Motor shakes very bad

multi misfires can be from injectors --dirty and not squirting properly or low fuel pressure ---fuel pump or dirty filters
plugs are only half of a misfiring problem and the injectors are always left out
Next time include all details like make, model , year of car in your question to get a better answer

suggest you check the distributor cap & especially the spark plug wire of the 3rd cylinder

-Sounds like blow head gasket, broken or burn valve.
-Do compression check each cylinder to see what you have and compare to its specification.
Or
-Was it recently rebuild?
If so then timing might be off.
spark plug wire connect to the wrong spark plug.
Vacuum line might connect to the wrong line.
Bad rotor or cap .

Good luck

Mai

For 1999 Buick LeSabre - but you took #1 off the list, so here's the whole "failure to start" list:

Priority Action Part Type Cause
1 Inspect Battery Battery Discharged or Faulty.
2 Inspect Battery Cable Corroded, Broken, Shorted or Poorly Connected Battery Cable.
3 Inspect Distributor Cap Distributor Cap Cracked or Burned.
3 Inspect Fuel Filter Clogged or Dirty Fuel Filter.
5 Inspect Ignition Coil Faulty Ignition Coil.
6 Inspect Wireset Worn, Damaged or Faulty Spark Plug Wire(s).
7 Inspect Spark Plug Incorrectly Gapped or Fouled Spark Plug(s).
8 Inspect Starter Starter Motor Faulty.
9 Inspect Fuel Pump Low Fuel Pressure.
10 Inspect Starter Relay Faulty Starter Starter Relay
11 Inspect Fuel Pump Relay Faulty Fuel Pump Relay.
12 Inspect Fuel Injector Pressure Regulator Faulty Fuel Injector Pressure Regulator.
13 Inspect Ignition Switch Improperly Connected or Faulty Ignition Switch.
14 Inspect Starter Motor Faulty Starter Motor
15 Inspect Fuel Injector Dirty or Worn Fuel Injectors.
16 Inspect Fuel Pump Strainer Clogged or Dirty Fuel Pump Strainer
17 Inspect Engine Control Computer Incorrect Operating Information Being Delivered and Sent From The EEC.
18 Inspect Fuel Tank Fuel Tank Empty.
19 Inspect Carburetor Carburetor Flooded or Faulty Choke.
20 Inspect Distributor Rotor Distributor Rotor broken, burned contacts, or loose
21 Inspect Distributor Worn, Loose, or Incorrectly Installed Distributor.

You already took #1 off the list.
The national auto parts chains (AutoZone, Pep Boys, and Advance Auto Parts) will hook up a
diagnostic tool to your car to perform a Charging System diagnosis for free - its an easy
way to exonerate & differentially diagnose your Alternator/Battery/Voltage Regulator.

Priority Action Part Type Cause
1 Inspect Battery Battery Discharged or Faulty.
2 Inspect Battery Cable Corroded, Broken, Shorted or Poorly Connected Battery Cable.
3 Inspect Fuel Filter Clogged or Dirty Fuel Filter.
4 Inspect Distributor Cap Distributor Cap Cracked or Burned contacts.
5 Inspect Coil - Ignition Faulty Ignition Coil.
6 Inspect Wireset Worn, Damaged or Faulty Spark Plug Wire(s).
7 Inspect Spark Plug Incorrectly Gapped or Fouled Spark Plug(s).
8 Inspect Starter Starter Motor Faulty.
9 Inspect Fuel Pump Low Fuel Pressure.
10 Inspect Solenoid Switch Faulty Starter Solenoid Switch.
11 Inspect Relay - Fuel Pump Faulty Fuel Pump Relay.
12 Inspect Fuel Injector Pressure Regulator Faulty Fuel Injector Pressure Regulator.
13 Inspect Ignition Switch Improperly Connected or Faulty Ignition Switch.
14 Inspect Starter Motor Faulty Starter Motor.
15 Inspect Fuel Injector Dirty or Worn Fuel Injectors.
16 Inspect Fuel Pump Strainer Clogged or Dirty Fuel Pump Strainerat.
17 Inspect Engine Control Computer Incorrect Operating Information Being Delivered and Sent From The ECC.
18 Inspect Fuel Tank Fuel Tank Empty.
19 Inspect Carburetor Carburetor Flooded or Faulty Choke.
20 Inspect Distributor Worn, Loose, or Incorrectly Installed Distributor.
21 Inspect Distributor Rotor Burned Distributor Rotor contact

You've already eliminated the spark plug & wireset, distributor cap & rotor.
Sounds like your car needs a tune-up, specifically, the PCV (positive crankcase ventilation) valve, and/of the EGR (Exhaust Gas Recirculation) valve.

Components checked/replaced during a tune-up are:
air filter
motor oil
motor oil filter
breather filter
fuel filter(s)
fuel strainer
PCV valve
EGR valve
spark plugs
spark plug wires
ECM or distributor cap & rotor
cabin air filter
transmission oil filter
transmission oil
engine coolant
check all vacuum hoses and lines

Troubleshooting the no-start condition - from the 1990 Mitsu Mighty Max Repair Manual:

