RPM dip when lightly pressing accelerator at idle

[RyanTBZ]

Hey Guys

I am having an issue with my 03 Trailblazer. When the truck is idling and i give it some light gas the RPM's drop and the engine feels like it hesitates and then sort of stumbles when the RPMs dip. Then the RPMs go up and drop back down to normal idle. I replaced the spark plugs since they were the originals from the factory with new AC Delco Iridiums 41-103 in an attempt to fix the problem, but there was no change. I also recently changed my ignition switch since it was going bad. Recently removed and thoroughly cleaned the throttle body as well and pulled the PCM fuses after to allow it to reset.

I made a video of what is happening when I give it light gas when idling. It seems off to me, but maybe this is normal for these trucks?

http://youtu.be/ZK_erTvLBCg

I'm thinking maybe I should swap out the fuel filter next since that looks original as well and needs to be changed either way.
Thanks in advance for any advice.

 

[kickass audio]

Mine does that sometimes too. I wouldn't be concerned about it. I noticed if I keep the truck in gear it never happens but if its in park like you said mine does that once in a great while.

 

[RyanTBZ]

Mine does that sometimes too. I wouldn't be concerned about it. I noticed if I keep the truck in gear it never happens but if its in park like you said mine does that once in a great while.

I noticed that as well. In Drive it will never do the RPM dip. I held the brake while in drive and gave it light gas a few times and there was no hesistation/drop at all.

It is strange.

 

[The_Roadie]

Ever changed your CPAS?

 

[RyanTBZ]

Ever changed your CPAS?

Nope I never changed it.
Should I clean it or replace it? It seems that a new genuine GM one can be had for a little more than $40 which isn't too bad.

 

[kickass audio]

I will admit I have changed mine and it still does it once in awhile but only in park. I don't think its that Bill.

 

[gmcman]

I would start with the fuel. Whether it's the filter, verifying pressure, checking the FPR (fuel pressure regulator) for leaks. To visualize the point I'm making is, when you step on the gas, especially from idle, you instantly increase the compression. Not so much the compression ratio, but you go from a very sparse amount of air to a dense amount and needs fuel right away. Perhaps the fuel can't keep up right off the bat and this could be from dirty injectors, restricted fuel filter, low fuel pressure and this could point to a filter....I would change it first to be sure.

Could be other factors for sure but this is where I would start.

 

[SmokeyMcBlazer]

Mine does this once in a long while too. I have had it happen while in drive once.

 

[KNBlazer]

Mine does it too and has done it since I can remember... 2004 TB 4.2, bought in 2005, recently rebuilt engine still has this nuiscance, I think it might be computer related.... maybe someone who has a tune can verify this possibility...

 

[Sparky]

Mine tends to do that also. Plugs, CPAS, clean TB, new fuel filter. Cleaning the TB made the most difference but still does it. I pretty much ignore it now. Only really does it when in park and I tap the gas, so whatever.

 

[RyanTBZ]

Changed out the fuel filter. Seems to have improved a little since it doesn't vibrate as badly when the RPMs dip.
I'm going to get a fuel pressure gauge and see if I can find anything. Try to rule out the cheaper stuff first and then move up the list instead of just throwing parts at it.

 

[BVEN]

My RPM's dip as well with the same symptoms. I've been chasing this for a while now (years) and hope to resolve this issue quick, fast and in a hurry. I am about to replace the VVT solenoid and hope it solves any of my problems; -6 LTFT (no codes), knock, hesitations, rpm dip when tap. After the VVT solenoid I will hit up the forum again to search for the fuel pressure test ports to see if the FPR needs to be swapped.
If anyone has any suggestions, just to save time, this is what I've done

O2 sensors
Fuel Filter
Spark Plugs
Belt
Belt tensioner

Thanks ahead of time for anyone throwing me a bone

 

[joe mama]

Clean the throttle body first. A can of cleaner costs less than $5, and does wonders for these types of issues.