Truck Stuttering while Cold, Runs fine when Warm

[twiget]

So here is the deal, I got into my 'burban this morning to go to work, and it started up same as always. But when I gave it some gas, it would surge-bog-surge-bog until it finally smoothed out after about 10-15 seconds. The check engine light never came on.

I got about a mile from home and decided to turn around and drive my Toyota to work. Just as I'm turning down the street I live on, it is like someone flipped a switch and the surging went away, and the truck was perfectly drivable (still drove the Toyota to work) which is why I thought there might be a choke issue.

It is a '90 with a TBI 454, is there even an adjustment for the choke on it? I have had a couple EGR valve codes pop up in the last few weeks, but nothing today.

 

[4X4HIGH]

TBI does NOT use a "choke". This is all computer controlled stuff. If you have an EGR code then you need to fix that which is probably your issue anyways.

 

[twiget]

Ok, so choke is the wrong term, but the concept is the same, the computer is dumping extra fuel into the intake so that enough of the cold fuel will atomize and mix with the air to burn.

The question still remains, any thoughts on what I should check/adjust/look into? I'm not convinced that the EGR valve is the culprit (though it is towards the top of my list of things to fix), since the valve only comes into play when the engine is warmed up. If the EGR valve was stuck open, the computer should be throwing a code, and I've not had any codes pop up while this was happening.

I went for a test drive this evening, and it did the exact same thing, horrible performance and has a hard time idling while it was warming up, but once it warmed up it ran great.

 

[vortec]

check your IAC (idle air control). it's a cylinder sticking out of the passenger side of the throttle body assembly. it basically opens and closes a bypass circuit in the tb for when the throttle plates are closed. if you can't move the little shaft in and out with light finger pressure then it may need to be replaced. i had to pull mine and clean it off once but other than that it has been fine.

 

[79rustyk10]

I would tend to think that with it running like **** cold then fine warm, maybe it could be the coolant temp sensor. I wouldnt think that EGR would could cause that, isnt it mainly used while at cruizing speeds on the highway?

 

[496truck]

It's not the IAC or CTS (coolant temp sensor). I've replaced both with the same problem still existing. As soon as it's up to temp it's like a switch gets turned on and it runs perfect, similar set up on my 350TBI. I've also replaced the O2 sensor on mine cause the wire was broken and no change. I'm betting on it being an EGR problem. Was gonna pull the EGR and make a block off plate for it but haven't gotten around to it, it's been a year now. I've just been letting it warm up a bit before driving it.

Oh, and I've already gone through all the vacuum leaks and fixed all that. No change.

 

[GalDemSuga]

I only recently played this game with my truck and it was that blastedEGR I'd log using WINALDL just to be sure the the coolant temp switch is working too. But listen to 4x4High and me that EGR is a SOB.

Ok, so choke is the wrong term, but the concept is the same, the computer is dumping extra fuel into the intake so that enough of the cold fuel will atomize and mix with the air to burn.

The question still remains, any thoughts on what I should check/adjust/look into? I'm not convinced that the EGR valve is the culprit (though it is towards the top of my list of things to fix), since the valve only comes into play when the engine is warmed up. If the EGR valve was stuck open, the computer should be throwing a code, and I've not had any codes pop up while this was happening.

I went for a test drive this evening, and it did the exact same thing, horrible performance and has a hard time idling while it was warming up, but once it warmed up it ran great.

 

[twiget]

I wouldnt think that EGR would could cause that, isnt it mainly used while at cruizing speeds on the highway?

That was my understanding of the EGR system too, but what do I know?

I'll check the IAC and CTS just to be sure, and as I mentioned above, the EGR is towards the top of my list of things to fix. Guess I'm moving it to the top.

With Halloween being this weekend, it will be Sunday before I can work on this. Thanks for the info guys.

 

[Camaro Chris]

Every time I have had this problem, it was spark plugs. Try some sea foam down the intake or pull some pugs and check the gap; cheaper then chasing sensors. hope it helps

 

[Keitha]

It runs well when warm because the computer enters Closed Loop mode and self corrects for a rich or lean condition. Closed loop does not solve the problem, it just corrects the symptoms of the problem - you still need to fix it.
Do you have a laptop to scan the data flow? You can then monitor what all your sensors are doing and help issolate the issue.
How is your fuel pressure and fuel filter?

 

[twiget]

Forgot all about this thread.

I dont know what changed, but the truck is running fine now. Starts right up in the morning, idles fine when cold, no stuttering at all when I drive it. I didnt do anything other than drive it.

If the issue comes back, I know what to look for now.

 

[diesel4me]

Probably water in the fuel....this time of year gas stations run their tanks near empty to make room for the winter blend of gas,and your chances of picking up some water greatly increases...some engines run weird on the winter blend of gas if the temps stayt "warm" too..