4.0L Hesitation/ Stumble on acceleration
Hello, I have a 1990 Cherokee with high mileage (179k) on an original engine. The truck idles and runs fine, but when the throttle is just barely cracked off idle it stalls, nearly dying if held in that position. While driving, it produces a short hesitation just off idle while accelerating, then smoothes out and runs fine. I have attached a vacuum gauge to the intake, vac. normal at idle, cracking the throttle and holding it just barely open drops vacuum to almost nothing, engine runs rough and stumbles around, eventually smoothes out and runs fine at same throttle position.
I have replaced the oxygen sensor and cleaned the throttle plate and body, with no change. Would a worn timing chain produce these symptoms? Any help/ suggestions/ comments? Thanks! Regan