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Air fuel ratio at idle

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stealth13

10+ Year Contributor
136
0
Oct 10, 2008
calgary, Alberta_Canada
What should my air fuel be at idle? When I turn it on it goes from 13s to 15s and after about 30 seconds it goes past 18 and I can no longer read it, at this point it idles bad and throws an engine misfire cel

Someone please tell me what it should be at?
 
You want it at 14.7 at idle. As to why you are running lead is another question, if you want an answer tell us what kind of set-up you have.
 
Idle should be around 13 to 14 depending on your set up. Mine is set at 13 when the car is setting still and just idling because if I make it much leaner, it idles like crap.
 
The car should go into closed loop at idle and that causes the AFR to cycle on either side of 14.7:1 where the O2 sensor switches from lean to rich and back.

If your doesn't then it's having some problem going into closed loop.
 
If your car starts leaning out idling that means your motors get way more air than your MAF is accounting for which means theres a "boost leak" in between your MAF and the head. Do a boost leak test and fix your leaks because one of them is really bad.

:dsm:
 
I'm having same issue. My mods are up to date, didn't want to start another thread for it. I have dsmlink v3. Still trying to learn the program. I will check on boost leak since I doubt the shop did after last mods.
 
Some car's just run lean at idle. My car runs lean at idle, with zero boost leaks. Same with my buddy's car. As for it misfiring and running like shit, I would start troubleshooting, boost leak of some sort perhaps.
 
Mine does the exact same damn thing. My car has no damn boost leaks or anything. My set up is 255 welbro, 550 RC injectors, arromotive Fuel pressure regulator, 16g, Maf trans with 3gm sensor, full echaust from header back, Still cant figure out whats going on.
 
Mine does the exact same damn thing. My car has no damn boost leaks or anything. My set up is 255 welbro, 550 RC injectors, arromotive Fuel pressure regulator, 16g, Maf trans with 3gm sensor, full echaust from header back, Still cant figure out whats going on.

Do you have a wideband LOL?
 
Mine was doing this once and the exhaust studs going down into the turbo from the manifold where finger tight. I must have forgotten. I would be at idle initially for a couple seconds then go to 18s on my wideband then off the top and if I used DSM foot I could keep it alive forever. I tightened the four bolts and the problem never returned.
 
I have mine set to 13.3~13.6. I run bc 272 cams with the exhaust cam retarded 3*. 14.7 and it runs like crap. I also run in closed loop till around 2000 rpm. Just seems to run better that way.
 
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