Yes, you probably have air trapped in the top of the inside piston (which has no bleeder screw), or in the brake line between the ABS control unit and the caliper. You will have the do the "caliper dance":
- Unbolt the caliper from the hub assembly. Push the pistons all the way into the caliper. If you are using a pressure bleeder, like a Powerbleeder, place a piece of wood between the brake pads and/or pistons before pressuring the master cylinder reservoir so that the pistons don't pop out.
- Try to hold to hold the caliper higher than the ABS control unit (inboard of the left front fender, above the left front shock mount) for the whole procedure.
- Hold the caliper so that the cross-over tube from the inboard piston to the outboard piston is at the top (basically upside-down). Bleed a little fluid out of the outboard bleeder.
- Rotate the caliper outboard side up so that any air in the cross-over tube can make its way to the outboard piston (the air will always try to rise up on top of the fluid). Bleed a little more fluid out.
- Finally rotate the caliper so that it is right side up (with the bleeder screw on top) and bleed it again. At some point in this dance, air bubbles should have come out in your bleeder outlet tube.
After introducing air into the system, it can easily get trapped on the inboard side, so the goal is to work the air out by letting it rise to the top in each step. The intermediate bleeding is to encourage the air to move towards the outside piston, where it can be expelled via the bleeder screw.
This should make things better. You might have to do it a couple of times if you don't get back to your previous pedal level on the first try.
For those who are about to change their caliper pistons, the best way to minimize this problem is to pull the old pistons out one at a time, facing up so that no brake fluid comes out, and then completely fill the cylinder bore with brake fluid before pressing the new piston in. The goal is to try not to introduce any air into the caliper. Yes, it will be a bit messy when the excess fluid runs onto your hands, but it could save you from having to do a lot of "caliper dancing"...
p.s. If you are going to bleed the clutch, you have to be EXTRA CAREFUL and make sure to overfill the master cylinder reservoir, because the fluid supply nipple for the clutch system is very close to the "FULL" level on the reservoir. If you let the fluid level get too low, bleeding the clutch will suck AIR into the clutch line instead of fluid...