STUMPED! Rough idle and low power issue- HELP!

[jordancollard97]

At the end of my rope, this is the last ditch effort before I haul it to the dealer!

1994 FZJ80.

This issue only occurs when the vehicle has sat for more than about 30 minutes.
Upon cranking- very rough idle. Then when driving, slow acceleration, low power, surging, etc.
Then, all of a sudden after a couple of minutes of driving, it’s as if the engine literally comes to life!
There’s a big surge of power, and the vehicle is running perfectly fine.

I can’t stress it enough- in a split second it will go from sputtering like it’s about to die to running and idling totally normally.

I have replaced the VAFsensor, O2 sensors, cleaned PVC valve, cleaned IAC valve, checked the timing, nothing has really worked.

Only code that is showing is code 26, but I’ve had that code, intermittently for a while

Any ideas?

 

[ChaseTruck]

Vacuum leak that self-closes when things get up to operating temps?

 

[jordancollard97]

Vacuum leak that self-closes when things get up to operating temps?

Someone else said this…

I’ve tried my best to check all the hoses and can’t find them.
But a vacuum leak makes sense!!!

 

[voodu3]

I think the code 26 could be your issue

 

[mrsleeve]

My 1st thought is a sluggish or lazy temp sensor for the computer.

 

[bigredmachine]

check the wiring for the o2 sensors, mine had rubbed through on one of them causing similar issues. po had done a fairly ok job at the repair but there was corrosion getting into the wires so i redid the repair and it was fine after that

 

[jordancollard97]

OK, everyone, update.

I climbed under the cruiser and unplugged the oxygen sensors. Both of the connectors, but especially the one on the outside were corroded and watery.

I cranked the truck, and it idle more smoothly than it did when they were plugged in.

I’m thinking, clean the connectors with electrical cleaner, and a touch of dielectric grease. Yes?

 

[bigredmachine]

cleaning the pins is a good start but depending on how corroded they are you may want to get a new connecter with pins and splice them in

 

[BILT4ME]

OK, everyone, update.

I climbed under the cruiser and unplugged the oxygen sensors. Both of the connectors, but especially the one on the outside were corroded and watery.

I cranked the truck, and it idle more smoothly than it did when they were plugged in.

I’m thinking, clean the connectors with electrical cleaner, and a touch of dielectric grease. Yes?

There are two temp sensors on the engine. One for the gauge, one for the ECM.

If the sensor for the ECM is having an issue, the ECM is not seeing the correct temp. During a cold start, the ECM places more fuel into the system and changes the voltage to the fuel pump and holds the injectors open slightly longer for a rich condition. This is open loop.

once the engine is up to operating temp, it goes into closed loop and it will change speed on the fuel pump and shorten the duration on the injectors to lean out the mix for a better air /fuel ratio.

If there is an issue with the temp sensor, it may be giving you too much fuel at the wrong time, causing a rich condition, and thus a code 26.

 

[jordancollard97]

There are two temp sensors on the engine. One for the gauge, one for the ECM.

If the sensor for the ECM is having an issue, the ECM is not seeing the correct temp. During a cold start, the ECM places more fuel into the system and changes the voltage to the fuel pump and holds the injectors open slightly longer for a rich condition. This is open loop.

once the engine is up to operating temp, it goes into closed loop and it will change speed on the fuel pump and shorten the duration on the injectors to lean out the mix for a better air /fuel ratio.

If there is an issue with the temp sensor, it may be giving you too much fuel at the wrong time, causing a rich condition, and thus a code 26.

You don’t have a link for this temp sensor do you? I’m trying to look, and having trouble differentiating the two different sensors.

 

[jordancollard97]

My 1st thought is a sluggish or lazy temp sensor for the computer.

Do you have a link for the sensor? Having trouble finding it

 

[BILT4ME]

You don’t have a link for this temp sensor do you? I’m trying to look, and having trouble differentiating the two different sensors.

You need to plug in your VIN. This is for my 1996.

https://partsouq.com/en/catalog/genuine/unit?c=Toyota&ssd=%24%2AKwGWorOo-9PS1u3glce0kM7a-v3j2svi29-HzZ6H-IGIh8GCx8eS2tDLx-TegMOUl82ekY6BwszGgsfR15CVk4GIh8vO38nNnJGUm5CTgN2DhYbA5dmBx8aAmt3R2J2UlpeUh46A35qbhp-CgfTk8OGw0cOEh8_Ahp-CgruppZyV7o7j6_LltrLNiIWA1ceHmICThoPIiYKBwszGgsfT3dkAAAAAXzNGCg%3D%3D%24&vid=0&cid=4&uid=416044&q=

 

[DIRTBIKEUSA]

If it’s not diagnosed yet. I say Fuel pressure regulator may be bad?

 

[CharlieS]

There are two temp sensors on the engine. One for the gauge, one for the ECM.

If the sensor for the ECM is having an issue, the ECM is not seeing the correct temp. During a cold start, the ECM places more fuel into the system and changes the voltage to the fuel pump and holds the injectors open slightly longer for a rich condition. This is open loop.

once the engine is up to operating temp, it goes into closed loop and it will change speed on the fuel pump and shorten the duration on the injectors to lean out the mix for a better air /fuel ratio.

If there is an issue with the temp sensor, it may be giving you too much fuel at the wrong time, causing a rich condition, and thus a code 26.

I think there are three, those two plus the AC high temp cutoff sensor.

Good visual here:

Engine Coolant Temp. Sensor

I installed an UltraGauge. It has to have OBDII to work though, so limited to some 95, and 96 and 97 trucks. I have an alarm set so it beeps at temperatures over 200 degrees F. And, it tells you what the computer is seeing so you know the health of your sending unit. I consider it a well spent...

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