Blowing Sound And Rough Idle?

I have 2002 Fiesta Finesse 1.4

6 Months ago it was
running very rough so I replace the sparkplugs, ht leads and coil pack and this
fixed the problem however a month later the timing belt slipped which damaged a
valve.

On inspection the garage discovered the oil hadn’t been
changed in years and it was like lumpy black goo.

Oil was changed valve replaced and timing belt fixed.

Now this is the problem I have been having lately

The car started juddering when accelerating and the engine
warning light came on so I checked the ht leads and one had become loose
however the metal part of the lead was still attached to the plug.

Eventually the lead
was replaced and the metal removed from the plug

Car has stopped
juddering but the engine light was still on so I checked the oil and it was
just below the minimum mark. Topped up oil but engine warning is still on and
for the past week it idles rough and makes a blowing noise when excelerating. Exhust
system is about 8 months old.

Has anyone got any
ideas I really can’t afford another large garage bill