Thottle surge/drop at speed

It's not common, but I'd check the vacuum ports on the throttle body that control the vacuum modulator for the EGR valve. Should be three. The recommended method is to clean them when the throttle body is removed - solvent and compressed air, but you might try removing the vacuum lines and using solvent and compressed air from the outside. Do not use any type of wire that could mar the openings. When I cleaned mine with the TB off, a little glop of residue was cleared from the smallest of those three orifices. Afterwrd a slight part throttle hesitation seemed to have improved. EGR is off at idle and full throttle, but on during part throttle - modulated by those vacuum ports.

I like the Berryman B-12 Chemtool, and it's only around $2 or so. The main consideration is that it must be emissions control safe. If by "dunk" you mean "gunk" - I recently bought a can of that just to clean the exterior of my old Toyota truck water pump from (oil leak) residue prior to removal. The Berryman seems to instantly liquefy oil and varnish, but the gunk didn't work anywhere near as well from what I saw.

How would you use that with the throttle body still on the car? My idea was an aerosol spray. I've got a gallon of that type of carburetor cleaner, but I haven't used it since I last disassembled and cleaned a carburetor.

water afterward. Perhaps there's some newer version now. If you're going to take the throttle body off the car, then check the manual and follow all the steps for adjustment.

============================== That would be aerosol and compressed air. When I saw that bit of goop fly out, it was after being soaked with solvent, but then also hit with a blast of compressed air - and that is the method given in the factory manual also.

That would be much better. That's the way it is supposed to be done. Plus, then you can clean the back side of the throttle body that tends to get fouled with PCV blowby and also check adjustment on the TPS more easily. Read the section in the manual about throttle body cleaning and they'll give you all the steps and adjustments - there were a number of items, and on mine, they were all in need of adjustment.

That would be much better. That's the way it is supposed to be done. Plus, then you can clean the back side of the throttle body that tends to get fouled with PCV blowby and also check adjustment on the TPS more easily. Read the section in the manual about throttle body cleaning and they'll give you all the steps and adjustments - there were a number of items, and on mine, they were all in need of some adjustment.