After a few months of chasing a rough idle, and a lack of time to devote to it, I took my car (740T, 133K)to my regular mechanic. Previous to this I had replaced many old hoses, new cap, rotor, plugs, wires, IAC, ECT, cleaned throttle body, had injectors cleaned and balanced in August. Car ran great at speed, good MPG. He checked compression, which he said was very good. Plugs showed car was running very lean. Wiring harness and all sensor connectors were also checked, as was the ECU. He said he didn't like #2 injector. While at his shop, he disconnected each injector connector for me. #2 showed little to no change when disconnected. I asked him about the possibility of a bad intake gasket. He sprayed around the intake gasket, but there was no change. He advised I change it anyway since it was probably the original, and get either 1 or 4 new injectors. Half way home, the car started running worse than ever, and I could here a vacuum leak I had never heard. I discovered when I reached home that now the intake gasket was leaking after being softened by the solvent that was sprayed onto it. I replaced the intake gasket with a new Volvo one. The old one had two huge almost thru cracks around #4 port, which was also distorted into an ellipse, partially blocking the port! I could also see where #2 port had started leaking. Started car and could immediately hear big air leak on bottom side of #2 port. Tightened bolts more and leak stopped. I couldn't believe how tight I had to get them to stop the leak. The next morning I picked up a new injector. Installed it, car idled real smooth.

After a few days of driving it I've noticed a few things. The car still has a slight shudder while idling occasionally. I still may have a small vacuum leak somewhere. I want to put in a another new intake gasket to eliminate that possibilty, plus I didn't like that it leaked at first. I've been running 11PSI. Before the new injector and gasket car seemed felt strong at full throttle. Now with new gasket and injector it pings at 9PSI! I've always run premium. If it is because of carbon build-up, why not before? (Especially since plugs showed a lean condition and when mechanic adjusted AMM he could tell it was very lean also). I'll double check timing, and replace the last couple of hoses I haven't to eliminate them as possibilities. Any thought or observations are welcome. Thanks in advance.