birdiejim

I have a 91 4 Runner 3.0 that is running rough. The heads were redone, new timing belt components, new vacuum hoses, new water pump, new spark plugs, wires, cap and rotor. And she still working shakes like a bat out if he'll. Wont idle and when it does, runs really rough and then stalls dies. Does anyone have any suggestions?one more thing,the previous owner put a universal O2 sensor,could that b my problem?

93toyrunner2

Have you pulled codes?

birdiejim

Yes we did,no codes. Im puzzled.

sb5walker

Does it run okay when first started then start rough running after the engine reaches operating temp? Because the computer doesn't use the O2 sensor at all until the ECT reports op temp. If it runs okay, then badly, it could be the sensor - the best is the stock Denso direct fit, though a NGK (NTK) direct-fit would work okay too. Although if the PO foolishly put a universal on there, he/she may have cut the stock connector off, and that could also be the source of problems since the O2 sensor signal voltage is so low (under a volt) that any issues with the connection could introduce resistance that could lower the volts which would give the ecu a lean signal (under .45 volts), even if the O2 sensor were trying to report a rich signal (.5 to .9 volt). If that's happening the motor would run over rich and plugs would be flat black.

But if it runs badly at startup, then it's unlikely to be an O2 sensor issue and you need to look at mechanical, spark and fuel. You might add a category of EFI sensors/connections, since that could be a root cause of a fuel or spark problem.

Did it run badly immediately after the rebuild? If so, mechanical might be an issue. If compression is okay, how sure are you that neither cam pulley is off a tooth on the timing belt? Have you double-checked distrib timing? Were valve adjustments checked before it was buttoned up?

If mechanical and spark timing are okay, I'd check signals from the critical sensors at the ecu. The reason for doing that instead of checking resistance specs at the sensors themselves is that checking volts at the ecu also verifies the connections. Specs are in the Engine - MFI System - Troubleshooting chapter of the fsm. Use backprobe adapters with your multimeter if you have them; otherwise you can push needles into the connectors and hold the test leads against those.

There are specs for ignition on not running, and also some running idle and running 3000 rpm specs. On the air meter signal (VS), there are specs for ignition on not running vane closed, and vane fully open, as well as specs for running at idle and at 3k rpm.

Likewise on the throttle position signal (VTA), there are specs for ignition on not running throttle fully closed, and also throttle fully open. The reference to defeating the throttle opener you can probably ignore; I think that was added to the throttle body in 92 or 93.

Also be sure to verify the ECT by checking THW volts when motor is at op temp.

Here are specs for 92-95 trucks. I don't have my 89 manual handy, but I think the voltage specs on the 89-91 3VZEs are very close (and probably close enough to find a problem) to the later engine specs:
http://www.ncttora.com/fsm/1993/engine/86troubles.pdf

The other issue is that your ecu terminal locations may be different than the maps shown in the later years fsm. If you can't find a terminal map for your ecu, you can probably find the terminals by wire color. Fortunately, Toyota kept the same wire colors for most leads across the different years and between 4runners and pickups. Here are wire colors for 90-95 4runners:
http://www.ncttora.com/fsm/1990-1995...emci/eng3r.pdf

Assuming all the ecu to sensor connections are okay and all sensors test okay, then it's probably either a fuel pressure/injector issue or a bad coil or other spark delivery issue. I would first pull plugs and see what conditions are like inside the cyls. Black deposits mean rich running, possibly weak spark, white deposits indicate a fuel starvation issue, either low fuel press or clogged injector.

Check the resistance of both circuits in the coil, using hot specs (when motor hot, of course):
http://www.ncttora.com/fsm/1993/ignition/12onvehicl.pdf
Disconnect all wires from coil before testing. Primary circuit is between positive & negative terminals; secondary is checked between positive terminal and the high volt cable terminal (that connects to distributor).

Make sure the high volt lead from coil to distrib is not shorting out on anything, and make sure distrib cap & rotor are in good shape (especially check terminals inside cap), and make sure the wires and plugs are good.

For fuel, could be tired pump, clogged fuel filter, bad press regulator, or clogged injectors. Make sure the vacuum lead to the top of the press regulator is the one from the fuel pressure vsv and does not have vacuum when motor is above idle. Fuel pressure specs here:
http://www.ncttora.com/fsm/1993/engine/87fuelpump.pdf

Fuel pressure VSV troubleshooting here:
http://www.ncttora.com/fsm/1993/engine/99fuelp.pdf

Pressure regulator replacement procedures here:
http://www.ncttora.com/fsm/1993/engine/89fuelpres.pdf

If fuel pressure okay and plugs show lean, probably clogged injectors. Send 'em to witchhunter.com.

Good luck!

barrell319@yahoo.com

i own a 91 4runner it runs great up until its warm then the idle drops to 500rpms and eventually it dies.then it wont start for about 30 to35 minutes i was thinking its the fuel pump or the filter but im reading this site and starting to think its more than that! anyone know or have a clue what it is causing the issue? Im stumped and really need some help!!! thanks also i had the injectors checked there fine.im reading this and im wondering could or can the o2 sensor maybe be the problem im having? or do you think its the press regulator?

93toyrunner2

Keep reading, use the search button above, and also download the FSM from the link in my signature. Do something called "diagnostics", get codes, and also, the motor size is important. Oh, and how did you have your fuel injectors tested?
Spark Plugs (are they OEM types mentioned in the FSM? Is the gap set correct, or did you just put them in?)
Plug wires.
Cap
Rotor
Timing
Fuel filter
Air Filter
Fuel Pump
Vacuum leak
Leak in the air intake system, cracks in the intake hose
Fuel injectors misfiring, clogged, not even flow
Cold Start Injector
Cold Start Injector temperature sensor
Bad Gas
Fuel Pressure regulator
VAF
ECm
O2
EGR
Throttle Body
Dash POT
Idle Speed adjustment
Flooding, check plugs for gas.
Cylinder compression test.
Just to name a few things off the top of my head.

barrell319@yahoo.com

my best friend owns a shop and owed me a favor.otherwise would have been about 400 dollars

93toyrunner2

What!?!

barrell319@yahoo.com

yea im in iowa its not cheap but i've only had the truck for about a month i've bought new exhaust,tires,brakes,tune up,shocks. bad thing is i only paid 900 for the truck but i'm not willing to part with it. thats my go play in the woods truck and the sad thing is thats all i do with it. but if i can get this problem figured out maybe she'll get more love from me and ill drive her alot more on the road!! the owners before me didn't take care of it very well everything on it is factory from the day it was made so something small like changing shocks is a really big task because its been there so long!

93toyrunner2

You can go through the list I mentioned above, and replace 1 thing at a time, hit or miss, and spend hundreds more, or, you can download the Factory Service Manual, and open the diagnostic section, and figure out what is wrong with the truck. There is nobody on this site that can tell you what is wrong with the truck unless we have more information.

barrell319@yahoo.com

hey you have helped out alot that manual should lead me in the right direction. i just hope it isn't the regulator i dont want to mess with the fuel injection. but we will see

Rhodes89

Same trouble with my 3vz look and looked still cant figure it out

Cambamalam

I have had the same problems, full tune-up, replaced sensors, but my 95 4runner just ate through its second VAF, this is the most plausible cause of the bad idle ( if you can start it).

I checked the newer one i had just gotten and the resistance of the two bronzish tabs(Forgot terminal names) on the right should read over 200 ohms, and under 600. if not, replace it.Did head gaskets w/ resurface, water pump, cams, spark, rotor, cap, spark cables, air filter, air intake hose, 02 sensor,, new vaccuum lines, cleaned out all the VSV switches (can get stuck )