Hani08G37Coupe

Hello guys, I am a new member and also new to the G37 VHR world. So I have searched the forum up and down and need help chasing down a weird issue that recently started with my car. So to start, the coupe is completely stock except an muffler delete. I am current on maintenance and use all high quality fluids. The car has 140k miles and has never had an issue. The idle seems just fine and power is still pretty good. No check engine light yet. When cruising at a steady speed and then slightly roll into the throttle, the car will hesitate and stumble a bit. Once in a while it will make a small backfire under the hood under the same scenario. It has new oem plugs and filters. Run 93 gas. I have cleaned the mafs and the throttle bodies.
Any ideas or suggestions? This hesitation/ stumble is driving me crazy.
Thanks!!
Hani.

CJ1957

Having cleaned the throttle bodies recently, you might need the perform a Idle Air Volume Learning (Throttle Position Learning) to correct your issue. Even if you haven't cleaned the TB's you should perform the process anyway. I would suggest performing all the re-calibration protocols to insure you cover all the bases. Written instructions are below but also here's a video:


Resetting The Throttle Body Calibration:
A Rough Idle or a SES can sometimes be caused by a change in the throttle body position sensor calibration. To correct any accidental changes in throttle body calibration, use these procedures to re-calibrate. Note: These procedures are a little tricky to do. You must get the timing just right. Use a stop watch to help the precision of your timing.

Accelerator Pedal Release Position Learning Procedure.
Make sure that the accelerator pedal is fully released.
Turn ignition switch “ON” and wait at least 2 seconds.
Turn ignition switch “OFF” wait at least 10 seconds.
Turn ignition switch “ON” and wait at least 2 seconds.
Turn ignition switch “OFF” wait at least 10 seconds.

Throttle Valve Closed Position Learning.
1. Make sure that accelerator pedal is fully released.
2. Turn ignition switch is “ON”.
3. Turn ignition switch is “OFF’ wait at least 10 seconds. Make sure that the throttle valve moves during above 10 seconds by confirming the operating sound.

Idle Air Volume Learning (Throttle Position Learning) It's best to time with a watch/clock.
1. Perform “Accelerator Pedal Released Position Learning”.
2. Perform “Throttle Valve Closed Position Learning”.
3. Start engine and warm it up to normal operating temperature.
4. Turn ignition switch “OFF” and wait at least 10 seconds.
5. Conform that accelerator pedal is fully released, turn ignition switch “ON” and wait 3 seconds.
6. Repeat the following (steps 7a, 7b) procedures quickly five times within 5 seconds.
7a. Fully depress the accelerator pedal (HARD)
7b. Fully release the accelerator pedal.
8. Wait 7 seconds, fully depress the accelerator pedal and keep it for approx. 20 seconds until the Check Engine Light (CEL) stops blinking and turned ON. .
9. Fully release the accelerator pedal within 3 seconds after the CEL is ON.
10. Start engine and let it idle.
11. Wait 20 seconds.
12. Rev up the engine two or three times and make sure the idle speed and ignition timing are within the specification

Hani08G37Coupe

Thanks CJ1957. I will run through all protocols this evening. I will follow up with results.

ILM-NC G37S

iTrader: (3)

6MT or 5AT?
How is your engine idling? 650+/- RPM or does it occasionally hang up around 1000-1050RPM?

Hani08G37Coupe

Idle speed seems to be ok and normal. The issue only happens when slightly rolling into the throttle under load low rpm. It’s like a stutter or sometimes a quick intake backfire sounds like. Car is a 5at.

Hani08G37Coupe

I have noticed a slight rattle from under the car when warm for Awhile. Wondering if I have a Cat going bad. Going try and check it tonight.

Hani08G37Coupe

Ok here is the latest update. I performed all relearn protocols and issue still exists. Checked both cats and they both checked out ok. Next thing to check is fuel pressure once hot. I wonder if once the car has been driven for awhile, the fuel pressure drops a bit? Possibly a fuel pump slowly checking out. Seems the stumble only happens once driven for several miles. Still Idles, starts perfect every time.