If I let my 98 GC cool down then restart it the vehicle acts like it wants to die. RPM's go down to 300-400. After a short warm up (2-3min) the Jeep runs great. Immeadiate restarts are not effected. Just recently I have changed the cap, but not the rotor. I know I should have, wasnt thinking it through. I also put new spark plugs (properly gapped) and new wires in. I also changed my radiator, the cap on it, and removed the thermostat for the warmer months. The shuddering problem started after I changed the radiator, but before my little tune up. I even threw the thermostat in for troubleshooting, but of course no difference. No check engine, no other problems. Any ideas?