99 tahoe doesn't like the cold

[kidafrika2020]

I have a 99 Tahoe and I live in Anchorage AK. When the temp gets down to 30-40 degrees, my tahoe starts to run rough. If I press the gas pedal down 1/4 to 1/2 the engine sputters and dies. When the temp gets below 10 degrees, I just have to barely tap the pedal and it sputters and dies. It does it when in gear or in neutral. I am thinking MAF Sensor but that is an expensive gamble.

 

[1999HOE]

when its warm or just when shes starting up?

 

[kidafrika2020]

If I let it warm up it will run a little better, but it still does the sputter and die.

 

[95TwinTT]

I have a 99 Tahoe and I live in Anchorage AK. When the temp gets down to 30-40 degrees, my tahoe starts to run rough. If I press the gas pedal down 1/4 to 1/2 the engine sputters and dies. When the temp gets below 10 degrees, I just have to barely tap the pedal and it sputters and dies. It does it when in gear or in neutral. I am thinking MAF Sensor but that is an expensive gamble.

It sounds more like the MAT sensor. (Manifold Air Temp) The ECM watches the incoming air temp and changes the fuel mixture to match. The MAT sensor looks like a water temp sensor from the outside. I don't know the exact location, but it would be right around the throttle plates, screwed into a air duct.

It could also be called the IAT sensor on your truck, (Intake Air Temp) and could be clipped to the air duct.

There is a chance that they changed the style of sensor on your year, I don't know. It should be easy to spot.

The MAF I suppose could be the problem, but I would chase the temp sensor first, they are cheaper. :yesnod:

You didn't mention the conditions of the engine itself. Does this happen whether the engine is cold or hot? There are seperate parts of the ECM program that add fuel to a cold engine, seperate from the air temp. It watches the coolant temp. :cool2:


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[kidafrika2020]

Like I said in a previous post, if I let it warm up it will run a little better. But if I try to give it to much gas, sputter and die. It also smells like the engine is running really rich.

 

[95TwinTT]

Are we talking coming off of an idle while sitting still, or does it happen at any speed, when you hit the throttle?

If coming off an idle, the ECM will often switch from open loop, to closed loop and start paying attention to the O2 sensors.

In open loop, the parameters are controlled by only the progamming, when in closed loop, the O2's are given the authroity to over ride the program and make changes.

The other input's that also influence the mixture are the TPS, MAP, AIT, MAT, MAF and coolant sensors. Any of these sensors acting up can cause problems. You can test some of these sensors yourself with a meter.

The best thing you could do would be to get to a scanner that can check all of these sensors in real time while running. It may cost a few bucks to scan it, but it will probably be cheaper than firing the "parts cannon" at your Hoe.

I just replaced one of my O2 sensors yesterday that was causing my A/F to go extremely rich in closed loop. It was easy to spot, because I have a mixture meter in the dash.

Good luck chasing it down........

 

[kidafrika2020]

I changed the AIT already and no change.

 

[95TwinTT]

I would get to a shop grade OBD2 scanner and check out the individual sensors while the truck is running.

If you can duplicate the problem over and over, you should be able to catch the problem sensor or find the variable that is messing up.

Oh, and it helps to have someone familiar with the scanner to quickly get to the desired readings.