Cold start issues

[Daniel5121]

Hey guys I wondered if anybody in here has some input on a mechanical reason for my 02 5.3l not wanting to idle on it's own without help for 30-40 seconds when it's a cold start. The reason I'm askink what could be causing this mechanically is because I've had my computer tweaked 3 times the latest time by Nelson and every time the problem remains. It's the only thing keeping my truck from being mechanically perfect. Thanks in advance for any input

[RedHeartbeat]

too rich?

[Daniel5121]

That was one thing I was suspecting with my old tune, the guy was a jerk and didn't want to tell me anything he did and I thought it was tune related that's one thing that prompted me to seek a reputable tuner and what led me to Nelson performance now that I have my new computer the problem is still there. The truck runs great everything is new with exception of the o2s. It's more of an annoyance right now.

[RedHeartbeat]

a wideband will help a ton in your feedback with Allen. Put one in and then monitor the AFR at startup so he can tweak it. You could be lean or rich, either way can cause idle issues. Is your truck stock? Can you pull the PN off the fuel injectors so Allen will know exactly which ones you have in the truck? Are they the stock injectors?

[Tarinitup1]

Tuning can't fix everything. Try cleaning your throttle body's iac.

[Daniel5121]

Yeah it's an all stock 02 5.3 withe the exception of a fabed intake box, thorley long tubes, and dual exhaust. No motor mods. I will clean the maf real good this weekend. One thing, my o2 sensors where ones I was running with my previous motor which was a lt1 that overheated and I cracked on of the heads. Think those might be bad?

[DSCZ71]

Your o2 sensors should not be the problem since the PCM does not read them on cold starts.

Edit: I got to thinking about it... on a cold start the truck runs in open loop (no feedback from o2s) until the coolant reaches a certain temp, at which point it will go into closed loop. The reason it runs in open loop until the truck warms up is becuase a cold engine needs a richer fuel mixture (thats why carb motors have chokes) and the o2 sensors need time to warm up.

So im going to go out on a limb and say your coolant temperature sensor is bad! If the coolant temperature sensor is indicating that the coolant is warm enough for standard closed loop operation when it is really not, then the cold engine is not going to be getting enough fuel and the o2 sensors will not be warm enough to provide accurate feedback. Back to the carb analogy, if you start a cold carb motor without the choke it would not idle and you would have to give it some throttle to keep it running until it warmed up.

[Oldspimp]

Sounds like your fuel pressure reg. is leaking down

[pedro mendoza]

Had the same problem on my 01 silverado and turned out to be intake manifold gasket. Replaced it and problem was no longer an issue

[George C]

if the vehicle is mechanically fine then the tables need tweaked for cold starts.