My '91 L98 has developed a low RPM stutter/stumble. Just seemed to happen out of the blue. The car is in great tune. New plugs wires cap and rotor last year. All the fluids are topped up. Was running great then out of the blue it started having trouble in the low Rpms. I can press the throttle a lil and just nothing and then it will jump and then stutter again. If i really mash the throttle it will kinda push through it but the car doesn't seem to go like once did. I checked to see if i had burnt a plug wire but couldn't find anything, i tried following and listening for vaccum leaks but i couldn't hear or find anything that my eye or ear could pick up, but i aint a pro either. The only other thing i can think of is maybe my gas. I usually use 91 but i had put 87 in and ive never had an issue with 87 previously. But thats the only thing i have done just previous to my issue arrising. Please dispense with any advice. I would rather not take it to a mechanic, but i do have a competent one atleast.

 

Try taking the EGR vacuum line off the throttle body. It hooks into the bottom on the driver's side. Take the line off, plug the vac port and see if it goes away. If so, EGR valve. I had a slight stumble off idle and unplugging the EGR solved it.