Not real sure but just a suggestion. You may have a bad coil pack. Give me a minute and I'll see if I can find out how to check them.
Here it is...
Ignition off...disconnect the elect. connector from coil (there are 2 of them). Using an ohm meter, connect the positive lead to the center of the primary term and the negative to the outside terminal. Reading should be 0.3 to 1.0 ohms. Then check the secondarys where the plug wire connect. Each is paired to a companion cylinder so connect the leads from 7-4, 8-2,1-6, and 3-5. Reading should be6.5 to 11.5 K-ohms. If any readings are bad, then it is a bad coil.
At least you can rule out the packs by doing this. All this info was found in Haynes manual. It also says there could be a problem with fuel management system but it is a pretty invlved check.