Lean idle?

[Dave]

Hey guys, we've been having a problem with the van lately. It idles around 16-17:1 and it misfires about every 3 seconds. If I keep the idle up or put it in Neutral it's fine. I've replaced the AIS, TPS and throttle body altogether with no luck. It does it when it's warm and cold. The long and short term fuel trims we're normal, both very close to 0. I've even reset all the values. Driving around town it sits pretty at 14.7's, under load it's actually quite fat still at 19psi boost and roughly 61psi static. Plugs are new too.

Any ideas, guys?

-Bryan

[86Shelby]

I'll bet that it's actually running quite rich at idle. Rich enough to cause the misfire, which fools the O2 sensor to see it running lean. At higher RPMs it's easier for the PCM to adjust the injector pulsewidth so it doesn't run rich.


Edit: Looks pretty mean with the intercooler there. Still two portholes short of a Buick.

[Kevin]

Maybe it's actually a transmission problem? Loading the engine too much at idle while in gear?

Leaking brake booster? Does it do it while in park and foot on the brake? Maybe another vacuum leak of some sort.

16/17-1 Is right about where my van will start lean missing at idle. Should be shooting for closer to 14.0 at idle. Rarely will a rich error on the sensor show up as a constant 16 reading, usually it will just go to the leanest value the gauge can show and flutter back to the richest.

[Dave]

Maybe it's actually a transmission problem? Loading the engine too much at idle while in gear?

Leaking brake booster? Does it do it while in park and foot on the brake? Maybe another vacuum leak of some sort.

16/17-1 Is right about where my van will start lean missing at idle. Should be shooting for closer to 14.0 at idle. Rarely will a rich error on the sensor show up as a constant 16 reading, usually it will just go to the leanest value the gauge can show and flutter back to the richest.

Good idea. I'll check it in park with my foot on the brake.

Anyone have any other thoughts?