1991 gs 1.8L standard, shudder at low RPMs even when not in gear. module,cap,roter,plugs,wires replaced, still acting up.

which engine the 3.6? v6?
that shudder is called MISFIRE.
get a tune up yet, even $1.49 spark plugs?
no its not the trans,
if it dont slip, its not trans, (see RPM races? that is slip or too low gear)
if it shifting to the right gears, its not the trans can you count them?
is the CEL lamp glowing or flashing driving, is yes, that means
scan me now. in fact scanning while it shudders, is like (magic)
why start guessing, do a tuneup,
then scan it.
if its is misfire the PCM will tell you what cylinder misfires.

are your spark plugs 6 years old, if yes, why?
going for 200k miles on them.?

not knowing the quality of workmanship used in the engine rebuild, it is difficult to answer exactly what is wrong
plugs and leads will not be faulty
I think the clue is in the remark about the carby being replaced and it ran a bit better
that indicates ,along with the very rich settings, that it could be an valve timing problem
I suspect that the cam shaft lobes are damaged or the timing chain gear is loose on the cam shaft
running well in the beginning and then slowly failing all points to the cam shaft lobes, cam followers or loose cam gear

If not wrong this engines also need a valve lash adjustment time to time even do this littl eng. 22RE runs rough normally, try it wont hurt.

Timing or throd position sensor

I have a 1991 Cadillac Fleetwood 4.9 120000 miles, I have the same problem. replaced plugs,wires,cleaned throttle body, and O2 sensor and have same problem. Taking it to a GM shop on 02/24/10.

check the egr valve it mat be stuck closed ..... code PO404

time for a tune up....plug wires and coil wire are arching out under load....replace plugs,wires,cap and roter...will eliminate problem...good luck....Lee

By module do you mean computer? There's nothing wrong with it. Yea, replace all ignition components with new ones. New cap, rotor, wires and spark plugs.

Hi Marksberry, I have a suggestion to make. Please check your gear box mountings for wear. If they are torn, please replace. Did it solve your problem?

Your flywheel sound like it has hot spots on it, making the clutch chatter. You might need to pull the flywheel off and get it re-surface. This is like turning your rotor, or brake drum. If you pull the flywheel, you will see discolor spots on your flywheel. This is called hot spots, and will make the clutch slip.

On the other problem, have you changed to fuel filter and fuel pump. It almost sound like your running out of fuel????