/// Warning Keith--- The 0-rings in the injector holders are high temp. Use only Volvo parts or insist on the high temp 0-rings inside the holder. These should cost $1+ each not 35 cents. If you use the regular 0-rings they will shrink, harden and be almost impossible to get out withour breaking the holder. There is a thinner 0-ring on the outside of the holder and it can be either type since it can be cut off. The advise on the intake manifold gasket is good, try spraying carb cleaner around the gasket and see if the idle clears up. Poor idle is usually unregulated air. --Replace the 0-rings first.

The seals are likely your culprit, but while you have the injectors out disconnect them. Throw them in the 1-gal of B12 for a couple of hours and reinstall them with the new seals. Now, run a regular regimen of of one botle of Techron every 1500 miles and you won't have to pull the injectors again.

Onkel Udo

Have you checked for a leaking intake manifold gasket? A new gasket

cured the rough idle on my '78.

If the injectors are loose in the holders, you have vacuum leaks. Poor spray pattern is also possible. Over the years, the plastic holders wear and even with new seals, the injectors can be loose. If you don't know how old the injectors are, I would replace them along with the holders and seals.