poor idle
 

:confused: hey guys i have a 1994 bmw 740i i bought my car a month or so ago. when its cold outside i go to start my car and it idles poorly and the check engine light flicks on until i hit the accelerator then it turns off! what does this mean i bought a code reader and it said lambda control 1 and 2 but i reset the codes to see if it was an actual problem and now i read no codes any ideas could my oxygen sensors be bad?

Re: poor idle
 

O2 sensors due not effect cold start.
Rough cold start idle is most likely caused by vac leaks. The intake manifold seals are famous for leaking on this car-also check for cracked vac hoses, boots, etc, etc.

yes but if it was the intake manifold it would run poorly all the time not just when starting

Vac leaks
 

Wrong
In order for a cold engine to start and run properly it must have a rich mixture. If there are large vac leaks you have a way lean mixture.
A warm engine does not need as much fuel as a cold engine, that's why it runs better than when cold.It will still be lean but the o2 sensors and control unit will adjust the mixture to a point.
If there is a large enough vac leak the o2 sensors will reach there control limit and trip the check engine light.

Check for vac leaksSmileWavy http://www.pelicanparts.com/support/smileys/pint1.gif

More Idle Notes
 

In addition to the last observation, vacuum leaks can vary with the temperature of the components.

Another place to look is the "PVC" valve on the back of the intake manifold. They get erratic, leaky, and give those symptoms.

Have fun! Larry F. (ex-540i/6 owner)

yes but could it be bad o2 sensors my caode reader says they r bad even after i clear it and does anyone know where the o2 sensors r located on this car?>

O2 some more
 

You may or may not have bad O2 sensors - and, they are a 60K to 100K mile consumable, so it is not unusual to need them. The *main* point is that they are *not* the likely cause of your bad idle. They are in the exhaust system immediately in front of the cats (you have 2 or 4, I forget). How many miles on the car? And, are you aware of the Nikasil/Alusil engine block issue with this V8? Check out:

http://www.koalamotorsport.com/tech/misc/v8shortblock.htm

You can hope you have the Alusil block already . . .

Larry F.

larry i have 102,000 miles on the car and it only idles rough in 20 degree temps when i first start it otherwise it idles and runs fine!

"Shrug"
 

Hi, evanjoy.

No other inspirations. Did you check the link on the V8's? I sincerely hope you have the Alusil block.

Later,

yah i am good with that alusil thing my car is thanks for the link