IMHO, that doesn't really sound like a problem to me, but there are lots of experts on the forum who may have a different opinion.
The Lower Plenum shouldn't really be a problem at such low RPM as the vacuum servo doesn't operate until 3000rpm. If you think you have a problem with the lower plenum, try these:
1. Raise the hood and listen to the engine idling. If you hear a rattling or a hissing noise which appears to come from the front of the engine (just under the plastic cover) you may have a worn out lower plenum. If you do hear a rattling, get a long screwdriver, and place the pointy end against various parts of the engine and hold the blunt end against your ear - you should be able to find where any unusual noises are coming from using this "screwdriver stethoscope". SAFETY POINT - Watch out for the fan <img src="/forums/images/graemlins/wink.gif" alt="" />. The hissing noise could indicate a vacuum leak so check around and see if you can locate it - a worn bushing on the front of the lower plenum causes this.
2. Take the plastic cover of the top of the engine. At the front left (viewed from rear of vehicle) of the plenum is a gold coloured vacuum servo - this operates the valves in the lower plenum. Rev the engine by turning the accelerator linkage by hand, and watch to make sure this servo operates at 3000 rpm - you will need someone in the cockpit to watch the tacho.
I would say though, that I find my 95 SR doesn't pull too well at low revs with the overdrive engaged - I frequently drive with it off in heavy traffic.
Cheers <img src="/forums/images/graemlins/smile.gif" alt="" />
