My 2000 2.5L manual trans 2wd ranger is doing something strange.

i just bought it, it’s in ok shape, I’ve done a lot to catch it up on maintenance, but this one problem is persistent and I can’t figure out where to start with diagnosing it.

Every once in awhile it has a violent jarring feeling. It feels like a fuel cut, but way more violent.

I’ve put 100+ miles on the truck now and it’s happened maybe 10 times.

so here’s the deal, it occasionally stumbles as if there’s a vac leak or something, especially on cold start. It doesn’t always happen and there’s no real telling when it will happen. And then it’ll suddenly clear up and everything acts normal. Especially once the engine is warm.

I’m not sure if the jarring issue is related, but what happens is around 1-2k rpms, warm or cold, it’ll start to stumble and then it almost acts as if the engine tries to lock up for a split second. It’s very violent and accompanied by a metal thud or metal scrape sound.

Sometimes it happens letting the clutch out in 1st, other times I’m cruising along in a neighborhood or something at low speed and I’ll give it a little throttle to get up an incline or come out of a corner and it will happen.

It’s pretty rare it happens but it’s so violent it has me worried.

i have been only been able to duplicate it once with the hood popped and bumping the throttle with my thumb. When it happened the engine slung itself to the side of the engine bay as if the motor mount just fell off, I mean it’s that violent.

But the motor mounts and trans mount are perfectly fine.

I was catching up on maintenance the previous owner skipped out on, so I have installed new:

plugs
plug wires
fuel filter
pcv hose
radiator
water pump
timing belt

to no avail. The problem still persist. I was banking on it being the fuel filter, but the old one I removed looked fine and the fuel coming from the tank was crystal clear. It’s not bad gas either, as the tank was basically empty and it’s got a full tank of fresh gas and 100 miles put on it now.

I’ve been asking around everywhere and I’ve found several others who has similar problems, but no solutions. Only one person had a solution but it involved blocking off most of the iacv, I don’t think they understood what I was saying, I can’t imagine the iacv is the problem because it’s not something that happens at idle and it’s so jarring.

The metal thud / scrape noise I think is just from the engine throwing itself about the bay so violently but I’m not sure.

it’s just a single instance for a moment and then it goes back to everything being normal. I mean 90% of the time the truck acts completely normal.

asking around people have suggested everything from the fuel pump to the clutch springs. I can’t imagine it’s the clutch springs because it’ll happen well after I’ve let off the clutch. I don’t suspect the fuel pump either since it runs fine most of the time.

I’ll add I’ve been an automotive and motorcycle tech for about 11 years now and I’ve never experienced anything quite like this.

The only thing wrong with the truck is a slit in the catalytic converter, it’s a sizable exhaust leak. But I wouldn’t imagine this is causing this random violent behavior. Maybe the stumble, but not the jarring effect.

there are no codes either.

Any ideas where to start running test?