94yota4rnr

This is my first post but i'm a long time lurker. I just rebuilt my 94 3.slow and all has gone well but now i got the engine shakes at idle and when i'm holding speed constant going down the road. I got rid of crossover with LCE headers and performance is good. It doesn't shake when i first crank it up in the mornings or when the motor is cool.
I would like to thank everyone here on this forum for the help this past year. If i needed an answer i just searched this site and found the answers i needed. Now i'm stuck and need help.
I will post pics as soon as i find out how.
Thanks,
94yota4rnr

thook

Golly........that could be a number of things. Read this troubleshooting guide and see if ol' inuition sparks at any of the possibilities. Your probably looking at rough idle and hesitation/poor acceleration.

First thing that comes to mind for me, though, is the coolant temp sensor. Does it seem to run especially rich once warm (note any strong fuel odor from exhaust)? Possibly the sensor not responding well to coolant temp change and the ECU believes the engine is still cold and injecting more fuel than necessary at operating temp. Check the connector first. Make sure there' nothing wrong with the wiring.

Sensor location.....
https://www.yotatech.com/forums/f116...cation-154218/

Then, there's the oxygen sensor. How old is it, and does it have a good connection?

94yota4rnr

i reset the ecu and while it was down i took the new o2 sensor out and cleaned it. When i cranked it back up it ran Great and then the CEL came on (code 25). After rebuid I replaced Tps, o2 sensor, knock sensor and pigtail. Now when i reset the ecu, it runs great til i come to the first red light or stop sign and it idles for a minute then CEL light comes on and code 25.
thanks,

94yota4rnr

thook

Oops......I didn't post the troubleshooting link above:

http://personal.utulsa.edu/~nathan-b...63troubles.pdf

Code 25 means a lean condition. A vehicle could be running lean, but the ECU could still compensate for it by enrichening the fuel mix (by keeping the injectors open longer) and you would still not get a code. However, normally when a code (eg, lean) appears it's because the condition is so lean the ECU can't compensate keeping the a/f ratio at an average of 14.7 parts air to 1 part fuel......it's staying too long on the lean side. BUT! You said you cleaned the O2. What'd you use? Things like brake cleaner, TB cleaner, etc. can damage the sensor.

94yota4rnr

Thanks thook,
Sorry about delay in responding, got called out of town for work.
This problem is getting the best of me. I cleaned the o2 with o2 safe electric cleaner. I have reset Tps, timing and pulled front of engine off to make sure belt timing is correct. Nothing seemed to help.
When i started this project i brought a 90 4runner to rob parts from. I took the mafm off 90 and installed on 94 and the Code 25 has gone away.
The shaking at cruise speed is at every speed i have tried to maintain when going down the road. It doesn't shake during acceleration or decelaration and it has power when you stomp the accelerator. It still shakes at idle after it warms up. I'm starting to think I have an injector problem.
again thanks,

94yota4rnr

thook

What makes you think it's an injector problem? Do you know if the idle air valve is working right?

94yota4rnr

How do i check the idle air valve and does it affect or cure the shaking at Rpms at cruise speeds (2250 at 55 mph) or at rpms like 25 or 35 mph. I dont feel it shaking unless i am trying to hold a constant rpm or speed going down the road or at idle at a red light or stop sign.
Also i have been troubleshoting and i have found that the idle speed isn't going up when i turn on the ac.
Thanks,
94yota4rnr

thook

You said it was shaking at idle after warm up. So, that's why I asked about the idle air valve. It's just something to rule out, simple as it is to test. There could be more than one thing going on, so it's good to start out with some simple things. Another thing that comes to mind is possibly the fuel pressure regulator. That would have more of effect while driving and could be cause for any O2 codes.

So, to check the idle air valve, mark where your idle adjust screw is currently. Start the vehicle and turn the idle adjust inward all the way counting how many times you pass your mark. While the motor is cold, the idle should drop a bit. Then, once the engine is warm, turn the idle adjust inwards again. The engine should die or just about.

For the fuel pressure regulator, pull the vac line off and see if there's any fuel in it or if it even smells like fuel. If there is, it's bad. Also note the change in engine speed. The RPM's should go up. If there's no change, the regulator is most likely bad.

94yota4rnr

Thanks thook,
I just did the idle air and when i turned it in cold the idle dropped a little bit, when i turned it in warm it just about died.
As for the pressure reg i took the vacuum hose off and no change in rpm. When i held a screwdriver up to the reg and put the other end up to my ear, there is constant ticking.
Thanks for all your help i guess im gonna change out the reg.


Thanks again,
94yota4rnr

94yota4rnr

I'm looking for help on finding the air valve on my 94 v-6. I have replaced the fuel pressure reg and the coolant thermo switch and i am still getting code 25.
I bought a Haynes repair book on the 4runner and it says the rpm shouldn't drop when I turned the air idle valve in hot. I guess this is my next route in repairs.
thanks for any help,
94yota4rnr