Strange Hesistation and Cutting out
 

This is the problem with the Blazer. At idle its perfect, then if you put it in drive and let it run for a moment like at a traffic light it will try to die. It will shake and then the idle will straighten itself out. When you take off it has an off idle stumble. Then it takes off with no problem. Then it shifts with no problems. It will not do this cold, only after its warm.

Then the other problem it has is when your going up hills, when the engine is under a heavy load at 1500-1800/55 MPH just before it downshifts down it will jerk like the engine is missing. I saw in an earlier post about the trans shudder.. I will pick up some of this stuff and see if it works.

I'm not sure if these 2 problems are related.

I have replaced all 4 O2's, Plugs, wires, rotor and cap. I have cleaned the MAS. Still no better. It's not throwing any codes.

Anyone got any ideas??? Until I can get a decent scanner I'm out of ideas.

Over 65 MPH it doesn't seem to do it at all.

When was the last time a full tune up was done? Why did you replace the O2 sensors??

Kyle a full tuneup was done last fall. It didn't help a bit. I replaced the O2's as they are 14 yrs old. I realize now it was probably not needed, so now I have 4 spares. Whats weird is when it's in cold mode there is no hesitation in the engine. If you blip the throttle it picks up perfectly. But when its warm it will bog out for about 1/2 a second when you rev it. If your at a stop light and baby it off the line it's not that noticeable, but it you floor it it will fall on its face then once it gets to about 1000 rpm it clears up. I'm at a loss trying to figure it out. It has about 18" of vacuum at idle so I don't thinks its a vacuum leak. All the hoses look to be in good shape. Any and all suggestions are welcome at this point.

The fuel filter was replaced last summer because it was pretty much stopped up, the fuel pump was replaced with a Delco unit last fall. Now my fuel gauge reads correctly and its a lot quieter too.

EGR valve nice and clean?

If you remove the pre-cat O2 sensor and drive it around, does it still bog out?

EGR Valve was cleaned a couple of months ago. The cat was replaced last summer as the old one was broken inside.