Priority Action Part Type -- Cause
1 Inspect Battery -- Battery Discharged or Faulty.
2 Inspect Battery Cable -- Corroded, Broken, Shorted or Poorly Connected Battery Cable.
3 Inspect Distributor Cap -- Distributor Cap Cracked or Burned.
3 Inspect Fuel Filter -- Clogged or Dirty Fuel Filter.
5 Inspect Ignition Coil -- Faulty Ignition Coil.
6 Inspect Wireset -- Worn, Damaged or Faulty Spark Plug Wire(s).
7 Inspect Spark Plug -- Incorrectly Gapped or Fouled Spark Plug(s).
8 Inspect Starter -- Starter Motor Faulty.
9 Inspect Fuel Pump -- Low Fuel Pressure.
10 Inspect Solenoid Switch -- Faulty Starter Solenoid Switch.
11 Inspect Fuel Pump Relay -- Faulty Fuel Pump Relay.
12 Inspect Fuel Injector Pressure Regulator -- Faulty Fuel Injector Pressure Regulator.
13 Inspect Ignition Switch -- Improperly Connected or Faulty Ignition Switch.
14 Inspect Starter Drive -- Faulty Starter Drive.
15 Inspect Fuel Injector -- Dirty or Worn Fuel Injectors.
16 Inspect Fuel Pump Strainer -- Clogged or Dirty Fuel Pump Strainerat.
17 Inspect Engine Control Computer -- Incorrect Operating Information Being Delivered and Sent From The EEC.
18 Inspect Fuel Tank -- Fuel Tank Empty.
19 Inspect Carburetor -- Carburetor Flooded or Faulty Choke.
20 Inspect Distributor -- Worn, Loose, or Incorrectly Installed Distributor.

try doing a fuel injector check. do this by pulling each of the cables out one at a time while the car is running. pull out the first one, if the car starts to shake even more, or turn off, then the fuel injector is good. replace the spark plug cable. repeat the steps for the rest. if the car remains does the same thing, as in starts to shake more or turn off, then the problem exists elsewhere. but, if you remove one of the spark plug cables, and the car remains the same, then you found your bad fuel injector. the only other thing that occurs to me is changing the fuel filter. it could be that the fuel filter is clogged, and when you started going up hill, the fuel pump simply couldnt push the fuel up. but the first one sounds more logical. it either sounds like it could be what you said, about one of the cylinders not working, or a loss of pressure somewhere, which would be fuel, or air. usually air is alot less likely to cause problems like this than fuel. hope this helps, goodluck.

1 Inspect Battery -- Battery Discharged or Faulty.
2 Inspect Battery Cable -- Corroded, Broken, Shorted or Poorly Connected Battery Cable.
3 Inspect Distributor Cap -- Distributor Cap Cracked or Burned.
3 Inspect Fuel Filter -- Clogged or Dirty Fuel Filter.
5 Inspect Coil - Ignition -- Faulty Ignition Coil.
6 Inspect Wireset -- Worn, Damaged or Faulty Spark Plug Wire(s).
7 Inspect Spark Plug -- Incorrectly Gapped or Fouled Spark Plug(s).
8 Inspect Starter -- Starter Motor Faulty.
9 Inspect Fuel Pump -- Low Fuel Pressure.
10 Inspect Solenoid Switch -- Faulty Starter Solenoid Switch.
11 Inspect Relay - Fuel Pump ----- Faulty Fuel Pump Relay.
12 Inspect Fuel Injector Pressure Regulator --- Faulty Fuel Injector Pressure Regulator.
13 Inspect Ignition Switch --- Improperly Connected or Faulty Ignition Switch.
14 Inspect Starter Drive --- Faulty Starter Drive.
15 Inspect Fuel Injector --- Dirty or Worn Fuel Injectors.
16 Inspect Fuel Pump Strainer ---- Clogged or Dirty Fuel Pump Strainerat.

shake at idle means u have a cylinder misfire or low commpression, here are causes of misfires most commonly seen.

The most common misfire causes on the cars I've worked on have been:

1. Spark plugs
2. Spark plug wires
3. Ignition coil
4. Fuel injector
5. Wiring to fuel injector
6. Timing Belt
7. Vacuum leak or stuck open EGR
8. Contaminated fuel or bad fuel pump
9. Weak compression
10. Blown head gasket

1 Inspect Battery Battery Discharged or Faulty. 2 Inspect Battery Cable Corroded, Broken, Shorted or Poorly Connected Battery Cable. 3 Inspect Distributor Cap Distributor Cap Cracked or Burned. 3 Inspect Fuel Filter Clogged or Dirty Fuel Filter. 5 Inspect Coil - Ignition Faulty Ignition Coil. 6 Inspect Wireset Worn, Damaged or Faulty Spark Plug Wire(s). 7 Inspect Spark Plug Incorrectly Gapped or Fouled Spark Plug(s). 8 Inspect Starter Starter Motor Faulty. 9 Inspect Fuel Pump Low Fuel Pressure. 10 Inspect Solenoid Switch Faulty Starter Solenoid Switch. 11 Inspect Relay - Fuel Pumpat Faulty Fuel Pump Relay. 12 Inspect Fuel Injector Pressure Regulator Faulty Fuel Injector Pressure Regulator. 13 Inspect Ignition Switch Improperly Connected or Faulty Ignition Switch. 14 Inspect Starter Drive Faulty Starter Drive. 15 Inspect Fuel Injector Dirty or Worn Fuel Injectors. 16 Inspect Fuel Pump Strainer Clogged or Dirty Fuel Pump Strainerat. 17 Inspect Engine Control Computer Incorrect Operating Information Being Delivered and Sent From The EEC. 18 Inspect Fuel Tank Fuel Tank Empty. 19 Inspect Carburetor Carburetor Flooded or Faulty Choke. 20 Inspect Distributor Worn, Loose, or Incorrectly Installed Distributor.