it sputters

[Tom Love]

The 4kq came home with a sputter at the lower rpms around 3000. I tried to
do the regular running cleaner through the fuel system and no luck this
time. The cap and rotor are new and plugs have about 2 mos on them. I pulled
the plugs and 1,2 & 3 look great and 4 has a little darkness but 5 is black
and dry.
As I mentioned, the sputter is only at lower revs and in addition with half
to full throttle, there is no sputter at all.
Injectors? Gasket?.
The car just got a steam bath when the return heater hose went the other day
and the performance problem occured at the same time. Car never heated over
half way because I caught the leak just as it was happening. I bypassed the
4 and 5 plug wires with known good and got no change.
Any ideas?
TIA as always