Any Ideas? Irregular idle, jumping at speed

[dannyvp]

Bad Idle

https://youtube.com/shorts/L5O7dRKa7d4?si=fHXAuDkIT5ByaXpF
Maybe this video will work.
92 80 series, 3FE
At speed 40-50 MPH idle jumps around a lot. Massive jumps as seen in the video.
No visible cracks in vacuum lines, no major changes in system.

Ideas? Looking at the FSM now.

 

[dannyvp]

After testdrive heres what i noticed. This happens while under more than half throttle, not sunday cruising it seems.
The CEL blinks on in large jumps. Basically a single flash.
Could this be injector problems?

 

[dannyvp]

Any ideas? I’m going to work on this some for my son.
I was thinking about getting a new TPS and cleaning the throttle body as well as checking the air flow sensor.

Would you call the video “ruff idle”?

 

[jonheld]

After testdrive heres what i noticed. This happens while under more than half throttle, not sunday cruising it seems.
The CEL blinks on in large jumps. Basically a single flash.
Could this be injector problems?

The CEL flashes because the engine is stalling, not because of an error code.
I would be looking at the EFI system. EFI main relay and associated circuits, coil/igniter, etc.
The fact that is happens under load suggests that when the engine shifts on the mounts, a connector or wire is moving causing the issue.
A bit of percussive diagnosis with the engine running will likely illuminate the issue.

 

[dannyvp]

What do you mean by percussive?
I have tested by reving the engine while testing and have seen or heard nothing other than an loud 3FE running.

He has been having EFI relay issues and I was going to move it into the cabin.

 

[DIRTBIKEUSA]

I dont want to say it but is the transmission slipping?

 

[dannyvp]

I dont want to say it but is the transmission slipping?

I wonder that when I first heard about this, but I don’t think so after driving it. I don’t feel a hard shifting or anything, just see the RPM’s raise and drop.

 

[DIRTBIKEUSA]

I wonder that when I first heard about this, but I don’t think so after driving it. I don’t feel a hard shifting or anything, just see the RPM’s raise and drop.

Have you serviced the trans? How’s the fluid look smeared on white paper? Does it smell burned? Does it feel gritty between your fingers? Right level cold AND hot?

Even if it’s not a trans issue, bouncing RPM under load can cause wear in the clutches..

 

[dannyvp]

Have you serviced the trans? How’s the fluid look smeared on white paper? Does it smell burned? Does it feel gritty between your fingers? Right level cold AND hot?

Even if it’s not a trans issue, bouncing RPM under load can cause wear in the clutches..

We changed the fluid when we got the truck, but that was it.
Probably time for it to be serviced also.

 

[DIRTBIKEUSA]

We changed the fluid when we got the truck, but that was it.
Probably time for it to be serviced also.

Did you put in a new filter? Maybe cork gasket on old filter isn’t sealing and is sucking air in from inside the pan when the trans demands higher flow? Not external, internal..

 

[dannyvp]

Did you put in a new filter? Maybe cork gasket on old filter isn’t sealing and is sucking air in from inside the pan when the trans demands higher flow? Not external, internal..

No we did not.

 

[DIRTBIKEUSA]

First check trans fluid level and quality and quantity hot and cold. Then service the trans with a new filter. Make sure to inspect old filter. Post up some pictures of you are unsure.

Also it might be a good time to drop the shift solenoids and inspect and clean them out.. I believe you should not be able blow through them with lung power. That’s how I test them..maybe someone has a better way..also inspect change out old solenoid seal orings.

If this isn’t the problem at least you have properly serviced the trans and eliminated it as the cause.

 

[LandCruisinMy93]

@dannyvp Percussive maintenance is the technical term for hitting stuff to make it work.

Like giving a stuck starter or a dying alternator a whack to free up brushes.

 

[jonheld]

What do you mean by percussive?
I have tested by reving the engine while testing and have seen or heard nothing other than an loud 3FE running.

He has been having EFI relay issues and I was going to move it into the cabin.

I would be willing to bet that this is an electrical issue. A slipping transmission would not cause the engine to stall.
Also the pick up filter in the transmission pan is a steel mesh and can simply be cleaned. No need to replace it unless damaged.

Percussive diagnostics: with the engine idling in your driveway, start moving wire harnesses around. Start wiggling connectors. If you've been having trouble with the EFI relay, maybe the socket(s) are faulty.
Maybe the fusible links are failing from fatigue.
There are quite a few possibilities here for an intermittent issue.