4ks injectors fouling (kinda long)

[roger@mostro.sps.mot.com (Roger Albert)]

Hi all,

So, I've written a lot the last month or two as I've tried to sort out
the fuel/ignit systems of my 'new' 4ks.  I had replaced a lot of old
ignition stuff, the WOT switch, the filters, and adjusted everything,
but still had (usually) a poor idle and horrible bog upon acceleration.

Running out of time (visitors from Germany coming who I'd promised my
truck to, which means I actually _needed_ the car for once)  I finally
decided to let a mechanic take a crack at it, all the time fearing some
horrible financial toll.

Well, to make a long story (fairly) short, it was badly clogged injectors
with not only a poor spray pattern, but actually more of a dribble pattern.
Counting new seals and cleaning, the car was fixed inside of a day for $51

I was happy.

So, two days later, the problem started gradually returning.  I dropped it
back off at the shop and asked that they take a look and try to find the root
cause.  The again of course cleaned the injectors and then drove it quite a
bit for a few days.  Satisfied, they gave it back to me today.  Seems fine,
so far.  No charge either.  Cool.  I'm a little paranoid as to whether it's 
really fixed for good or not though.

Any ideas as to what could have caused the recurrence?  What rubber or other
possible contamination sources are there between the fuel filter and the
injectors?  

1 Could some rubber fuel line coming from the pump be deteriorating?

2 Inside of the injector lines?

3 Pressure regulator?

4 Fuel Distributor itself?

5 Deteriorating tank (or gunk in it) that's getting past the filter???

I did put a new filters in  (had the problem before the change, so I 
don't think I introduced any grunge during the change) and just got an
easily available Purolator filter at the time.  Anybody know if that's
just a crappy filter and thus, if its a case of grunge getting through
the filter, whether a genuine Bosch would be better?

Sounds like I could fix it myself if I had to next time, but I don't
fancy doing so every 200 miles or so.

As usual, thanks for any help.

regards
roger