Old topic but i got mine fixed. Mine was a vac leak. Check your vacuum it should be someithing like 18-20 inHg, if its less than 16 it will run rough.
The problem was that i had a leak in the brake servo, however if this engine idles rough, it shakes the manifold off the cylinder head, developing another vac leak. So i isolated the brake servo and it still ran bad, and i ruled it out thinking its not there. Then i would reseal the intake and car would run fine, but after a while the brake servo leak will make engine shake the mani off again and problem repeats.
I would advise before swapping expensive 3sge parts do the following:
1. Get a vacuum gauge - they are cheap and super useful and hook it up to full intake vacuum. Beams idles somewhere between 600-700 rpm, so at this engine speed your vacuum should be 17-20. Note misfires will also affect vacuum.
2. Do a compression test. These engines are super awesome and compression on hot engine is spot on across the bar (dont remember exact number but do remember being impressed how even it is)
3. Are you getting good fuel pressure? Check fuel filter clogged/fuel tank sock dirty. Does your fuel pump whine more than usual? I remember reading somewhere that these engines run 60-75 psi, but from own experience can only tell that lower than 45 psi it runs like a dog.
4. Read spark plugs. Do they look lean/rich? Sorry for teaching you to suck eggs, but spark plug readings are only valid for last engine cycle. So idle your engine hot for 10 mins and then check them. Super lean plugs usually indicate no fuel pressure or vacuum leak.
5. Also, ignition coils are not particulary strong part of the engine, but before swapping them test if they are good (there is a guide somewhere on the internet which shows how much resistance you should get across terminals).
6. make sure your engine grounds are not corroded and battery terminals are nice and clean.
7.also check how much voltage does the alternator give out. Should be in 13-14.
sorry for long winded answer hope this helps.
