Here's the info:
MY93 900SE body, added T16S engine (and running gear). All work done by an independant Saab specialist.
Car starts and runs fine except an intermittent cough. It can be under light throttle or full throttle at various revs. The cough is like a drop in power as if there is no throttle. It can be a single one or a splutter of two or three. I cannot make it happen at will and its always such a suprise I don't have time to see what the boost guage is doing. Oh it also packed up on me and was diagnosed as failed fuel pump. Nice trip in an RAC truck after 2.5 hours at -5C waiting with no engine. The fuel pump was replaced - still coughing It does it from cold or when warm.
Plugs were the corret NGK, but I put new ones in anyway (7mm gap). Ouch said the autofactor when he was charging me!
I changed to super unleaded and thought the cough was not so severe (it had felt like whiplash on ordinary unleaded). Still there in frequency though.
I went to Shell Optimax and it was a noticeable softer cough, more an ahem, but still similar frequency.
The end of my mechanical tinkering...
The garage have:
Replaced fuel pump
New fuel filter
Adjusted air mass meter (was rich)
Replaced FPR with 3 bar one from 900i
New Distributor cap
Boost Control valve appears OK
It still coughs, but it took 33.8 miles to do it after I left the garage, then did it about 15 times in the next 60 miles. The car feels really smooth and responsive with plenty of whoosh except for this cough which tends to make me nervous about overtaking. I appreciate why their road test didn't find it!
I am not boosting into the red with fall back only about 3/4 through the orange. Garage has suggested staying away from optimising boost till we sort the problem.
Any ideas please? I've had the car a month and its incredibly frustrating and time consuming to keep taking it to the garage. They are incidentally being very understanding.