4Runner, 3.0 V6, manual '92.
So I've changed plugs, wires, ignition coil, air filter, all vacuum lines, checked fuel pressure regulator, TPS and VAF and it's stumbling anyway.
It idles perfect, and starts perfect too, but it can't keep equal RPM's when these are higher. If I try to drive at 60 mph - 2,500 RPM it starts to stumble, then I must derpress accelerator all the way or let it go. I don't know what to do next so please help.

 

How about your fuel filter?

 

Sounds like you've pretty much excluded the electricals. I'd think fuel issue, too; either fuel pressure ( pump going bad, filter clogged) or dirty injectors (if non-carbureted). Might also be the fuel pulsation damper, but I'd prolly put that last on the list.

Mike in AR

 

Fuel system is fine I think. Anyway my 4R rides on LPG (liquid petroleum gas) and the same symptoms (on gasoline and LPG).

 

I saw in some old posts from last year you had a similar problem that ended up being the coil; could it be bad again? if so, you have some type of electrical problem that is burning coils....

 

I thought it was a coil, but as it showed up it wasn't. The problem is back and the coil is fine now - I've checked it with ohmometer and it's ok.

 

My next guess would be injectors are dirty.

 

I run on LPG or gas. Both have different injectors (two different systems), and on both problem accures.

 

throttle kick down cable on the auto tranny makeing the engine stumble???.....

else start swaping the TPS and VAF with a buddies that doesnt have the problem.

 

Glina, are you overheating at all? Does this problem happen if you drive right away with the engine being cold? Or does it happen after you have driven a while?

What are your emissions controls like in Poland? Are they any different than ours? Can you see if you have a BPMV as a part of the EGR system? (Back pressure modulation valve)

 

It is manual and cable is ok.
I don't have any possibility to change TPS or MAF, becouse 4Runners are rare in Poland and I live in Suwalszczyzna - it's a place you would call Alaska (I'm a forester).
I've mesured them with ohmometer, and these are fine.

I don't overheat. HG is cool - checked oil and coolant - my Yota steams only when it is cold and wet outside after nigth. Heater and AC works fine.

It happens only on warm or hot engine so I think it's runnig lean. Egr work well I suppouse becouse if I suck the vacuum hose that goes to Egr engine stalls, anyway idle is superb so Egr must be fine or maybe I'm wrong.

 

what about a bad o2 sensor or the cat clogging?

 

Glina; Sounds like a not fun problem. How frequently does this happen? And does the frequency vary as a function of speed? Also, no backfire, right?

 

I get no codes from ECU so i assume the O2 sensor is ok, cat is not clogged.

It's no fun at all. When it began to happen it was rare, now it's happening all the time, it happens when engine hot or warm below 3000RPM - above it's cool. There is no backfire (I had backfire once -changing wires solved the problem).

 

Glina, I'm going to assume you don't have a BPMV or whole shot valve as they used to be called. If the vehicle only has symptoms when it's hot I'd look at items affected by heat. I'd pay particular attention to anything that will effect a change on your fuel trim. Take a look at any TVVs (thermal vacuum valves).

I'd also carefully inspect any and all vacuum lines, intake manifold, etc. for leaks. It seems to me from your description that something is interfereing with your fuel trim. This is of course an assumption that you've throughly inspected and verified the performance of your ignition system.

 

Do I have any TVV? If I do where to look?

 

I can think of one. It connects to the coolant bypass outlet. The bypass outlet is bolted on to the rear of the intake manifold (hidden by the plenum). This particular TVV has two hoses coming off of it. One goes to the charcoal canister, the other goes to the throttle body.

 

I know about that one. It's responsible only for fuel system and tank pressure. I think it has something to do with air.

Could vacuum leak cause so much troubles? If so, how to find it if I've changed all vacuum lines already?

 

CL; Any idea how or what that valve does? I'm guessing (EE type here) that the heat from the coolant, at some point, provides (or not) a vacuum input to the TB? What might that be doing? And does it act like a switch, meaning totally on or off, or is their an inbetween partial vacuum condition?

Its just me right? Everybody else understands this stuff, right?

 

You're on the right track. A thermal vacuum valve is a device that allows a vacuum based upon coolant temperature. There is a little wax pellet that essentially melts at a specified temperature, allowing a loop to be created... in this case from the TB (vacuum source) to the charcoal canister for EVAP emissions control. This would a non variable type of function. It's either on or off.