528i Funky Idle on Start Up

Freddy · Post by **Freddy** » Tue Mar 09, 2010 3:42 pm

hey, Josh. Frustrating adventure you got going. Have you tried unplugging the idle switch at the throttle to see if the surging goes away? I am wondering if it could be fuel shut off surging?

JoshInAtlanta · Post by **JoshInAtlanta** » Wed Mar 10, 2010 7:26 pm

I replaced the AFM this evening and the car is acting much different now...

Not sure what's going on.

I wasn't sure how to describe it, so I grabbed my cellphone and took a crappy video... but at least you can somewhat see the tach and hear the motor revving.

Freddy · Post by **Freddy** » Wed Mar 10, 2010 11:18 pm

I watched you video. Thanks for posting that - I love technology. Very helpful to be able to show the problem. And yep, that sounds like classic fuel shut off surging. You can prove it by unplugging the idle switch. If it stops surging, if it is fuel shut off, then you will find that the idle is above about 1200 rpm. The solution is to reduce idle speed to below 1200 rpm. Try 1000. Then re-connect the idle switch. If no surging, then you are on the right track. Sometimes, cold idle will have to be adjusted with the aux air valve that I see you are already familiar with. You don't want cold idle to go above 1200 rpm, or you will get surging until the engine is warmed up and the valve closes a little. The fuel shut off theory is explained in detail in the L-Jetronic Throttle Body Adjustment FAQ. I really hope this helps. Good luck!

JoshInAtlanta · Post by **JoshInAtlanta** » Thu Mar 11, 2010 12:44 am

Freddy wrote:I watched you video. Thanks for posting that - I love technology. Very helpful to be able to show the problem. And yep, that sounds like classic fuel shut off surging. You can prove it by unplugging the idle switch. If it stops surging, if it is fuel shut off, then you will find that the idle is above about 1200 rpm. The solution is to reduce idle speed to below 1200 rpm. Try 1000. Then re-connect the idle switch. If no surging, then you are on the right track. Sometimes, cold idle will have to be adjusted with the aux air valve that I see you are already familiar with. You don't want cold idle to go above 1200 rpm, or you will get surging until the engine is warmed up and the valve closes a little. The fuel shut off theory is explained in detail in the L-Jetronic Throttle Body Adjustment FAQ. I really hope this helps. Good luck!

Thanks for the advice. Reading that really helped... I will try this tomorrow!

Lenny D. · Post by **Lenny D.** » Thu Mar 11, 2010 1:00 am

Freddy is correct.

JoshInAtlanta wrote: I also cleaned the AAV one more time and adjusted it so it is more than half open.

You have the classic case of the over-adjusted AAV during warmup (which starts immediately after startup). Reduce the opening (slightly) until the surging stops (takes time over cold-warm cycles). Then readdress your poor warmup complaint.

JoshInAtlanta · Post by **JoshInAtlanta** » Mon Mar 15, 2010 2:09 pm

Replaced the AAV with a unit out of a parts car and my idle is stable now. Still have the spare AFM installed, but it seems to be ok. It started right around 1000 RPMs, dropped down to somewhere between 800-900 for about 5 minutes, then settled right around 900 until I shut it off.

Still going to tinker with it more, but it seems like it is much better now.

Lenny D. · Post by **Lenny D.** » Mon Mar 15, 2010 9:59 pm

You're welcome..........

JoshInAtlanta · Post by **JoshInAtlanta** » Mon Mar 15, 2010 11:45 pm

Lenny D. wrote:You're welcome..........

Yes yes, thanks!

I'm not done yet, but since I have no seats in the car, I can't road test it. Hopefully this weekend I can roll it out into the driveway and at least get some good time on it to see how it warms up.

I think it's pretty much dead on though, but we'll see!

Thanks again.

1st 5er · Post by **1st 5er** » Mon Mar 15, 2010 11:47 pm

I love it when a plan comes together...

Finally!!!