Hello forum goers! Ive been having a weird issue that I can't really attribute to anything... I have an 03 LS (3.4L) with 101k, stock for the most part. When I cruise at lower speeds and am hardly touching the throttle, so say 1500-2000 rpm cruising between 30 and 50, the engine has a weird hesitation. It stays in gear and the car doesn't lose speed, but I feel as if the power drops by about 10-15% for half a second, and repeats in a juttering-like fasion on and off for 3 or 4 seconds. All the while the pedal not moving anyway differently. It makes no weird noise, the transmission got all new fluid and a flush at 75k and shifts crisply and quickly, all new engine gaskets 7k ago, and when I punch it i have full power with no hesitation anywhere. Oil every 3k, coolant every 2 years, new water pump, serpentine belt, air filter, and overall runs perfect. Is there something leaking or clogged that would have these symptoms, or could this be very early signs of transmission slippage? I've been meticulous with maintenance since about 62k when I got it, and I noticed it start to happen around 90k... any insight is appreciated. And sorry for the essay- I just wanted to give the whole story.

 

A good starting point would be plugs and wire and a fuel filter, if it still happens I'd test your injectors and fuel pump

 

Could also be the start of a failing sensor. I believe when you are WOT the O2 sensors just open and don't make changes. Could also be a MAF sensor beginning to fail.

 

My experience with symptoms like that on the 3100 has been ignition system related. Either plugs in need of replacing, an arcing wire or rare (but has happened) a bad coil pack.
At that mileage (100,000), you are due for a few things if they were not done already:
- Trans fluid and filter change (has nothing to do with your current problem, but good maintenance).
- Air and Fuel Filters (you mentioned the air filter was done, change the fuel filter too).
- Plugs and Wires (plugs are rated in modern GMs to go about 100,000-150,000 miles)
- O2 sensor (specifically the upstream one, about 70,000 miles).
- Cleaning the MAF with a can of MAF cleaner (following instructions on the can) is a good idea

With the Plugs, STAY AC DELCO or NGK (stay AWAY from Bosch). Bosch wires are fine, AC Delco better. O2 sensors, stick with AC Delco (prefered) or Delphi.

The 3100 (which the 3400 is based on) is also known for gunk building up in the tunnel connecting the EGR to the UIM (but your symptoms do not sound like that). My best guess is the issue is contained within the plus/wires/coils.
Here's a link from the Bonneville guys on how to test the coils (I have not done this yet myself, but I will next time I think I have a coil problem):
View topic - Comprehensive guide for troubleshooting Ignition coils : PontiacBonnevilleClub.com

 

Alright, thanks guys. Looks like I got some trouble shooting to do (always fun). I'll clean the MAF, look into new plug wires, and also a new fuel filter to start. The plugs and trans fluid are new, but thanks for the heads up. I'll say if any of these other items helps the issue.