1995 chevy blazer 4.3 vortex 2 wheel drive 2 door, My problem is the truck has started to run rough (idle fast) and it will increase speed on its own at times. It also will miss at times and every light goes on the dash board when it does this. I thought it may be a vacume leak but all the hoses seem okay, and if this makes any sense it seems to run better if i have at least 3/4 of a tank but it still acts up but not as bad

1989 Chevy blazer 4.3 won't start..I have ... - CarGurus

www.cargurus.com > Questions > Chevrolet > BlazerCarGurusJan 30, 2013 - 96 Chevy S10 Blazer with 4.3 L engine vortex will turn over but won'tstart. ... i a 93 k5 blazer 5.7tbi in cold weather it will not start, if i hook jumper ... was told it just needed a Fuel pump, I replaced the Fuel pump, and the Filter, ...

Normal cranking pressure is 70psi. It won't start if pressure is below 60psi.
Engines with multi port injection runs on 35-40 psi. and engines with throttle body injection run on 25 psi.

If you mean the control module, previously called the "computer chip" it is under the distributor cap. If you mean the fuse box it is under the dash on the drivers side.

my guess, car unseen.
car has an A/T trans, and all A/T jump from park to drive
selection is made on a cold engine, due to the very fast idle speed.
what was the park and cold idle speed. and out door temps.
the lower out door temps, make idle speed , cold engine, even higher
but when the engine reaches 180F or more and holds, the RPM
is about 800 RPM (the FSM tells the exact amount and does vary for the unstated engine option) so at 800 the tranny don;t lurch, did it on a hot engine. so if idle speeds are wrong say so and say it with engine temps. or its all meaningless.
next :
runs rough, the engine (even parked?) is called misfire.
misfire on a good engine (full compression)
is:
1: bad spark (or never had a tune up ever) every 60k miles.
2: bad fueling. too rich, too lean (low idle) bad injectors (stuck or clogged, or wrong fuel pump pressure or bad Fuel pressure regulator)
3: bad fuel.

there is a test for each possible failure. all very simple test.
it takes $80 in gauge tools to find engine problems.

Yes, but also could be some oil pressure sensor go to bad, if the ECU sense this problem, will turn off the engine.

do you know the codes ? have you checked the oil level?

possible vacuum leak

All GM have ignition coil problems , your getting too much fuel , I have seen O2 sensors and plugged catalytic mufflers too many times , be careful the next ride the vehicle will catch on fire..Try the coil first

idle speed control sensor is what they call it

I now these trucks pretty well, I own 2, a 2000 two door and a 95 4 door and before them I owned a 88 and an 87, so look I suggest you use 4 hi but in low geer(1st geer) and just let it grab by itself, cause I find first thing it's hard getting into 4 low cause you must be in neutral,and I usually engage it with only the ignition on without actually running the truck to make sure it actually engages, we get a lot of snow up here so I'm letting experience speak for itself, hope it helps...

goodluck...