Clutch

 

I have an update on this issue: I had the transmission rebuilt and clutch replaced. There was a steady leak and an obnoxious rattle, so I caved and had it redone. This did not solve my problem though.

Now I have the issue in every gear. When accelerating, there is a 50/50 chance that it'll accelerate immediately. When the issue occurs, I can have the gas pedal held down at the same position, and the truck sporadically accelerates causing it to buck. Also when this happens there is a noticeable sputtering in the engine before the bucking. When I bought the truck I replaced the fuel pump to get it running again. I used an "OEM" brand pump (not a Denso). Could this cause the irregularity?

I have also taken it to a mechanic that has worked on old toyotas for 30+ years and he said that it could be caused by the EGR system, but since it wasn't throwing any codes not to worry about it. Any ideas on this diagnosis?

 

You can test the fuel system. Get the banjo adapter and rig an inexpensive fuel pressure gauge to the cowl, this will let you see fuel pressure at cruising speed. You can plumb the fuel return line off the regulator into a catch can then jump the fuel pump diagnostic port and measure what you have after a minute (iirc it's something like 500cc per minute? I always seem to forget this number)

You can fashion a temporary block off for the egr by cutting a section of aluminium can that fits between the intake and EGR inlet, sandwich it between two new gaskets to prevent leaks, this will prevent EGR flow and eliminate it as a possible cause.

I don't see anywhere that you posted test results from the throttle or air flow sensor, did you try these yet.

I don't see that you ruled out the exhaust system, did you try the test of disconnecting it near the front?

Once you have exhausted these tests we can move onto more things like the ignition or oil pressure and timing chain. (I'd lean towards the later part of that, the initial throttle change can cause the cam timing to shift. What happens is when the crankshaft pulls on the chain the cam can accelerate faster due to the lower mass and a worn tensioner or low oil pressure this results in an advanced valve timing, its what causes the chain to jump off the crank sorocket. There is also an inverse reaction where a sloppy chain stretchs and the valve timing retards.

(It would also maybe be better to give the RPM range it's occurring at than the road speed since the road speed has to many variables)

 

Sorry for the quiet period. I have another update. I tested the AFM numbers and they checked out. Because I was told by a dude that owns a yota scrapyard that a cone filter might help, I threw in LCE's kit.... Still had the same problems.

After @Co_94_PU advice I started looking into the exhaust. I had been saving up money for a new exhaust system anyway since the stock one had leaks and holes everywhere. I bought the LCE header and backend. Since together they cost a lot, I started with the Header for obvious reasons. Once I installed the header, a new gasket and a new O2 sensor the problems stopped . Thanks to everyone for all the help and advice through this. It seems to me that it was probably an exhaust leak issue, and maybe even a malfunction of the old O2 sensor.

Bonus Redneck Picture: Because I didn't want to completely lose my hearing, I rigged up a connection to the backend of the stock exhaust until I could save up for LCE's.