The other day I came to a stop sign and my blazer died on me, I smelled gas and noticed white smoke coming from the exhaust, I had to use both pedals when coming to a stop sign to make it to the house, I replaced the spark plugs and spark plug wires which stopped it from cutting off but still idles bad and misfires, I had a buddy read the code for the erg valve so I replaced that and the gasket it’s having the same symptoms, any advice?

 

Did it overheat at some point before the trouble started?

Is it still smoking white from the exhaust?
If yes it could be an indication for a head gasket leaking coolant into one or more cylinders.
This can also cause misfire.

As diagnostics the following comes to mind:

Check radiator with cap removed (cold!) for bubbles or use an appropriate exhaust gas tester on the coolant.
Compression check.
Radiator leakdown test (pressurised and vacuum)

 

So I took it to my mechanic and he read a code for the cam shaft sensor and took a look The distributor cap, he then replaced both The car is running a bit better but still more or less the same symptoms, he recommended replacing the catalytic converter because he read another code for an o2 sensor and believes it’s clogged, any advice before I replace that. (Also not blowing out white smoke anymore) also mentioned something about a vacuum leak on my break booster

 

o.k. so it takes another direction. A vacuum leak can cause bad running and misfire, especially at idle. Vacuum lines are definitively a possible problem source. A leaking brake booster is also a vacuum leak.

 

Where should I start when diagnosing a vacuum leak?

 

I start at the source which is the intake manifold. Several ports usually plug into the manifold. Vacuum is in most instances small diameter hoses (10 mm / 3/8" O.D.) with thick walls so relatively small inside diameter. This for the hose not to collapse under suction. A bigger port is for the brake booster.

Vacuum is used throughout the Blazers. It goes even inside for the A/C controls. A service manual is a great help as it contains schematics for the vacuum system. Most can be diagnosed with running engine (careful about the moving parts on the front - fan, belts, etc.) Listening for the hissing sound a vacuum leak makes. An alternative is to use a vacuum pump and pull a slight vacuum onto the various lines.

A first step may be to check all the lines visually and by feel or unplug them and check one section by one with the engine off. Careful as the connectors are plastic and become brittle. Check for chafing, braking, rubber that gets old and cracks, broken connectors, broken plastic parts etc.