When my engine is cold, it starts poorly, and once it gets fully warm, it idles a bit higher, stops responding to the throttle, produces some black soot from the exhaust, and then stalls. It can only be restarted once it cools down again. My theory is that the temperature sensor for the injection system is faulty. That’* why it runs poorly when cold, and once it’* fully warm, it over-fuels, which explains the black smoke and the inability to restart. The engine has the original injection system. The temperature gauge inside the cabin works and seems accurate. Does the injection system have a separate sensor, and where is it located? Can it be unplugged to test the limp-home mode? I’d really appreciate some help. Greetings from Germany ✌🏼

Moved from General GM Chat to GMC/Chevrolet Truck/SUV .

I think you might be going the right direction.

Is this the 1991 Sierra V3500 in your profile?

Is this the older square body or the newer aero body?

How many miles on it?

Does it get driven often?

Welcome aboard!

Is this the 1991 Sierra V3500 in your profile?
Yes Sir.

Is this the older square body or the newer aero body?
Squarebody!

Does it get driven often?
Actually, not at all yet. I only bought it a few months ago

How many miles on it?

How many miles on it?
122.295 miles
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Do you have a scan tool? Unplug the MAF. Does it do better?
We can look at temp sensors and other things with a scan tool. If no scan tool you'll need to do some electrical tests.