Hey all,

I am the owner of 1994 4runner with a V6 3VZE and a manual transmission. Recently I went to start up my truck and it turned over fine, but once it started running the noticed it was idling low and rough. Anywhere from 200-800 rpms. I let the truck keep running for a minute and decided to take it around the block. First when shifting I noticed a slight pause from when you let out the clutch to when you pressed the gas, not how the truck was shifting before this (but maybe its just me). Got almost around the block and and threw it in neutral to stop and the engine cut out on me. Stopped and started the engine back up and had to immediately press the gas to keep the truck from stalling out. Did a little bit of research online and read it could be a multitude of things. Wanted to know what you all thought. Thanks, TresedToyota01

 

Welcome!

Just like you have read, your problem could be many things.

Did your Check Engine light come on when the engine started running rough?

Check the rubber intake boot for cracks and splits. If there is a crack letting in quite a bit of air, it will mess with the fuel calculations.

 

The check engine light did not come on. Checked for a crack on the rubber boot and couldn't find anything. Going to try and replace the EGR valve and see where that gets me. Will let you know what happens.

 

Idle speed is controlled by limiting air flow. Start at the air filter and work your way back to the iacv. You might find an air filter full of mud, a crack in the accordion hose, a blockage or malfunction in the IACV.

 

Yes the most important calculation being do I turn on/off the fuel pump


It's not the AFR that is the major issue it's the fuel pump cutoff in the VAFM in the case of a leak between the VAFM and throttlebody.

FYI..




The important bit is the ignition timing. The vafm works primarily as a load sensor. When you go from part throttle to open throttle the vane opens fully briefly this triggers the ignition to retard momentarily and allows the crankshaft to speed up with out hammering the bearings flat or outpacing the cam, the vane then stabilizes somewhere between where it was and fully open. (It has auxiliary functionality that help in the AFR calculations, and functions as a back up to the tps THA signal)

This load sensing is what triggers the failsafe (over boost cutoff) in the RTE.

You'll notice similar effects on all of these L-VAFM engines. When people talk about "engine lagging from 2000 till after 3200 rpm" that's the load sensing in most cases. If you slowly open the throttle and allow the crankshaft to gently accelerate there is no ignition retard and it glides right up, but if you hammer the throttle in 5th gear you instantly loose a lot of HP..

It's even more exacerbated by the automatic trans down shifting out of O/D since there is a huge surge of airflow across the vane. (Again a big cause of the RTE triggering over boost cut off)

(Yes to much free time today, I got wordy!)

 

CO_94_PU thanks for your words of wisdom. Went through the whole system from air filter to IAVC, cleaned it out, checked for damage and nothing. Going to look into what you talked about in your most recent post, when I get time(I appreciate the long explanation).