5.0 TBI cold weather sputtering

Joined
Dec 16, 2009
Messages
106
Location
Rhode Island
Hi everyone,

It seems to be that time of year when my truck runs like crap again. I have a 1995 GMC K1500 5.0L with TBI. All summer long it starts and runs perfect. Once cold weather comes around (temperatures around freezing and below), I start having cold start issues. I crank once for several seconds, and it will start briefly at a low RPM, and then die. Crank again and it fires over, runs decent for 30 seconds or so. Once I put it in gear and let the clutch out, it will start bogging down and sputtering under any load. The idle is also lower than normal. Occasionally it is so bad that the truck will die and restart several times while moving around 10 MPH, jerking back and forth as I hold the gas to the floor to make it stay running. This can be very exciting pulling out into traffic. If I just let it idle for a while before driving, the idle will get slower and slower until it just stalls out. If I 'help' it stay running by feathering the gas and revving the engine several times it will clear up. During this process I get a cloud of steam/white smoke out of the exhaust. This behavior gradually clears up within the first mile from the cold start and it then runs perfect.

I have replaced the coolant temperature sensor (the one the ECU uses to adjust fuel trim, not the temperature gauge sensor) to no avail. I'm not sure what else to check. Either something is wrong, or the TBI system just doesn't atomize fuel well when cold. It seems to run like a 2 stroke that hasn't had enough choke to warm up yet and keep running on its own.

Anyone else deal with this issue on a TBI?
 
Joined
Jul 10, 2011
Messages
645
Location
Martinsburg West Virginia
Without scanning it, my first guess would have been coolant temp sensor (already replaced) since it is temperature related. Did the temp sensor make any difference at all? My second guess would be to check the fuel pressure, the pump may be getting old and weak OR possibly fuel filter. When was the last time the fuel filter was done? In the cold weather they tend to run richer so fuel pressure and flow would be more important in that kind of weather. With the idle being low, I would check all vacuum lines for a leak somewhere including lines going to the brake booster. My next guess would be oxygen sensor but at that point it is truly a guessing game and just throwing parts at it. How fresh are the plugs and wires? Often times just any basic maintenance that has been put off too long is the issue.
 

WA1DH

Thread starter
Joined
Dec 16, 2009
Messages
106
Location
Rhode Island
I actually changed the fuel tank, pump, lines, and filter about a year ago. The oxygen sensor was changed about 5 years ago. I did plugs and wires last year. Distributor cap/rotor were changed when the oxygen sensor was changed. It's always behaved this way in cold weather and I haven't noticed any improvement with these parts replaced. I've just gotten used to revving it out a bit on cold starts and living with it the way it is, but I wouldn't mind fixing it if I could.
 
Joined
Aug 2, 2005
Messages
1,042
Location
dayton oh
clean up that cluster of grounds near the water outlet.
common issue on gm tbi .
the iac can be crudded up too.
or suffering from the bad grounds.
the ecm should keep correct idle via the iac at all times.
and should command high idle that starts dropping as the coolant temp starts to rise.
 
Joined
Jan 17, 2012
Messages
1,832
Location
ventura, ca
clean up that cluster of grounds near the water outlet.
common issue on gm tbi .
the iac can be crudded up too.
or suffering from the bad grounds.
the ecm should keep correct idle via the iac at all times.
and should command high idle that starts dropping as the coolant temp starts to rise.


Good advice. I had the terminals corrode on the grounds and they were not really connected anymore. The idle air is easy to take out and clean and can get pretty nasty with carbon. There are very few vacuum lines but the little 90 degree boots cracked where they attach to the TBI as they got older adding to lousy idle so I replaced all the lines with new hose.
 
Joined
Apr 1, 2020
Messages
1,743
Location
Pacific Northwest
I recently worked on a GM with a fast idle problem where the idle air valve was sticking. I sprayed it out with carb cleaner and gave it a squirt of PB blaster and that "fixed" it, but it came back shortly thereafter. I would try cleaning the AIC valve and if that helps, just replace it.
 
Joined
Aug 28, 2017
Messages
2,539
Location
Cincinnati, USA
I'd clean the throttle body and put some Techron through the injectors... replace injectors if that doesn't help, probably not running rich enough. Minor vac leak could cause that too, and clean off MAF sensor if so equipped.
 
Joined
Oct 19, 2020
Messages
777
Another vote here for checking the engine harness grounds. The old TBI system was reliable as the day is long, but the most recent of systems are 25 years old. They just aren't aging well. Pair that with OBD-I diagnostics, the Rochester fuel injection system and est ignition can be cumbersome to diagnose. 😕 you might also test your new coolant temp sensor to verify it's good. New doesn't necessarily mean its good unfortunately.
 

WA1DH

Thread starter
Joined
Dec 16, 2009
Messages
106
Location
Rhode Island
Thanks for all the tips. I will go through the grounds and check the IAC out first. I know I have seen some green corroded ground straps which could probably use replacing.
 
Joined
Jan 13, 2016
Messages
2,393
Location
Northeast Nebraska
I had a 91 Bronco that started doing this when it started getting cold one year, it would fire right up then die, if I feathered it until it warmed up a bit I could keep it running and then it would idle and run fine. Turned out to be the fuel pressure regulator.
 
Joined
Aug 2, 2005
Messages
1,042
Location
dayton oh
forgot fpr.
the spring rusts when pcv clogs up in the tbi base.
a rebuild kit is cheap.
make sure it has the spring.
oh and clean out the tbi base passages.
usually when the spring goes truck will fall on its face under load or high rpm.
i got one cheap that yoyo'ed cold and stumbled badly.
busted spring.
 
Joined
Oct 20, 2005
Messages
6,989
Location
Scruffy City
Good advice so far.

If you have a capable scanner see if CTS and IAT (if equipped) match actual.

There is a base idle learn procedure, I don’t remember it exactly though...
 
Joined
Jul 1, 2013
Messages
2,428
Location
Ottumwa, Iowa
While it sounds like a fuel issue the ignition system on these did dumb things at times also. The pickup magnets would fall apart in the distributer and the ignition modules liked to die.

My 95 grumbles when starting but eventually smothers out.
 
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