Information on the car:
2005 Cavalier. Automatic. 88,000 miles
Mods in my profile are mostly up to date (exhaust has changed)
While driving at a constant speed (anything over 25mpg roughly), the engine will surge the RPM's up a few 100 rpms. When this happens you can feel the car surge forward. Sometimes its really bad, other times its barely noticeable.
When under WOT there is no issues in fist or second gear, but in third gear and fourth gear you can feel it cutting out or surging (really sucks when entering the highway). Now this doesn't happen all the time, its random when it happens... but it happens more often when its cold outside and the car hasn't been driving for many miles. For example, If I drive 10 miles to the store it will act up, but on the way back home there are no issues.
My MPG's have dropped (from 300+ per tank to about 250) but its winter, crappy gas and I use remote start in the mornings. So that can explain the mpg issue... maybe.
I have already replaced / tried:
Plugs: Delco iridium
Spark plug boots and springs
TPS
Fuel Filter
FPR
Trans pan drop and filter replacement
Mobile 1 oil / WIX / delco filter since 0 miles
Tried 85 octane, 87, and 91 octane (no change in surging)
Seafoam in the tank and though the booster line using my slow drip induction tool
throttle body cleaned with brush and cleaner
Heat anti water fuel treatment
Misc other in tank injector cleaners
Recently replaced thermostat (surging happened before this too though)
Friends have suggested the TCC solenoid. I have HPT and logged several trips, the TCC locks, unlocks while driving normal, it unlocks under wot or when the brakes are touched. I don't know if it normal, but it locks in every gear 1st, 2nd, 3rd and 4th. Tuning the TCC off with HPT doesn't effect the surging issues. If anyone wants to look over the HPT data log, I can email it or create a video of the log. I don't think its the trans slipping, as I can feel the car accelerate when it surges. The car does feel like it has some power loss, and doesn't have the ol get up and go it did last year.
Any advice would be helpful
below is a video of the surging. I was coming down the mountain, so trying to keep the RPMs at a constant for the video.
Surging is usually caused by running lean, I'd check for vacuum leaks.
Here is the log from HPT if this helps.
