P0171 and P0174 Codes after Stillen CAI - Help needed
 

My car is a 2010 auto, with 12,000 miles on it. After installing my Stillen Gen 3 CAI everything was fine for several weeks. I almost ran out of gas (was headed to gas station) and was idling at a light. The RPMs dipped a bit, enough to notice and cause the engine to shudder a little (AC was on high) then came back up and threw a CEL. I was hoping it was just because I was so low on gas. After filling up, it didn't fix it. I read the codes and cleared them, but it came back. I have Dash Command and have monitored it and captured log files. Hoping someone here can read and interpret. I also have a FI exhaust installed but I don't think that has anything to do with it. Car is an automatic.

What it does:
- Throws a lean code (started ONLY on P0171 passenger side but is now doing P0174 as well). Only occurs when idling.
- Engine pulls strong - no issues, no shuddering while accelerating or cruising.
- CEL Happens over and over - pretty much any drive where I have to sit at a light for very long.

What I've done:
- Checked for vacuum leaks on intake. All hoses and clamps seem tight and good. CAI was installed for a few weeks with no issues at all.
- Cleaned both MAFs.
- Dumped in a bottle of Gumout REGANE fuel system cleaner (has not run all the way through the tank yet though).
- Logged the data with Dashcommand

Log file is here

Don't think it's O2 sensors - car only has 12K miles on it. Seems odd the issue started when I almost ran out of gas - could be coincidence though. If it was a CAI install issue I would think it would have popped up immediately and not waited weeks. So I have no idea. Hoping someone here does.

Thanks!
James

Reset the ecu

The car thinks you are running lean (P0171 = bank 1, P0174 = bank 2), based on exhaust O2 readings. Often caused by dirty MAFs or a vacuum leak. Since you have cleaned the MAFs, I'd check for leaks again. Since both banks are affected, I'd start looking at the MAF to manifold piping and the manifold itself.

Could be the O2 sensors but I doubt they would both go out.

If you try Elmo370z's ECU reset, don't be surprised if the windows start acting flaky - window reset procedure can be found on this site.

Edit: Wouldn't hurt to clean the MAFs again. Cheap and easy job.

I'll check the couplings again today and climb under the car to make sure my exhaust hasn't come loose or leaking. Did it again on the way to work while sitting at a light. The Short Term Fuel Trim was at 25% on both banks and went to 0% at the time it stumbled/idle dipped a bit. It's subtle and only last a second or so and then it goes away. Data logging on the Dash Command app is pretty awesome. Definitely coming in handy!

Thanks for the ideas - I'll post back so hopefully can help others.

James

Yes the windows were a pain in the *** to reset. Or go to auto zone and get the codes cleared.

?!?!?!?

It only takes 15-20 seconds to do the window reset and you don't have to leave the driver's seat. Maybe we're talking about different "window resets."

Clearing the codes won't do much good unless the problem has somehow corrected itself. Possible but not likely, IMNSHO. But, hey, it's cheap (OP's Dash Command app may be able to reset DTCs; $20-60 to buy an OBD scanner that will) and easy (a few presses of the buttons) so why not?

That info should be useful to someone that knows more about this than I do (I'm pretty good with cars from circa 1970 but modern cars are more of a collection of black boxes to me). Here's hoping one of the engine management gurus chimes in soon.

I wouldn't want to work on a Z (or any other recent YM car) without an OBD/CAN scanner. The ECM will do most of the trouble-shooting for you. With a scanner, the FSM, and this site, one can trouble-shoot just about any problem.

That's what this site is all about. :driving:

Ok - I learned a LOT about fuel trims. The Dash Command app along with a wifi OBD dongle from Amazon is amazing. Not only does it read and reset codes, it also logs anything the OBD is seeing and that includes short and long term fuel trims which is what I needed to watch. When I'd drive the car I could tell when it was going to throw a code because my short term fuel trim would be 25 for some time and then dip to 0 causing my RPMs to drop and stumble just a little. My short term fuel trim was 25% at idle meaning the car was running VERY lean. Your trims should be close to zero but can bounce around from 8 to -8 as the ECU compensates and tries to maintain a balanced Air/Fuel ratio. When I would rev the car the STFT would drop back to almost normal levels. At idle, back to 25. Definitely a vacuum leak. So I went back over all my intake piping and discovered the issue - a coupler had slid off of the pipe on the bottom where you couldn't see it and it was on the opposite side I had been looking. I didn't LOOK like it was off and the clamp was tight. But upon feeling all the way around it with my fingers I found it. After adjusting the pipe and re-tightening the clamp all my fuel trims were between 9 and -9 and mostly around zero. I think that was all it was. For some GREAT info on this check these pages out:

Fuel Trim?

P0171 and P0174 - OBD-II Trouble Codes

And get Dash Command if you have an iphone along with a wifi OBDII dongle. It is a great tool and resource.

:driving: