Running Lean

[alphalanos]

I recently put a high flow cone filter on my car to replace the stock air box. Now when my car is idling it seems to be running a little lean. Is this dangerous? I can see the engine cycling unevenly sometimes, as opposed to running smoothly.

[MagicRat]

An idling car uses relatively little air flow, so a high flow filter makes no difference Chances are something else has been disturbed, either a vaccuum line is off, poor electrical connection etc.

[burly]

However, running lean can be dangerous yes (e.g. burned valves). So you should nevertheless investigate the problem to see what is causing it. It is probably something like a vacuum hose or sensor, as MagicRat stated, because if the ECU knows the engine is running lean, it will adjust the fuel rate to compensate (to a certain point), that is, if its a modern fuel injected, computer controlled engine. If its carbuerated, then its a hole different ball game. Replying with more specifics on the engine, intake and exhaust, will aid greatly in diagnosis.

[quaddriver]

Originally Posted by alphalanos

I recently put a high flow cone filter on my car to replace the stock air box. Now when my car is idling it seems to be running a little lean. Is this dangerous? I can see the engine cycling unevenly sometimes, as opposed to running smoothly.

seems? put it on a scan tool and look for the O2S cross counts. IF they increase at a rate that does not seta flag for being too slow, its fine.

Besides, at idle the air is metered by the IACM/ISC whatever your manu calls it. at best you will see a change in IAC counts with no flags set.

[KC Ron Carter]

here is some information on using a VOM to see if the car is running lean.

On the o2 sensor connect to the black lead from the sensor.

.6 volts is dang rich .3 volts is dang lean.

http://www.kemparts.com/TechTalk/tt07.asp

The system is normal when it overshoots rich and then overshoots lean continuing on as overshooting the perfect 14.7 to 1 air fuel ratio.

Later,

[alphalanos]

its a Daewoo Lanos 1.6L, FI, cone filter, and stock exhaust.