1. Ignition System Problems:
* Worn Distributor Cap and Rotor: These components distribute the high voltage to the spark plugs. Wear or cracks can cause misfires, leading to backfires and rough running, especially when cold. Moisture can exacerbate this.
* Worn or faulty Spark Plugs and Wires: Old or fouled spark plugs won't fire reliably, especially in cold conditions. Cracked or damaged wires can lead to misfires and arcing.
* Ignition Coil: A weak or failing ignition coil won't provide enough voltage to create a strong spark, resulting in misfires.
* Ignition Module (Electronic Ignition Control): This is the "brain" of the ignition system in many GM vehicles of that era. A failing module can cause erratic spark delivery.
2. Fuel System Problems:
* Clogged Fuel Injectors or Carburetor: If you have fuel injection, clogged injectors restrict fuel flow, leading to a lean condition and misfires. With a carburetor, similar issues arise from clogged jets or passages. Cold starts are especially affected because the fuel is thicker.
* Fuel Pump: A weak fuel pump might not deliver enough fuel pressure, especially when the engine is cold and demanding more.
* Fuel Filter: A clogged fuel filter restricts fuel flow, mirroring the effects of clogged injectors or a carburetor.
3. Vacuum Leaks:
* Vacuum Hoses: Cracked or loose vacuum hoses can disrupt the fuel/air mixture, leading to erratic running and backfires.
* Intake Manifold Gasket: A leak in this gasket can cause a similar problem to vacuum hose leaks.
4. Engine Mechanical Issues:
* Worn Engine Components: This is less likely to be the *primary* cause of the shaking, but worn parts (like rings, bearings, etc.) can contribute to rough running and sluggishness, especially when the engine is cold and oil is thicker.
Why it gets better after a few minutes:
The fact it smooths out after a few minutes suggests the problem is exacerbated by cold temperatures. This points to issues that are temperature-dependent, like the ones listed above (thicker fuel, less efficient ignition in cold parts, etc.).
What to do:
This is not a DIY job for the inexperienced. The violent shaking suggests a serious problem that could cause significant damage. Take your Suburban to a qualified mechanic immediately. They can properly diagnose the issue using diagnostic tools and address it safely. Attempting to troubleshoot this complex issue yourself could lead to further engine damage.
Before you take it to the mechanic, try to provide as much detail as possible about the symptoms, when they started, etc. This will help them diagnose the problem more efficiently.
