So troubleshooting an issue, my 2006 shinka drives fine but when i come to a light or a stop 9/10 times i'm stalling out or the rpm's drop to 200-500 rpm and then surge up to almost 2000rpm however the car starts back up just fine and i can keep going...

attached are my trouble codes, i can't seem to find any leaking hoses or anything under the hood at a glance, i just replaced the alternator with a 250amp one and so i know it's not a voltage issue causing this at least i don't think so.. does anyone have an idea on what to check? My engine was rebuilt by TREX Performance about 10-15,000 miles ago and I've been only using Idemitsu oil and have a sohn adapter for fresh oil.

 

Have you done any work on it recently?
Many times the rough idle issues are vacuum leaks, aftermarket intakes like K&Ns are trouble.

 

The only work I've had done to it was the rebuild, this cropped up since then on its own, only oil changes had been done to it besides the alternator which was done last weekend and the problem was already there I have a straight piped exhaust and the air pump has been removed and blocked off with that custom block plate. Stock air intake as well. I've ordered an OEM gas cap to see if that does anything as well.

I'm not seeing a whole lot of vacuum lines on this car to start tracing potential leaks on to be honest, i'm not hearing anything besides the air going through the UIM. I'm trying to figure out what i can before taking it to RPM in Hagerstown and spending an arm and a leg at a specialist.

uploaded the invoice from trex performance for everything they did to my car at time of rebuild.

 

It sounds like you have a large EVAP leak
Start by tracing that one, then the rest of the vacuum hoses. You can google for a vacuum diagram to help find the hidden bits under the UIM, throttle body, etc.

Is there oil in your intake or on the MAF sensor?

Another way to confirm it's a vacuum leak issue and not something else is reading the airflow grams/sec from OBD2 while the car is warmed up and idling around 800rpm. It should be 5ish g/sec, if it's much lower, that confirms you're letting in unmetered air.

 

@Loki , I've checked the obd2 reads for the meter, it's reading about 0.5-0.6lb / min which i converted to 3.77-4.53 grams per second at about 830rpm ... does this seem within spec? it doesn't seem to be to me... I'm going to be tearing apart the intake to check for oil in the intake on or in the MAF as well

 

Your evap purge valve may be stuck open.
If you have a scan tool, use your scan tool to command it open/close, your engine should sound differently
or
Remove it and manually block the vacuum hose, if your engine runs better and maf reading goes up your evap purge valve has failed.

 

4.53 is kinda low. Ideally you want 5 to 5.5 g/s.

 

Shaozhou, I have a BlueDriver OBD2 tool, not sure if I can command it to open or close i'll check.

Looking at this: https://www.rx8club.com/series-i-tec...iagram-214910/ is the Evap Purge Valve the part that's listed as Purge Solenoid Valve or is there a picture or somewhere I can use to show me where this part is located?

 

Replacing the fuel cap fixed the large evap leak. however i'm still needing to know if the purge valve solenoid is the evap purge valve in recommended by @Shaozhou Zhang to replace as i did order it... also I've replaced the downstream O2 sensor already yet it's still showing a code for the high voltage. is there anything else i can do about that? Would that be why it's running lean? thanks.

 

The downstream O2 doesn't really control mixture, it's more to validate the cat performance. So it's not why you're running lean, but the high voltage code means there's an electrical problem. Sometimes the wire to that O2 sensor gets pinched when reinstalling the trans or the exhaust. See if you can trace the wire.

But the airflow being low at idle confirms you're getting unmetered air in somewhere. So a vacuum leak. Like I think I said earlier there's bunch of stuff out of sight under the UIM and throttle body that could e responsible.