Kyle,
Took a look at the MAP sensor readings today not sure I can really explain what it's doing
I have a new one coming tomorrow and plan on replacing it to see if it helps

Supply Voltage is 5 volts
Engine off key on shows 103kpa
At idle showing 43kpa
while revving the engine Voltage went lower
MAP sensor numbers jumped around quite a bit as hi as approx 100kpa returning to 43kpa at idle Believe it or not the GM service manual actually says compare to another vehicle when diagnosing it Anyway I have a new one coming from Rock auto so I'll see if there is any change I was reading up on possible symptoms and Misfire, rough idle and Sluggish excelleration are some of them, I deffinately have the Misfire and rough idle and do notice that if jumping on it exceleration is kind of sluggish until the intake manifold tuning valve opens up over 3000 rpm so I'll update as soon as i change it hopefully tomorrow
Thanks again

 

Put in a New MAP sensor in today and My Blazer really seems to have woken up!!
Smooth Excelleration Plenty of Power Have lost that sluggish feeling, Idle is a lot better
still some vibration but I think fixing a few exhaust leaks and maybe a new set of Motor Mounts will clear that up. I'm going to monitor it for a few days and see if any Codes pop up
If not thanks for all the input from everyone hopefully some of the info provided will help someone out. Wish me luck

GS

 

Must have missed your post yesterday. Those MAP readings seem to be erratic. Without seeing the scan results (logged data points) and comparing other sensor values to the indicated MAP readings, I cannot tell for sure. But if a new MAP sensor helped remedy the problem, good deal!

 

Just in case the Problem isn't solved any ideas on what else to check?? Here's what I've done so far Rough idle Po301 DTC

1) Fuel system
Fuel pressure test not running 60-62 lbs holds at the pressure
running approx 57lbs
Fuel Filter
02 sensors
Spider, Harness to the Spider and internal lines
2) Ignition,
Plugs, Wires , Cap, Rotor, Distributor,(high voltage ignition switch) check all
visible grounds and cleaned them up
3) Vacuum
replaced all hoses, tested for gasket leaks on Plenum and intake manifold using Carb cleaner and again with some propane gas
4) Sensors
replaced EGR, IAC, Coolant, TPS MAP,Crank sensor
5) checked Cylinder compression all cylinders at 150 lbs checked for a bad valve guide
6) Exhaust
Muffler, and Cat I do have a few leakes in exhaust but they are past the cat

If you have any other suggestions let me know, Truck is running better but in case I have a SES pop up just wondering what else to check

 

Lets cross that bridge when it gets here. I would love to have the time to list off every possibility, but I know I would forget something even if I did have the time.

 

I think we are approaching that bridge, Runs a hell of a lot better but still misfiring slightly.
I did find another vacuum line that runs from the T connection near the Ball on the hood
It runs from there down the firewall to the transmission it is wire tied along with a vent line to the transmission Dipstick tube, so I'm sure it's got to be bad with all that heat . I picked up some 5/32 vacuum line and will replace it tomorrow after work. If not solved I'm going to pick up some new intake manifold gaskets and put them on as well. It's weird only at idle as soon as you even rest your foot on the peddle the mis is gone It's got to be vacuum!!

 

I had that same problem after i replaced my battery, all it ended up being was that it had a bad connection on my positive battery terminal, it was tight but it needed to be cleaned once i did that and put a little electrical grease on the terminal and tightened it up i never had another problem with it.

 

Interesting about the battery, I'll have to take a look at the charging system
I know that when i put the brakes on The voltage meeter drops down but have tested the alternator voltage with everything on and seems to be ok but worth another look at this point I'll try anything

 

Quick Question on O2 sensors, I recently replaced the O2 sensor bank 1 sensor 1 located before the cat converter I was monitoring the O2 sensor readings today the new one seems fine but have noticed that Bank 1 Sensor 2 located after the cat at idle hangs between 700-800mv and once driving seems to function correctly.
My question is would sensor #2 cause problems like the rough idle? From what I understand it monitors the cat. My converter is a few months old so I know it's good.

 

Sounds normal. I never recommend replacing the catalyst monitoring sensors unless you get a code. Only the sensors closest to the engine have any bearing on the actual operation of the engine itself. So B1S1 and B2S1.