Precision Engineered makes a "speed chip" mod for PT Cruisers which "tricks" the engine's computer into thinking the intake air is cooler than it is, thus increasing the richness of the fuel mixture.  Rather than an actual computer chip, it is a variable resistor ... but nicely manufactured.  Installation requires cutting the wires to the air temperature sensor and crimping on blade connectors.  For the PT Cruiser, that's a tricky and tight operation as you have very little wire with which to work.  I soldered "pig tails" (wire extensions) onto the sensor plug to make things easier, especially mounting the chip.  I run a K&N cold air intake (highly recommended for some extra power) and fastened the "chip" to the intake tube near the sensor plug.  You do have to be careful to keep the hot wires and signal wires straight.  The K&N added noticeable power, and the chip definitely added to that.  Combined with a DynoMax muffler, those mods make my PT considerably faster than the average non-turbo PT ... and the muffler gives a deep, booming exhaust note (unlike those coffee can mufflers kids put on their Hondas, and which sound like oversized leaf blowers).

You can take on this project if you have some electrical tools and know how to use them ... soldering iron, wire cutters, wire stripper, connector crimper and shrink tubing.  You definitely can't do it "with a pair of pliers", as some chip makers claim.  Neither are you going to do it in 10 minutes ... but the effort is worth it.