Ok well I've searched around and cannot find the answer.
Truck is a 1999 Silverado 5.3L cammed, bolt ons, and a ss3600 converter.
A bit of information:

-It first started when my truck sat about 2 days with the weather around 20*. My truck has never seen weather this low before
-It wants to idle about 300 rpm and the brakes are mushy as hell
-My wideband is showing that it's getting fuel and I can hear the fuel pump prime like always.
-When the temperature gets around 130-160* my wideband suddenly shoots up to 17-19:1 AFR which has my super worried. After 160* it goes back down to normal around 14.7.

I've replaced the intake gaskets, tried running it without the MAF sensor connected, I've looked over most of the hoses, reseated the injectors, and I can't find anything.

The engine sounds like a go kart with the noise coming from the throttle body and there is a horrible ticking that seems to go away at higher RPM. Once I'm driving I have almost no issues, but it's at idle and on deceleration that my brakes get dangerously mushy and I have to 2 foot the crap out of it.

 

Year make and model might help....

 

1999 Chevy Silverado 5.3L
224/224 cam
42# injectors
stock intake
ss3600 converter
longtubes no cats

 

Does it still have the same issue/problem when the weather is warmer? Meaning with the truck fully warmed up, 32* outside temp = truck runs like crap, 60* outside temp = truck runs fine?

or

Does the truck run like crap as it is warming up, but once it is fully warmed up it runs fine?

 

Unfortunately, now it's all the time. It's 44* in the garage and it's still doing the same thing. I was able to get it to idle without two footing it one time yesterday after it was completely warmed up, but then afterwards it started doing it again.

I also just pulled the vacuum hose off the FPR and there was no fuel leaking out.

 

hmmm, are you running a stock OS? Are you running in SD or MAF, Closed or Open Loop... How old are your O2 sensors? If your Closed Loop do your O2 sensor voltages oscillate evenly and at the same intervals?

 

I'm running a COS-5 operating system setup by Justin. It's using the MAF, and it has the same issues with the MAF plugged in or unplugged.

My o2 sensors, fuel pressure regulator, fuel pump, etc are all stock.

I'll have to check on my tune, but I think it's something mechanical being that the ticking sound occurs even when the truck is moving.

 

did you check the hose on the brake booster?

 

Sure did. I'm running a vacuum mod and it's "T"ed off and running to the transmission. That was actually the first thing I checked. All three connections are clamped on there tight.

EDIT-Oddly enough I just pulled the brake booster hose and it still had vacuum after sitting for 15 minutes! WTF does that mean? I'm still having issues with a mushy brake pedal though.

 

the booster keeps vacuum in case the engine stalls so you can stop the truck with vac. assist