My Sportage was having problems
After searching Sportage internet sites, I saw many others had a similar problem
I put a check list of possibilities together for you
Prnt This Out and Take to Your Mechanic

SYMPTOMS
Engine Not overheating
Check engine light is flashing
code PO303 - Cylinder 3 misfire detected
car sputters has no power
if driven for a time white/gray smoke comes out
if driven for a time muffler becomes SUPER hot


Have Your Mechanic Check These:
harness wire to coils (kinda hidden in back) û this is what fixed my Kia
coils
leads
timing
timing belt tension
muffler
o2 sensor
fuel filter
spark plugs
CSP sensor
rust in lines
MAF sensor
vacuum leak
throttle sensor
leaking gasket
mass air flow
ignition timing
cadillac converter
Idle control valve
injectors flooding
crank position sensor
injection flush may fix it
spring missing on cylinder 3
No ground at injectors 1 and 3
exhaust gas recirculation valve
sticking injector comes and goes
2 wires skinned or repaired with tape
gap the new spark plugs they don't come pre-gaped
coolant leaking into the cylinder - coolant covering the piston
Bosch +4 plugs cause the engine to misfire - Go the original spec NGK
plugs are really fouled like an injector leaking down - then flow test is bad

Most of the time the cure for misfire is simply worn out spark plugs. When was the last time they were changed?