Sam Spade wrote:
Pilot: "SoCal Approach, Piper 1234B is 10 west of Paradise on top at
5,500. Request ILS approach to Chino 26 Right."

ATC: "34B squawk 2133...34B radar contact, fly present heading for the
Chino ILS 26 Right. Descend and maintain 4,000."

Did the controller issue an IFR clearance?

Nope. What you want to hear is "cleared to the Chino airport". Then
you're IFR.

On the other hand, "maintain 4,000" sure sounds pretty IFR-like. My best
guess is the controller probably meant to issue you a clearance limit of
the Chino airport but mis-spoke. On the other hand, he could still be
moving other traffic around, and won't be able to issue you your clearance
until he's got the blips separated sufficiently.

But, there's no need to guess, just ask the guy, "confirm 34B is IFR this
time?" He'll either confirm that you are indeed IFR, or he'll tell you
that you're not yet and why. It's great fun to nit-pick the FARs and AIM
and second-guess what a clearance must have meant on usenet, but in the
air, if you're ever unsure what the controller meant, don't play games; ask
for clarification.