I have recently completed a 3.4 swap into my 4runner, the motor is running great, aside from the idle and WOT, and fuel mileage. Here is some basic info on my swap.

-My truck, 1990 4runner SR5 3.0 manual
-3.4 engine is from 1998 4runner federal emissions
-Wiring harness and computer is from 2000 4runner 4x4 Auto, California emissions.


I am getting about 8-10 MPG, running extremely rich, idles between 1500-1800 RPM once it is warmed up. When it is cold it idles around 1200, and slightly rough.

It has great power at 25% throttle, but once I push the pedal in more than about half way it bogs down and loses all power. As soon as i release the gas pedal it picks up again, and runs great. I am getting code p0171, and a few transmission codes of course.

I have a few friends with these engines, so I have been able to swap parts back and forth to track this issue down, so far I have swapped out or replaced....

-Air flow meter
-Throttle body with TPS, and IAC
-Brand new Denso A\F ratio sensor
-Coolant temp sensor functions normal according (174ish degrees)
-Checked for vacuum leaks with starting fluid, smoke test, and visual. No leaks
-Checked for exhaust leaks before the first o2 sensor, none.

The truck runs the same whether it is in closed loop or open loop, so it cant be an o2 sensor issue. I have not been able to check fuel pressure because I do not have the adapter to do so, although my 3.0 ran fine before I pulled it. And I do not think fuel pressure could have this big of an effect on the engine, and cause it to idle high, as well as run rich.

I appreciate any and all help, this problem has been getting the best of me! By the way, this swap was extremely easy to do otherwise and I encourage anyone who is considering doing it to do so. I got a lot of misleading, and just plain bad advice from reading forums before doing my swap. My entire swap from start to finish cost me $440, including the engine!! (which I got for free with a blown headgasket) I will post my entire cost breakdown as well as parts that ARE re-usable from your 3.0

-3.4 engine, FREE
-Headgasket set, headbolts, and machine work $220
-Spark plugs $20
-Wiring harness with computer (auto harness) $80
-Evap box from 3.4 $40
-3.4 power steering pump $40
-Misc fuel return line and vacuum lines $20
-Air Flow Meter $20

3.0 parts I used for my swap
-Flywheel
-Clutch
-motor mounts
-Oil pan (you DO NOT need a T100 oil pan on a SAS toyota!)
-Oil pan pick up tube (used 3.4 baffle, cut a small hole for dipstick tube)

Now back to the original post, why is my 3.4 running like this??

 

Normal operating range temp is 174-203F per the FSM with a 180F t-stat. Running too cool will cause a high idle.

 

remove the throttle cable then run it. Most people dont realize the cable is too tight and hold the throttle open. Do the sensors on the motor match the 2000 ecu? What plugs are you using?

 

The coolant temp was registering 174 after I had parked the truck, and hooked up my scan tool. I watched the temp rise beyond 174, as well as taking a temp reading first thing in the morning and watching it rise.

I have tried leaving the cable off on two different throttle bodies, as well as pulling it towards the closed position, pushing it sideways etc. the throttle plate is sealing well.

The AF Ratio sensor I bought is for a 2000 4runner with california emissions. I have ran the part numbers for the throttle position sensor, IAC, and AFM. They all show the same part for the 1998 federal emissions 4runners, as well as the 2000 cali emissions 4runners.

Thanks for the replys so far!

 

Sorry forgot about the spark plug question, I am using NGK iridium double electrode type. Just like the OEM Denso plugs

 

did you get the vent line and the return line mixed up? is the FPR getting vacuum?

 

I have the FPR hooked onto a port on the intake manifold getting vacuum, I recall reading on another forum that the FPR is actually supposed to be routed to the intake without getting vacuum. I have tried both ways, and made no change.

That is a very good idea about the return line being hooked onto the vent line! Thank you for that, I will check that asap tomorrow morning.

 

The big problems I had was AFM and SPEED SENSOR.

- For some reason I cannot run the newer style AFM. So, I still run the old style and clean it every oil change.
- I had to swap the speed sensor out and that made all the difference.

Just a few thoughts!

 

Heres an update, unfortunately.... My FPR is hooked up correctly and getting vacuum, as well as my return and vent lines.

I did not know there was a "newer" style AFM, the AFM I have in my truck is from a 1998. However, an AFM meter I borrowed from a friend was out of the same truck I got my harness and ECU from and that made no change.

My truck does not have a speed sensor, the speedo is cable and there is no abs. Can a speed sensor cause the engine to run like this? I also have a cold air intake on my swap, I have not tried swapping it out for a stock airbox but im not sure that could be causing this big of an issue or not, I have the AFM pointing the right direction.

 

Trust me, you have a speed sensor. My '86 does. It's directly behind the speedometer.

 

Thanks for that information! According to Alldata it looks like the sensor takes the mechanical signal and converts it to an electronic signal for the ecu, that seems odd to me since my truck was a 5-speed from the factory. I'll go ahead and review the diagrams and splice that sensor in tomorrow afternoon.

Did you have similar issues when your speed sensor was not hooked up?

 

Well I basically lost my ability to get my cruise control to work. The ECU takes a direct signal from the speed sensor. It definitely helped my juank run better.

 

That is correct, converts mechanical to electrical. I didn't have mine hooked up for a little bit and the motor ran fine but threw a code. I would look hard at that "cold air" intake. Swap on a factory box if possible to rule that out.

 

Another update.. I have the speed sensor hooked up now, made no difference. I have also swapped on the factory intake system from the 3.4 with yet again, another AFM. No change. Im open to all suggestions, if I cant figure it out over the next few days Im going to buy a harness and ECU from a 98 4runner, and start all over again :/

 

do you know if the tps has to be from a 4wd if your truck is 4wd? how important is the tps when it comes to the driveline?
thanks