[SOLVED] High STFT at idle but when I bill the throttle it goes back to normal.

Ok so I’ve been tracking down a fuel trim problem. When sitting at idle sometimes my STFT’s jump to 25 but when I blip the throttle it goes back to normal. When I’m driving the STFT’s are back and forth but not quite as bad, and when going back to idle after exiting the freeway the RPM’s hunt 1500 to 300 RPM until I blip the throttle and then it goes back to normal.

I’ve smoke tested the intake, I’ve checked the purge valve, I’ve fixed a few small leaks but nothing that made a significant difference. I’ve checked the brake booster, the MAF sensor, I don’t think it’s the O2 sensor as it is brand new but is a possibility.

I’m not sure what else to check, I can post datalogs if that will help just let me know.


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Did you do a boost leak check?

 

Yes I smoke tested the entire system


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Not the same thing

 

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Year/Make/Model:
Mileage:
Location:
Concern:
DTC's:
Modifications
ECU/Tuning Software:
Tuner:
Is the concern intermittent?
Can you duplicate the concern?
Recent Repairs:
Correction:

 

Yes it is, and I’m not having problems with boost I’m having a problem at idle.


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Please explain to me what a boost leak check is.


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2008 Mazdaspeed 3
111000 miles
Houston Texas
Likely has a vacuum leak, fuel trimes max out and it runs lean and then when I blip the throttle it goes back to normal. When I’m exiting the freeway and get out gear the engine hunts to find idle until I blip the throttle.
P0300random misfire, p2188 fuel rich at idle, p2187 fuel lean at idle
CST4, Cobb intake, 3 inch catless exhaust all the way through, 3.5 bar map sensor, Grimmspeed 3 port EBCS, VTCS deleted intake manifold.
Cobb Accessport currently being tuned by Will Dawson of PD Tuning
The concern is intermittent but highly repetitive
I just installed all parts above but had this problem before installing the parts and was hoping it would work itself out.


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Here you go....

https://mazdaspeeds.org/index.php?threads/how-to-boost-leak-test.6276/

 

Just like I though, same thing. I just added smoke so the leaks were more visible.


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Look at the video the other guy posted, definitely the same thing.


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They are not the same, perhaps you should do some research on the purpose of a boost leak test vs smoke test.

Hint, you can pass a smoke test while failing a boost leak test.

 

Look man I’m not here to discuss that, I’ve done what the video did I just added smoke to the pressure. Trust me there are no leaks. I’m thinking I have a stuck one way valve or something. My first thought was the purge valve, but that’s not it.

Also I’m not having a boost problem whatsoever, my fuel trims in boost look really good and feels fantastic on acceleration. I’m trying to fix the idle problem I’m having so I can continue with my tune.


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So what is it leak or no leak? Lol

Because a boost leak test will find vac leaks as well ( should be done at 10psi above your intended boost target). No a boost leak test is not the same as a smoke test, yes you can use smoke while the system is pressurized but my understanding that's not as good as bubble checking due to the surface tension vs pushing smoke out the way.

How far into the tune are you? Did this start after a revision? What's will have to say about this? He's excellent at what he does and definitely worth touching base with if you haven't already especially during the tuning process.

Have you cleaned the throttle body? Wonder if it's sticking.
Have you tested the PRV and cleaned the spill valve? I wonder if it's a little stuck but at higher pressure opens fine.

 

Yea man pressured it up with bubbles and added smoke. I did find some leaks but nothing significant. I had the problem before and after I did any modifications, I was hoping when I had the engine out and and making repairs and adding my go fast parts it would sort itself, but it didn’t.

I’m not having any problems during wot at full boost, I’m having problems at idle. It feels like a vacuum leak but it’s acting like a sensor and not giving a code for said sensor. I’m really stumped and frustrated dude this has been hard to track down.


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I can appreciate that I just went through and had some frustrating leaks including the oring on my vvt solenoid had to do a new VC and oring there.

The other thing I've noticed is every so often I have to replace my MAF sensor o-ring.

Just to confirm when you did your leak test you had the VC breather to intake blocked off right?

 

I haven’t cleaned the throttle body, but my logs aren’t showing that it’s sticking. But I think that might be worth looking into.


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Yes sir I did. What’s weird is that it runs rough at idle, I blip the throttle and it works perfectly and I can take some logs if that will help.


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Check the battery

 

Battery is most definitely good. At one point I did think low voltage could be an issue but I ruled that out for sure. Battery holds 12.5 to 13 and alternator puts out 14.2.


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What brand MAF sensor and O2 are you running?

 

Stock MAF and the NTK o2 sensor (I believe that is the stock sensor from rock auto)


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