i have a 90 4.0 cherokee and it takes a while to start like it turns over 5 6 7 8 times before it finally starts then it idles fine but when you driving it it shutters and hesitates at lower rpms then after the rpms come up it takes off i gave it a complete tune up and it starts a little easier but the shutter and hestation just wont stop i cleaned the sensor in the throttle body it made a small difference what could this be?