2003 SE Engine breaking up at 4100rpm

[tower9447]

I have an issue where the engine breaks up/stumbles at around 4100rpm. The weird part is between 1-2 shift it only stumbles once then keeps accelerating. When shifting between 2-3 it stumbles repeatedly at 4100rm then will finally power through and keep climbing in RPM until shifting from 3-4. I am stumped as other then the issue at 4100rpm it runs amazing. I did the upper and lower intake gaskets, cleaned the throttle body, spark plugs, wires, Ignition control module and coils. Any help would be greatly appreciated.

[harofreak00]

Are you getting actual misfire codes? Pointing at a specific cylinder?

[AJT2004]

Also, did you have the stumbling issue before the maintenance/repairs listed or afterwards?

[tower9447]

I am not getting any codes at all.

I dont really drive the car my girlfriend does and I asked if she had ever had this happen before and she said she has never ran it at wide open throttle like that so she isnt sure. I am assuming the issue could have been there the whole time she has had the car. I was the one who drove it like that after doing all of that work and discovered the issue. Her intake was initially leaking coolant from the throttle body gasket into the intake and after doing some research see that the upper and lower intake manifolds as well as coolant elbows were an issue. So after doing all of that and cleaning a ton of carbon out of the throttle body I found this issue. I know thats probably too much info...ha ha.

I also noticed today that when its really cold out on the first initial start it cut off this morning. It did start on the second try but surged 3-4 times before straightening out and idling.

[95naSTA]

Did you replace the upper intake manifold or just replace its gaskets? If you didn't replace it, did you verify the EGR tube area didn't burn through to the coolant passages?

And when cleaning the throttle body, did you remove the MAF and IAC or use a MAF safe cleaner?

[Sirius]

Also, (this is a reach) what kind of spark plugs are you using, and how old are they? It's been mentioned that our cars don't like platinum plugs so well. Just something else to check.

[tower9447]

Did you replace the upper intake manifold or just replace its gaskets? If you didn't replace it, did you verify the EGR tube area didn't burn through to the coolant passages?

And when cleaning the throttle body, did you remove the MAF and IAC or use a MAF safe cleaner?

I replaced the whole manifold and gaskets. When I cleaned the throttle body I did use throttle body cleaner. I did not remove the MAF or IAC. I did replace those sensors though while I had it apart.

[tower9447]

Also, (this is a reach) what kind of spark plugs are you using, and how old are they? It's been mentioned that our cars don't like platinum plugs so well. Just something else to check.

I am using the recommended AC Delco plugs and Belden wires. I dont remember what plugs. I know they are not platinum. They were installed when I changed the upper and lower intake manifold.

[tower9447]

I am almost ready to tear it all back apart...ha ha.

[tower9447]

Finally figured out what the issue was. The MAF sensor was bad the whole time..Walker brand. During normal acceleration it acted normal but at WOT it went crazy and acted like a rev limiter. Very strange. I replaced it with an OEM style MAF....problem solved. Thank you everyone for the help!

[dougtoth]

The best MAF I found for my Bonneville's is the Hitachi MAF0047.
I buy them from Amazon.
I have never had a problem with this brand.
I believe they make them for GM.

[tower9447]

That is the one that I put in. Turned the car into brand new again.