Rough idle when cold
08-17-2006, 05:40 AM
#1
Burning Brakes
Thread Starter
Rough idle when cold
Hey guys,
I've had this problem for some time now. When I first start the car in the morning, the idle is perfect and the a/f ratios (AEM wideband) are on the rich side (normal for cold start). Car idles fine for about 10 seconds, then a/f ratios go way lean and the idle drops way down, then a/f ratios richen up and idle returns to normal. Idle and a/f ratios continue to cycle up and down for about 1 minute, then car idles and drives like a dream once everything's warmed up a bit. I'm running an MAF w/ fuel controller yadda yadda...but I don't think that's the problem. I've tried adjusting fuel and it makes no difference to this cold start problem. I've replaced the idle stabilizer valve, I've installed a different DME. Can't seem to solve it.
Has anyone else ran across this?
Thanks.
I've had this problem for some time now. When I first start the car in the morning, the idle is perfect and the a/f ratios (AEM wideband) are on the rich side (normal for cold start). Car idles fine for about 10 seconds, then a/f ratios go way lean and the idle drops way down, then a/f ratios richen up and idle returns to normal. Idle and a/f ratios continue to cycle up and down for about 1 minute, then car idles and drives like a dream once everything's warmed up a bit. I'm running an MAF w/ fuel controller yadda yadda...but I don't think that's the problem. I've tried adjusting fuel and it makes no difference to this cold start problem. I've replaced the idle stabilizer valve, I've installed a different DME. Can't seem to solve it.
Has anyone else ran across this?
Thanks.
08-17-2006, 09:35 PM
#4
Burning Brakes
Thread Starter
My vacuum readings at idle (when warm) are 18 in. Hg. which I think is pretty healthy. Yes, I stole the air temp sensor out of my stock afm, and installed it into the MAF. It's wired straight into the old AFM factory plug.
08-17-2006, 10:38 PM
#5
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Hi Ian, does your idle fluctuation coincide with transition from open loop (cold start is open loop) to closed loop (DME trying to dial in 14.7 via o2 sensor feedback).
I have noticed that with my MAF there is more fluctuation in the air flow signal at idle than from the stock AFM. This makes it a bit harder for closed loop to zero in on 14.7. I think the idle stabalizer exaberates this problem, as leaner air fuel results in lower idle rpm. The idle stabalizer adds air in an attempt to lift the rpm, this makes it leaner again, and hey presto the DME overcompensates in the other direction resulting in a/f being too rich. Thats my theory anyhow.
What i did to counter this was to raise my idle a little to 950-1k rpm where the signal is cleaner in addition to flattening the signal in the idle area (0-0.6v) with my piggyback.
hth
I have noticed that with my MAF there is more fluctuation in the air flow signal at idle than from the stock AFM. This makes it a bit harder for closed loop to zero in on 14.7. I think the idle stabalizer exaberates this problem, as leaner air fuel results in lower idle rpm. The idle stabalizer adds air in an attempt to lift the rpm, this makes it leaner again, and hey presto the DME overcompensates in the other direction resulting in a/f being too rich. Thats my theory anyhow.
What i did to counter this was to raise my idle a little to 950-1k rpm where the signal is cleaner in addition to flattening the signal in the idle area (0-0.6v) with my piggyback.
hth
