Thread: ltft causing lean idle

When I look at my log file I can see a correlation between the wideband and ltft. Im going lean at idle in closed loop. For instance my wideband will be at 16to18 when the ltft is -3 to-7 and when its is near 0 the afr goes close to stoich. When cruising the afr is fine. Also why would the afr be commanding 10.3 in pe when the pe tables are set to 11.7?

This 3800 is in a 5speed fiero with xp cam, 3.4, slp headers open downpipe

If commanded doesn't match actual you have a overally rich or overally lean MAF curve.

In your case assuming everything is working correctly, your MAF curve is too fat up top. If the AFR on the wideband shows 10.3 but the commanded AFR is 11.7 you need to remove fuel via the MAF curve to make them match. Remove 5% at a time, say above 7,000hz and try and lean it out. Make sure to keep the curve smooth still, no large dips where you remove fuel.

I am running better in closed loop idle not great but more consistent. The first 30 seconds of the idle is in open loop and its running super lean 18-20afr what do I adjust for this? startup afr in p/e or open loop idle afr adjustment by rpm. I have used a smoke machine to check for vacuum leaks but all seems well. My gut says there is something not reading accurate or something in the tune is wonky. Any replys are appreciated.

Try adjusting the open loop AFR and AFR adder for open loop to see if you can get the fuel mixture richer. Something seems off it's really that lean at idle on cold start because it's normally always a rich mixture based on the commanded open loop tables.


Not sure what you tune with but log files and the tune can be helpful to look at.

Open loop base af based on coolant temp is 12.39 Added 10% to the startup enrichment afr This made openloop a lot better it hung around 14.7. Closed loop was not so good it is ranging from 10-20 afr. It is slowy going from lean to rich almost like the ltft is trying to play catch up.