, the battery died. Over this time, I also had a periodic battery warning light appear in the dash. Some days it wouldn't appear. There may be some holes in the exhaust system as it is in need of a replacement. Haven't tried resetting the throttle body calibration yet or gone through the accelerator pedal reset procedure. Should I bother or is it likely something else? Wondering if I need a new throttle body. One mechanic seemed to indicate he had experienced this issue with others but doesn't do this particular repair work. He couldn't think of the name of the part, but said whatever it is it isn't feeding the proper signal from the accelerator to the engine. After recharging the battery, I've been able to get the car to accelerate in drive, but as I said, it's a periodic issue and I've avoided driving it much at all since.

Most of what I've been able to find online points toward replacing the throttle body assembly (aka the electric throttle control actuator). Anyone agree/disagree?

 

After going through the pedal accelerator reset procedure successfully, the check engine light has gone away. The battery warning light will still come on and go off periodically. For a split second, the AT Check light flashed upon ignition, which is a new one. It doesn't stay on. Heard a new sound coming from the area of the alternator. This is also periodic and couldn't be reproduced the next day: a scratchy sound that sort of sounds like a quietly squealing belt. Is that the alternator going? Since resetting the pedal accelerator, the car has been running fine otherwise. Haven't experienced the failure to accelerate in gear again... yet. But I'm also still running on a fully charged battery (used a battery charger and haven't run the car enough to know if the battery is being charged by the alternator yet). Will be driving it short distances to and from work and will check the charge on the battery periodically to determine if the alternator is still functioning properly.

 

This is probably all related to low battery voltage, start by fixing the charging issue.

Disconnect both battery cables, disconnect and clean (wire brush and a tiny bit of electrical anti-oxidation grease) the cable ends on the alternator, reinstall those. Next the main engine bonding jumper on the right side of the timing chain cover, the other end lands on the chassis under the coolant reservoir (it's a larger gauge wire, chassis side is a 2-hole lug). Lastly clean up EVERYTHING on the battery, the ground cable where it lands on the chassis next to the battery, the fusible link holder as well.

Then put it all back together and see if the charging system works properly.

 

Did you ever resolve this issue? Having the same problem but with 05' MT coupe