beaSSt

As the title states, after installing my longtubes with catted y-pipe I seem to be running really lean at idle.

The STFT will continue to climb to +15 - +20 and the LTFT max out at + 25 at idle. When I start driving the STFT drop back to normal where they run between - 3 and + 5. As I drive the LTFT drop back as well.

Any thoughts as to why this would be so lean at idle?

SSpdDmon

iTrader: (10)

Most likely a leak (if it's just a few mods like you say). Are you sure you got a tight seal at the head and any other connections around the O2's? Are the O2's in snug with no room for air to get in? Do you hear any ticking when you get on the gas?

beaSSt

I do hear some slight ticking although it's hard to tell if it's wind noise at times. What would the ticking be?

Frost

iTrader: (45)

...a header leak.

jimmyblue

iTrader: (11)

More likely the headers just cool off the gas to the
point that the O2s are not staying "lit", a sleeping
O2 sensor output looks like lean and you get false
trimming to the rich side. This is why people say
"headers make you run rich".

You can try a pair of new sensors, move to 'vette
rears maybe; fresh sensors are less fussy about the
heat and work better when below ideal operating
temp.

KRAZY K 2000 TA

iTrader: (5)

i put new sensors in and its way better.banks are alot more even during scanning

NHRAMAN

iTrader: (1)

Which sensors..vette 13111's ????

98A4LS1

iTrader: (1)

Yep, Bosch 13111. Although, my driver's side 13111 is less than 3 months old and switching slow already.

beaSSt

An update -- the idle / fuel trim issues were due to a leak around the EGR pipe in the intake manifold. The o-ring wasn't seated properly.

I thought that I could hear an air whistle under the hood so I started investigating. I found it by going over every potential source of unmetered air and wrapping each with a shop towel to see if i could hear anything. As soon as the towel was wrapped around the EGR pipe the noise stopped.

The STFT and LTFT were reacting to the air that was being sucked in after the MAF and TB. Reseated the o-ring and everything is back to normal.

SSpdDmon

iTrader: (10)

Glad you found it.

ninobrn99

iTrader: (8)

now get rid of the egr