BarrettK

Ok so I have a 1990 4runner 3.0 3vze Auto.

My car is stalling from dead stop, getting 10-12 mpg and feels terrible on the road as it feels like it is barely chugging along.

What I have done to try and troubleshoot the problem:

Fuel Filter
Spark plugs/ Wires
O2 Sensor
Airfilter
Fuel injector cleaner
Alternator
Distributor cap and Rotor
New/ calibrated TPS
...
...
Low compression on 2 cylinders
...
...
...
Rebuild
New piston rings
Machined the heads (3 valves were leaking bad and head gasket was partially blown)
Valve Job
Water pump
Timing belt
Various rebuild parts ect.
Checked for vacuum leaks
...
...
3 oil changes and 500 miles later.
I am having the same problems again.
Checked the coil and I get .4-.5 ohms

I have put too much money to give up now, but I am at the end of what I can do.

I get 1 code that says the TPS is off, but I know it is properly calibrated as I have checked it 3 times. I was getting the same code before the rebuild.
Weird thing is if I unplug the battery or take out the EFI fuse the car runs "better" as it does not stall, but it will start having problems again the next day.

Any help would be greatly appreciated.
Thanks

BarrettK

Could it be a bad ecu/ short in the wiring? Fuel pump? Does anyone have any idea?

Co_94_PU

iTrader: (-1)

You get code 41 right? That's "Open or short detected in throttle position
sensor signal (VTA) for 500 msec. or more"

Lets assume your TPS is properly adjusted and functional. That leaves only bad wiring or a faulty computer. Could be as simple as a dirty pigtail/plug, or the plug at the computer is loose.

Perform the tests, inspect for damaged wires and clean the connectors.

BarrettK

I cleaned the connectors. I connected the ohm meter to Idl -E2 and with the throttle closed and it reads .355 M-ohms. When I open the throttle it reads .355 M-ohms. So i disconnected the TPS. .354 M-ohms.

Vta -E2 reads within spec.

Just to make sure... the the wiring harness is to be disconnected from the ECM when I am checking the wiring correct?

I did not check the voltages because I cannot get the probes into the wiring harness with the connectors plugged in. There is no room. Can I unbolt the ECM from the kick panel and ground it with a wire and then check it?

Co_94_PU

iTrader: (-1)

Is that milli-ohms or Mega-ohm, just to be clear?
Not really relevent since it should be Open, eg. no connection between IDL and E2 with the throttle open. Just to be sure unplug the computer and sensor, and test that IDL line vs a body ground at either end. If it is shorted out you might be able to get a since of where it'ss shorted by testing both ends, the one with the least resistance is closer to the short.

Try wiggling the harness and see if you get fluctuations or a disconnect, since this is where you should have found the problem. As the error code indicated.

Yes, disconnect the computer and test the harness side of the connection, not the computer.

The case ground is generally just for noise isolation, but not a bad idea to make sure it's grounded to prevent ESD(electro static discharge) damage.

You don't really need to do the voltage tests, the resistance check already indicate there is something wrong in the harness.

BarrettK

The M-ohms is Mega.

I'll get a buddy to look at it with me tomorrow and try find a short.
I'll keep you updated.
Thanks

BarrettK

Ok so I'm not sure what was up with the readings the other day, but when I just checked it here is what I got.

Vta-E2 at TPS with throttle closed = 1.01 k-ohms (.47-6.1 is spec.)
Vta-E2 at ECM connector throttle closed = 0.0307 k-ohms
Vta E2 at TPS throttle open = 4.47 k-ohms (3.1-12.1 is spec.)
Vta-E2 at EMC connector throttle open = no continuity

So guess there is a short in the Vta wire somewhere. The easiest thing to do would probably be to run a new wire for Vta. What do you think?

Co_94_PU

iTrader: (-1)

The reading difference is because its a damaged wire

yeah probably. I'd tell you to just replace that whole part/section of the wiring loom if it was a 4-cylinder, since there is plenty of room and it's easy to get to. It's only a little bit harder for the v6.

First thing to do would be see if it's something simple like damage at the connector, then you don't have to fish any wires just the plug. Plus if you reuse the plug and it's the problem your not gonna be fixed

BarrettK

ha ah yes.

Well i'll give it a shot and see what happens.

I also am not sure why the value for Idl-E2 does not change when the throttle is open or closed. I was looking at the wiring schematic link and it does not look like it splits and goes anywhere else. If I do end up running new wire for Vta I will probably run new wire for Idl too.

Co_94_PU

iTrader: (-1)

Needs adjusted or it's broke and needs replaced.

BarrettK

Wow... what a difference. I went ahead and replaced both Idl and Vta from the connector at the TPS to the connector at the ECM.

Thanks you so much for your input. Can't wait to run a tank of gas and check the MPG, but it feels so much smoother.