Thread: 4th gear stumble

So I think the stumble in my RPM's is only happening when the car is in fourth gear.
The RPM's will fluctuate up and down a bit. But if I give it RPM and more gas it runs fine under boost.
From a dead stop it's fine also.
Driving in today I put it in 3rd gear for a bit on the highway where I notice it the most with little gas and rpm there was no fluctuating of the RPM's. Flip it back into forth and it starts again. It's not constant but happens every minute or less.
I replaced most all of my vacuum lines with silicone lines.
1999 GTP - running taylor wires, 605 plugs, short ram with open cone.
Any thoughts?
The codes I keep getting and haven't been able to figure out are
P0452
P0440

Please google your codes and write the names in your post. Once you do that, you'll understand part of the reason why you have a stumble.

You have a vacuum leak.

The P0452 is for fuel tank pressure sensor circuit low voltage.
The P0440 is for the EVAP system.

I haven't been able to figure out the P0440. That was the code I had when I got the car. I thought I fixed it when I found that the previous owner didn't install the o-ring onto the sending unit when he fixed and or replaced the fuel pump.
After I put the O-ring on the code cleared and I thought all was well.

I still had the stumble at this point.

A week after my o-ring fix these two codes came up.

Gearchatter.com is a great FSM code resource

here is P0440 for your reading.
GearChatter.com :: View topic - DTC P0440

Thanks Bill.

I read one similar to that on a different site. I don't have access to a smoke machine so I may have to take it some where after all..

Or find alternatives.

You don't have a smoke machine, so you spray TB cleaner on the connection points and if you get a change in idle... spray that area again.

Most of us don't have all the best tools and coolest ways to check things, we might have alternatives though. And those can work just as well.

Bill -

I have tried the TB cleaner in the engine compartment with no idle changes. So I will try that around the fuel system out back.
Thanks for the tips I appreciate it.