I have 3 GMT400s ,all running, and a few for parts. There's always things braking, because of age. Some Are- Distributor and disturber inner parts failure, no spark.
MAF sensor, never had much trouble with them, but sometimes...
IAC valve and IAC connector, too much air or none, Injectors ,have had some TBIs with bad gaskets and plugged injectors, injectors not firing or spray patter all-over-the-place, I have had good results using a hydro sonic cleaner
And thee best one is that electrical ignition switch down on the steering column, sometime it will still power up everything when key is off and out off ignition. Some times it will start and not start because the inside of the switch is worn out ,can cause some grief, intermitting voltage to areas it shouldn't and vise versa I just got 3 in from Rock Auto.
The one on my dually wouldn't shut off, even when I disconnected the battery, had to cut the power wire to the alternator to shut it down.
I would go at it, like I'm steeling it, hot wire , then reverse engineer (troubleshoot) it.
MAF sensor, never had much trouble with them, but sometimes...
IAC valve and IAC connector, too much air or none, Injectors ,have had some TBIs with bad gaskets and plugged injectors, injectors not firing or spray patter all-over-the-place, I have had good results using a hydro sonic cleaner
And thee best one is that electrical ignition switch down on the steering column, sometime it will still power up everything when key is off and out off ignition. Some times it will start and not start because the inside of the switch is worn out ,can cause some grief, intermitting voltage to areas it shouldn't and vise versa I just got 3 in from Rock Auto.
The one on my dually wouldn't shut off, even when I disconnected the battery, had to cut the power wire to the alternator to shut it down.
I would go at it, like I'm steeling it, hot wire , then reverse engineer (troubleshoot) it.