Volvo: 1992 Volvo 960/sudden/rough running engine/, vacuum hoses, 1992 volvo 960

Question
I have a 960 SW with 117000 miles. Was runnung fine until after an hour stop at the grocers. When I started the car it hesitated and ran rough at idle. I managed to nurse the car home. (7miles)
I checked the spark plugs...they seem to be normal. I checked the vacuum hoses and hose to the EGR... seems OK. There is no check engine light or any indication of a warning code. Any help would be appreciated. Thanks.
Steve

Answer
Steve,
With out a trouble code it will be tough! How is the fuel pressure and has the filter been changed? Fuel pressure does not itself post a code. If the pressure is out of range you may get a fuel trim code. A clogged fuel injector, but electrically good will not post a code. A vacuum leak say in the intake manifold will cause a rough running engine, and take a good deal of time to post a code. EGR valve on at idle will cause a rough running engine. But there is a good chance that a code will occure.
On some of the early 960's carbon would build up on a intake valve and not allow that valve to close properly, try a compression test. In those early days we replace the cylinder head, with one that had a new and improved valve guide that was a bit shorter so less chance of carbon to hold open a valve.