4Runner Jerking after Shifting Gears

Hello 4runner enthusiasts. I have a 1994 3.0, 4x4, 5spd with 230k miles, which I have owned for 11 years/45k miles. The problem first started where I would shift into 3rd gear and upon completing the shift, she would give a series of 3-4 quick jerks/bucks before settling in and accelerating normally. This would only happen in 3rd gear. However, this has now progressed to where it happens when shifting into 1st, 2nd and 4th gears as well.

Some observations:
-It does not always happen every gear shift event, but is most common going into 3rd
-1st and 4th gear jerking is less common and 5th shifts smoothly.
-Happens regardless if engine is cold or warm
-Jerking only happens for a couple seconds and RPMs stay relatively stable, maybe a slight drop but they are not running away like a slipped clutch
-I do not hear or feel any grinding noises
-Definitely not a skill issue as I have owned her for nearly a decade before this started happening.
-There has been no transmission work done since I've owned her and previous service records were not provided by last owner
-During an alignment a couple weeks ago, the mechanic noticed a worn u-joint in the rear driveshaft. I was hoping that might be the problem, so replaced both ends of rear driveshaft with Spicer u-joints....but this did not result in any noticeable change in driving.
-Fluid levels in transfer case and differentials are SAT.

I've searched this forum and the internet for something similiar and not finding anything. Does anyone have any insight on what could cause this? Or ideas for troubleshooting to narrow this down?
Any help would be much appreciated. Thanks!

 

Shooting from the hip here, but possibly a dirty MAF (might be an 'air flow meter' in your case)? I once had an '88 22R-E with a sticky air flow meter that had similar symptoms. It had a 'butterfly' type regulator, and I diagnosed it by spraying lube on the upper and lower pivot points of that regulator. The unit looks similar to this.

 

When was the last tuneup? Spark plugs, wires, cap, rotor, air filter and fuel filter.

 

^agree

 

Thanks for the responses! Daddykool, I did lubricate the hinges of the "butterfly valve" inside the volume air flow meter as suggested. It definitely operated manually much smoother post-lubrication but can't say i've noticed any performance improvements after putting some miles on it this week.

Justthemechanic/ChessGuy - I'm ashamed to admit I can't remember the last time it got new plugs and wires, and these driver side spark plug pics sure look rough. Air filter is one of those K&N filters the previous owner installed and I've been religious about cleaning it per the vendor recommendations. I replaced the fuel filter a couple months ago.

From what I can tell reading these plugs on cylinders 2,4,6 I have a lean condition - based on the light grey buildup? I know they are worn way beyond their service life as well. I'm learning as I go here...

 

Start with a tuneup and ditch the K&N filter.

Those plugs look terrible, what is the factory service interval on those? I’d imagine 30-60k by 1994 standards

Those ashy deposits are not normal; possibly from air filter oil. Are you using any other fuel or oil additives?

 

Install new NGK BKR5EYA spark plugs, Denso or NGK spark plug wires and Denso distributor cap and rotor. The recommended change for these items is 30k miles.

I am not a big fan of K&N type air filters but if you operate in a non dusty area it will be okay. Be sure not to over oil when you clean the filter.

 

I'll definitely look around for a factory air filter, I had not considered the K&N oil as an engine contaminant but that makes sense.

White TuRD - I'm not using any additives (except that K&N air filter oil, oops). I had this 4runner abroad where it was subjected to extensive mileage of dusty off road trails and even worse fuel of questionable quality would be at times the only fuel available. As a result of that, it has been on my radar to replace the fuel pump and fuel injectors (with OEM quality in mind) soon.

Justthemechanic - My replacement spark plugs I have in hand are the NGK BKR5EYA. The existing wires & distributor cap/rotor are much better looking than those plugs but I'll replace those too. If I keep the K&N filter i'll minimize the oil and fortunately I live in a dust free area.

I appreciate the feedback! I suppose I should have completed some of these essential tune-ups/replacements to see if this solves the post-gear shift jerking, but I had it in my amateur mind that I'm experiencing some kind of mechanical related issue and not rooted in spark/fuel delivery. I'll report back drive performance after getting these swapped out.