Rough Idle and Poor Gas Mileage 2.3L

[Fitzy]

I have a 1994 X-cab 2.3L that has turned into a giant headache. It started with an oil change at Walmart and they upsold me to a fuel injection cleaning (bad idea). They dumped some in the tank and connected a line to the fuel rail. I had less than 1/4 tank and they told me afterwards to fill it up as it was shaking bad when I picked it up (was fine before). Since then it shakes bad at idle (starts ok). Thought it was down a cylinder. Have taken it to two different mechanics and they don't know what it is. So far have new plugs (all 8), new plug wires, new exhaust, new cat, new battery, had the fuel injectors cleaned (professionally) and flow tested (good), cleaned the MAF sensor (girlfriend's brother did this, ex ford service manager), compression is good on all cylinders (tested), checked for vacuum leaks (couldn't find any), and there are no codes (took to autozone plugged OBD1 reader in) and the CEL has never come on. Sorry for the long post but I don't know what else to do, this thing is driving me crazy. Oh, and my fuel mileage is way down and there is a loss of power. Thank you in advance for any help.

[RobbieD]

Not a long post, and welcome. In all that's listed, you didn't mention the Idle Air Control (IAC) valve; was this cleaned or replaced?

[Dave R]

Did either of the mechanics do any form of cylinder balance test to try to figure out if it's limited to one cylinder or something that is randomly effecting all of the cylinders?

[DCarey515]

Could the fuel injection cleaning have killed the cat?

[Fitzy]

Thanks for the replies. What is the best way to clean the IAC valve? How is a cylinder balance test done and what does it show? The engine will shake pretty rough at idle so that's why we originally thought it was down a cylinder causing the imbalance but we pulled the plug wires trying to isolate a down cylinder but they all "seemed" to be firing, but I'm probably wrong. The cat was replaced after the injection cleaning. I think that it might be starting to use oil now. I went to the local Ford dealership and they said that they charge $94 for a diagnosis, I'm tempted to do this as I want to figure out what's wrong but I hate to keep pumping money into this thing with no results...argh!!!

[97ranger xlt]

did anyone reset the computer? if not disconnect the battery for 10 mins...

and clean the IAC and check TPS.