running lean at idle.. need help

[jcold83]

So I've been working on putting a rebuild motor in my car. Everything went well put it in and started up first try. But when I first start it,runs good with good air fuel ratio. Then about a minute later it goes way lean and between the gm maf and safci cannt get it to get off lean. I've switched o2 sensors throttle bodys cas sensor, even took off the gm maf and switched to my stock maf. Nothing... any ideas...

 

[werx]

Are you running stock injectors and fuel pump?

 

[gofer]

Do a boost leak test instead of replacing parts that aren't bad. The reason why your AFR's look good on initial start-up is because the ECU is still in open loop. Once it makes that switch into closed loop, which rely's on the MAF/o2 sensor to be accurate, it goes lean. Its probably a fairly good sized vacuum leak around the TB/IM area and won't be too hard to find.

 

[jcold83]

My compressor went bad yesterday so I didn't get to do a leak test. But I will try today with a new compressor. I have 550. Injectors and stock fuel pump..

 

[Absit]

Do you have wideband?

 

[SpoollinAwd]

How lean are you talking?
I would bet money that you do have a boost leak I had one when i replaced my motor took me al of 30 min. to find good luck man.

 

[T is for TURBO]

Could also be an exhaust leak giving you in incorrect reading.

 

[SpoollinAwd]

Yes but would have to be a pretty good size leak!

 

[jcold83]

So i did have 2 small intake leaks over all i was losing about 2psi. there is a small exhaust leak. Im waiting to get my new exhaust manifold in to fix it. But if i hold the gas pedal down to about 2000 rpm i can get a reading and kinda give it a tune at 2000 rpm with the safc. once in ahile the car will idle good for about 30 seconds and then it just seems like something kicks on and it stops idleing. I checked to see if it the fans kicking on but its not.Any ideas... this is driving me nuts...

thanks

 

[romeen]

What are your actual AFR numbers at idle?

 

[jcold83]

Its off the scale. When i first start it, it runs a little lean at 14.0 then goes to 15 16 18 and then it stops reading..

 

[romeen]

Just curious what the location of the sensor is? Before or after the DP flex section? Do you think it's giving you accurate numbers when driving around?

 

[jcold83]

its before the flex pipe. Yea i think its in a good location, ive had it there for about 6 months before doing this motor swap. Only after the motor swap im having problems..

 

[T is for TURBO]

Yes but would have to be a pretty good size leak!

Not really. I just had this same problem the OP is having. I would start the car and it would be fine for about 30 seconds. After that, my AFR at idle would go WAY lean. The AEM unit pegged out as did ecmlink. I got under the car and there was a small leak at the gasket right infront of the WBO2 sensor. I fixed the leak (mostly), now at idle is sit at about 14.7-15. Exhaust leaks can throw your AFR off more than you might think.

 

[Chrispy0530]

So was this ever resolved?? I'm having this same EXACT problem that just appeared out of no where. Car overheats while at idle when the WB starts going lean. I set the 02 to constant open loop mode, and it doesn't run AS lean. It's still a bit lean at idle, but not as much. It's roughly 16-16.5 instead of 17 and beyond what the gauge can read.

 

[gofer]

Logs are always useful and will show us exactly what the cars doing, if you've got the option to capture a log and post it you should.

 

[Chrispy0530]

Oh, right. Well, I'll show you a thread that I started that has various logs.

http://www.dsmtuners.com/forums/tuning-engine-management/409020-running-lean-issue.html