Expert: Von Sudderth - 2/15/2008

Question
I'm in the process of replacing my 98 Nissan Altima Cat and found a 5 inch crack in my engine manifld off the second pipe, 3rd cylinder (of which I replaced a fouled plug previously).  It's obvious this could be causing some of the problems I've been experiencing, but could it cause the car to only be driveable at speeds of 30 mph and stalling at initial turnon, until warm up.  I've only been able to look at the Cat outlet and it doesn't look burnt, may be ok, but my cost for self repair is increasing.

Answer
Randy,

If there is an exhaust leak it will cause problems with both the cylinder efficiency as well as the oxygen sensor.  I would first correc the exhaust problem and then reset the computer, drive the car for three days and see what comes up.  Other things that can cause problems are mass airflow sensors, idle air control valves and throttle position switches.