Rough idle and low power issue- STUMPED!!! (1 Viewer)

[jordancollard97]

Definitely frustrated. Last ditch effort before hauling it to the dealer.
1994 FZJ80.

The issue only appears when the vehicle has sat for a little bit, more than 30 minutes.
Upon cranking, the idle is VERY rough. When trying to accelerate, there is low power, surging, etc.
After driving for a few minutes, literally all of a sudden, I can feel the engine return to normal. Huge surge of power. And all of a sudden it’s driving fine! Then it will drive and idle fine to the next time I park it and leave it sitting.
Then it all starts over.

I can’t stress it enough, it will literally go from feeling like it’s about to sputter out and die, to driving perfectly fine in one split second.

Only code that’s been thrown code 26. But I’ve had this code intermittently for a while.

O2 sensors replaced, VAF replaced, IAC valve cleaned, PCV valves cleaned, timing checked, vacuum lines checked. Etc.

Any advice at all? Please help.

 

[Fj80oregon]

A dealer will be worthless, find a local competent Land Cruiser shop or maybe we can help out here. Your O2 sensor is a common issue here did you replace with a quality brand. Have you tried running it with one unplugged or both unplugged? Are the connectors in good shape cleaned out with electrical terminal cleaner. Do you have a FSM to run diagnostics on the O2’s?

 

[BILT4ME]

There are more responses in his other thread. Go look there and don't post here.

 

[hbange97]

A dealer will be worthless, find a local competent Land Cruiser shop or maybe we can help out here. Your O2 sensor is a common issue here did you replace with a quality brand. Have you tried running it with one unplugged or both unplugged? Are the connectors in good shape cleaned out with electrical terminal cleaner. Do you have a FSM to run diagnostics on the O2’s?

I am having similiar issues - low/rough idle comes on randomly. Ordered some new O2 sensors but would like to test the old ones first by disconnecting. Is there any risk of damage by running with both O2 sensor disconnected over a few days or so? Only because the issues comes and goes but is frequent enough to need addressing.

 

[BILT4ME]

I am having similiar issues - low/rough idle comes on randomly. Ordered some new O2 sensors but would like to test the old ones first by disconnecting. Is there any risk of damage by running with both O2 sensor disconnected over a few days or so? Only because the issues comes and goes but is frequent enough to need addressing.

Is your truck OBD2?

If so, get a reader like UltraGauge and watch the readings on the O2 while driving.

Running with O2 disconnected, it will drink the fuel. You may end up with more codes. but, will it "hurt" it? No.

You can also pull the main fuse (ECM?) in the fuse block for about 60 seconds and it will clear existing settings and may help clear up issues. It's like disconnecting the battery.

 

[jordancollard97]

I am having similiar issues - low/rough idle comes on randomly. Ordered some new O2 sensors but would like to test the old ones first by disconnecting. Is there any risk of damage by running with both O2 sensor disconnected over a few days or so? Only because the issues comes and goes but is frequent enough to need addressing.

Not necessarily a risk of damaging if it’s only a couple of days.

If you do it for long, it won’t be great for your system.

By the way, the resolved issue turned out to be the Air Flow Meter

 

[hbange97]

Any tips for removing old O2 sensor? Nut is completely rusted over..

 

[BILT4ME]

Any tips for removing old O2 sensor? Nut is completely rusted over..View attachment 3712456

Soak with PB Blaster for about a week. Or an ATF and acetone mix.

Using a tiny hammer, smack the nut on as many sides as you can reach without damaging the threads of the studs. The vibration helps break them loose.

Then use small vise grips and unscrew the nuts. If that doesn't work get a nut splitter from FLAPS and split the nut but be careful to not score the threads on the studs.

Once off, run a die over the stud threads to clean up.
Use a flat bastard file to clean up the sealing surface.

Grab new flanged nuts from FLAPS, use copper anti seize on the threads, a new gasket the or the sensor, and torque snuggly. I can't ever get a torque wrench on them, so 15 elbow-LBS.

 

[thatbrown80]

I had some intermittent power issues on my 94 and it was the VAF meter. Luckily I had a spare. VAF has some control over the fuel pump also.

 

[hbange97]

I had some intermittent power issues on my 94 and it was the VAF meter. Luckily I had a spare. VAF has some control over the fuel pump also.

Excuse my ignorance, is that the same as the MAF?

 

[AussieHJCruza]

Excuse my ignorance, is that the same as the MAF?

Equivalent function but works differently. 1995 onwards got a MAF.

 

[hbange97]

Is it worth trying to clean? See alot of people say dont touch it..

 

[AussieHJCruza]

Is it worth trying to clean? See alot of people say dont touch it..

Not really anything to clean in the way that a MAF does.
Don't remove the small screws and go pulling the wiring, this is what damages them.

 

[robnicko]

This is the only MAF cleaner ive ever used and if you do make sure you follow the instructions to the dot.
I had to use it on a car that had a uni-filter element and the oil from it played havoc with the MAF but this stuff worked a treat. Got rid of the Uni Filter after that.....

CRC Mass Air Flow Sensor Cleaner 300g

Most fuel injected vehicles are fitted with a mass air flow (MAF) sensor to measure air velocity which the computer uses to determine the proper air/fuel mixture. However, the MAF sensor gets dirty with debris, oil, grease and air filter fibres, causing inaccurate measurements of air flow which...

crcindustries.com.au

 

[robnicko]

The issue only appears when the vehicle has sat for a little bit, more than 30 minutes.
Upon cranking, the idle is VERY rough. When trying to accelerate, there is low power, surging, etc.
After driving for a few minutes, literally all of a sudden, I can feel the engine return to normal. Huge surge of power. And all of a sudden it’s driving fine! Then it will drive and idle fine to the next time I park it and leave it sitting.

also, the above does sound a bit like a faulty fuel pressure regulator especially where you state it happens after sitting for a bit

 

[jordancollard97]

Is it worth trying to clean? See alot of people say dont touch it..

99.99% of the time, if these air flow meters malfunction, it’s not because they need to be cleaned, it’s because the internal components has broke loose or melted.

 

[Malleus]

I'd use a dremel and cut those nuts off. I'm all for trying to salvage anything except exhaust fasteners; they're evil. Just exorcise them and be done with it. Do use anti-seize on the new ones though, that's what it's made for.