Loss of RPMs at speed continues

[uberninja]

I'm still working through this issue, I thought i had the issue resolved with the transmission not kicking down but now its returned to its old ways. I can put my foot down about halfway up past 45 in over drive, but then it kicks down from 3k rpm to 1800rpm and stays there until WOT where it will downshift to 4k instead of the 2800 or so it usually does when you apply more gas. The weird part is that while cruising at lower speeds, I can give it gas and the rpms jump for a half second and then drop back down with no noticeable increase in speed. I've noticed in recent weeks that if I listen carefully as I apply gas (1500-2000 rpm), there seems to be a weird suction-esque sound, but I can't tell if its at the front or in the back. It also surges slightly at idle. It seems to go up 75-50 rpms every couple of seconds and is audible.

What I've done so far:
I checked the codes, and am not getting anything other than 3-4 shift issue.
I checked the throttle body and cleaned it.
Air filter and MAF has been replaced. (Had an issue last summer where I wouldn't get any throttle unless WOT and this replacement MAF helped, possibly dead after 6months?)
Fuel filter has been replaced.


My question is, where do I go from here and what do you guys think? I was thinking about having the fuel pressure checked to see if that might be the issue,. Maybe a bad fuel pressure regulator or a vaccum leak? I know my fuel pump squeaks a little bit, but it has always done that, even when it was running fine. If it matters I've been running BP 89 lately.

She's becoming my second car today, but my primary winter vehicle and would love to sort this out ASAP. Thanks!

 

[trashtruck]

sounds like an air leak some where.have you checked vacuum lines, intake, sensor gaskets?

 

[uberninja]

sounds like an air leak some where.have you checked vacuum lines, intake, sensor gaskets?

From what I could see things looked ok, but I would have to spend more time underneath to get a better idea. The intake seats well and is on tight. Which sensor gasket do you have in mind?

 

[trashtruck]

i was thinking air intake valve gasket or throttle body gasket.

 

[uberninja]

i was thinking air intake valve gasket or throttle body gasket.

So I went ahead and replaced the IAC and gasket, it was fairly dirty on the inside. I cleaned out the intake as best as I could. Unhooked the battery for 15min and then reconnected everything and ran it for 15minutes. Idle is a lot more stable now. But I still seem to be getting that noise from underneath. Its just weird that its really only noticeable around 1700rpm. Guess I'll keep digging around.

 

[uberninja]

So I went ahead and replaced the IAC and gasket, it was fairly dirty on the inside. I cleaned out the intake as best as I could. Unhooked the battery for 15min and then reconnected everything and ran it for 15minutes. Idle is a lot more stable now. But I still seem to be getting that noise from underneath. Its just weird that its really only noticeable around 1700rpm. Guess I'll keep digging around.

Idle surging is back again after a day of driving.. May have the fuel pressure tested and see if someone can diagnose this better.

 

[uberninja]

Update: Getting pinging/grindy sound from the rear by the tank but only when the idles surge. Thinking its fuel pump related.