I am a newbie to this site so forgive me if I ask redundant questions or miss the obvious. All and any information is greatly appreciate.

I am attempting to assist a friend with a 2001 Sentra SE, 2.0 liter, 5 spd. 70,000 miles. We have a performance issue. After 4,000 rpm in the full trottle position the acceleration falls off. It revs nicely and acceleration is good until it hits about 4k, at that point it acts like the timing gets retarted. If you take it up to 5k at part throttle it feels ok, but stomp it down and it stumbles at 4k and stays flat all the way up.

I checked the wires, used some cleaner on MAF sensor, inspected all intake hoses to no avail. Also, no check engine light and no errors. I will try some new plugs tomorrow and hopefully by then, someone will give me an idea on what to look for.

Many thanks from the Motor City,
Tim