So I bought this 2004 blazer a few months ago and I think the map sensor is going bad. Honestly idk I just need a second opinion. The check engine light will come on and off, the last time I got it checked it said it was running lean. So I replaced o2 sensors, which definitely helped, but not what I was looking for. When I go to start the truck it値l turn over for a while and then just come to life. (I have to give it gas/ no weird sounds) Then every once in a while I値l be sitting at an intersection and give it gas, and it値l just bog, and bog until it picks back up and launches down the road.

 

What codes were you getting when it was "running lean"? Have they cleared now?

Any other codes?

Why do you think that the MAP sensor is bad?

Do you have a code reader with live data capability?

George

 

If I had to guess, it sounds like you have a fuel pump/delivery issue. They make the truck take long to start and run "weird" when they start to go out. Of course they can go differently but.. one day, when it goes out completely, it won't start back up until changed.

Edit: My truck stalled at lights too, turns out I did in fact have a vacuum leak. It was obvious to everyone, except for me. Spent some time tracking down a part then installing the part (would take a normal person about 5 minutes, with part to be replaced. Took me about two months with much drama) and now it acts as it should. And I STILL don't have a PERFECT (brand new orange) seal on it. But it still runs 98% perfect.

 

I traced a possible fuel.pump.issue by the stumbling and rouhh running symptoms and found no issues. Then looked at plugs replaced those and lost all power to start. Cleaned dist cap contacts and would not even fire st all. Finally just replaced the dist cap. Runs great now.

 

There are many possible causes to your problem. I'm trying to help you narrow down the possibilities by seeing if we have any other clues to start with and then to get more information if we can which might help us take a targeted approach.

Some possibilities:
Fuel system (injectors, regulator, filter, pump)
Bad fuel
Weak ignition (ICM, coil, wires, rotor, cap, plugs)
TPS
Vacuum leak
MAF
EGR
Cat
O2 sensors
MAP
ECT
...

As you can see the list is pretty long so throwing parts at the problem without a diagnosis can get frustrating and expensive.

Besides the code history, a scanner with live data can help us get focused. Example: watch the TPS output while moving through the range at KEEO to see if the output is smooth or erratic. Other examples are ECT, MAP and MAF values or fuel trims at different rpms.

If you don't have that capability or don't want to go that route then start with some lower tech analysis:

Fuel pressure sticky
Look for 1" of strong blue spark at the plug ends of the wires
Look for arching in the dark while spraying water around the ignition components
Spray water around vacuum leak areas to see if idle rpm changes, inspect vacuum hoses
Disconnect the MAF and see if it runs better
Tap the cat and see if it sounds crunchy
Clean the EGR if you have one
Does it run better cold?

If I can help you analyze your problem I will. If you prefer the parts cannon approach, there are many here that can give you ideas.

George