Got any codes???
I hope you put in Motorcraft Plugs, Autolite is acceptable, but the Zetec realllllly likes the Motorcraft plugs. Bosch will just cause it to misfire/shake.
If both of the above are good, then don't worry about adding chemicals to make your car run right, just get the basics right, and start working on specifics from there. Pull your MAF and clean it with non residue contact cleaner (read up on it, don't just clean it without understanding how to), pull the TB and scrub it with a tooth brush and brake clean, pull the PVC valve and check it for proper opperation and clean it if it is good, thank Ford the ZX2 does not have an egr system, check your wires/coil pack for arcing, corrosion, damage, etc..., air filter, vacuum leaks.... I could go on and on. Use your scan gauge to monitor your sensors to see if any of them are acting funny, like a slow O2 sensor, coolant temp or air temp sensor that is off, etc.... You'll find it, you just have to be persistant and understand that the difficult job of finding these problems is what will make you a better ZX2 mechanic, then your mechanic will ever be.
BTW, Scangauge II is on it's way to my house
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