Help! Engine shudder at 4k RPM

My 3.4l 2002 (200k miles) Tacoma's timing belt went out on the highway between Idaho and Utah. I got the belt replaced but ever since then the engine shudders right at 4k RPM. It only happens every once in a while (when I shoot a gap on the freeway) so I've let it go a while.

Right when I get to 4k I can feel the whole motor shake and lose power. I have to back off the gas or it keeps shuddering. The guy at O'Reilly says that no codes come up relative to this and that if it were the cam position sensor there would be a code.

Some background. This is a really beat up truck (so I'm selling it soon) that I regret buying even though I love tacomas and it's my second one. I've had all sorts of issues with emissions, I've had to replace sensors etc. because the previous owner didn't change the oil. (It burns oil so I'm assuming that's what happened.

I recently didn't pass emissions and they said one of my cats was destroyed. I think it was the first one. I think they replaced the second one, as I can see the shiny metal halfway down my truck. Maybe it's the broken-up cat that's blocking exhaust and causing the shudder?

I did have the engine light come on but it was P0301, misfire on cylinder 1. I recently had a tune up but they didn't replace the spark plug cables/wires so I'm going to buy wires and see if that fixes the misfire issue. I think it's unrelated to the 4k RPM shudder.

I really could use your help as I'm trying to sell the truck. I have a friend who's willing to pay good money for it but I don't want to have to tell them it has a serious engine problem that's unsolved. Thanks so much!

 

I'm glad we are not friends.

 

Shoot the gaps on the freeway at 3900 rpm

 

Of course I'm going to TELL them. The point is I want it to be FIXED when I do. haha They've wanted to buy it ever since I bought it.

 

Not to change the topic OP, but my '01 has developed a "shutter" within the past week too, feels like starving for fuel/air. Started @ about 65mph, then from 45mph+. Drove it yesterday morning to get food for my nephew & it began to do it at acceleration from a stop sign. I changed my air filter today (haven't done since I bought it - it was nasty) and have plugs & wires on the way. I'll be removing the throttle body & cleaning that at the time of the plug changing. Good luck with everything & share what you find.

 

Well I read about exhaust backpressure online. So being the mcgyver I am I thought "how could I relieve pressure?". I pulled the upper oxygen sensor and put it in a plastic bag with a lighter taped open so the bag would fill with butane and the sensor wouldn't pick up to much oxygen. I revved the motor and.... same issue! I guess it's not backpressure....