Lack of acceleration / hesitation

[greentahoe]

Recently I picked up a 2003 Trailblazer EXT LT 140,000 miles and a brand new GM transmission. Right from the first day I noticed that when I would tap the gas after the truck was at a warm idol (Aprox 600RPM's ) the engine will almost stall for half a second before reving up. I've also noticed that if I roll up to a stop and don't slow all the way down before getting back on the throttle the truck doesn't seem to down shift unless I almost put it to the floor.

Here is some background:

No codes have registered. I've replaced the catalytic converter and downstream o2 sensor (due to not being able to remove the old one). I've also replaced the spark plugs with OEM delco. When replacing the plugs I noticed that the valve cover is leaking around the plug wells. I plan on replacing this soon. I've also noticed a leak or crack at the exhaust manifold.

I'd like to figure out what this issue is. Any help is appreciated.

 

[The_Roadie]

Welcome! Glad you found us. I would check the data coming out of the upstream O2 sensor to see if it's gotten old and sluggish. And definitely remove and clean the backside of the throttle body with the battery disconnected. It may relearn better behavior.

You used Delco 41-103 iridiums?

Next, check long term and short term fuel trims to see if you have a vacuum leak. Compression while you're at it if you have the tools.

Fuel pressure regulator may be flaky or leaking, which affects fuel flow when you give it the gas.

Also, if it's new to you with an unknown maintenance history, EVERY FLUID is due to be changed at 100K. Especially the transfer case which should have been serviced every 50K, not the usual 100K. Many new owners don't get this detail from reading the Owner's Manual.

 

[greentahoe]

Yes, AC Delco 41-103.

What kind of data should I be looking for from the sensor?

I noticed the spark advance goes negative when the stutter happens.

 

[greentahoe]

Here is what I got for live data:

These are where where I noticed a odd vibration / hesitation:

 

[TobyP]

Here is what I got for live data:

These are where where I noticed a odd vibration / hesitation:

I know this is a super old thread, but did you ever find out what was going on or find a fix?

 

[Mooseman]

The OP has not logged on since 2014 so I doubt very much we'll hear anything.