FJ62 Runs rough above idle

[yeahmag]

My 1988 FJ62 seems to run rough above idle - 1000 RPM to maybe 1300 RPM. It smooths out after that and is almost imperceptible when driving. This is most pronounced in neutral/park. Is this normal for these trucks or do I need to hunt down the problem(s)?

I put new plugs in not all that long ago (maybe a little over a year and it's a low mileage truck). Valves were adjusted a few years ago.

This isn't a new problem, just been doing work to the truck (long over due) and thought I'd chase this down too...

-Aaron

 

[RockDoc]

Is this just off idle? I wonder if it could be that the throttle position sensor is acting up in the transition from closed (idle) to openning (throttled). Maybe a weak return spring, or out of adjustment? Mechanically the engine is raising above idle, but the computer isn't registering it and adjusting the EFI?

That said, I'm sure someone will chime in who has dealt with the same symptoms.

 

[bull]

Have you checked your intake hoses for leaks, Cracks, etc? Check them closely for any cuts, tears, or cracks. Make sure the clamps are tight.

Do that then post up again.

 

[RockDoc]

Have you checked your intake hoses for leaks, Cracks, etc? Check them closely for any cuts, tears, or cracks. Make sure the clamps are tight.

Do that then post up again.

True that. A common issue that seems to crop up with the 3FE is the intake hose between the air cleaner and throttle body splitting along the bottom.

 

[yeahmag]

I'll check that out... I also have been sitting on a FPR to install in it as I thought (from reading the board) that it would be wise just to put a new one in. Maybe I'll do that while I'm in there.

-Aaron

 

[bull]

No. Do one thing at a time.


That way you can tell easily what the fix was.

 

[yeahmag]

OK. So I took both hoses of from the air cleaner to the TB and found a few cracks in the corrugated "elbow", but none of them were all the way through. I filled them with non hardening gasket sealer stuff. I cleaned the TB with TB cleaner and decided to go ahead with new plugs, cap, and rotor. This helped, but I still have a stumble at 1000-1200 rpm's.

I put a vacuum gauge on it and it pulled (trying to remember here) 20-25Hg. I also tested the FPR by pulling the vacuum line to it, the idle did go up. I'd guess I have to test the TPS and or mess with the "golden screw" next.

Any other things I should look for?

-Aaron

 

[yeahmag]

I forgot to mention that I poked around with my HF mechanics stethoscope and found a noisy injector. It was much louder than it's cousins. Could that be a potential problem?

 

[billmc]

I'd guess I have to test the TPS and or mess with the "golden screw" next.

Aaron, some people like to mess with the golden screw, but to my mind that's just trying to compensate for some other problem. If you do decide to alter it, you should probably mark it's original position in case you want to put it back to the factory setting. Also, one of the functions of the TPS is to signal a fuel cut to the ECU between 1000-1300 under certain conditions. Apparently they can fail such that they send that signal at the wrong time, though I don't understand exactly how. It seems to be happening a lot lately. You should definitely test your TPS according to the FSM.

Bill

 

[yeahmag]

I'm also gonna order an oil dipstick for the truck. It's *really* loose in the bore. If that's a potential vacuum leak we may have a winner...

I will check the TPS as soon as I can.

-Aaron

 

[FZJ80ismybaby]

can a loose dip stick for the oil really do that, cause mine is loose

 

[yeahmag]

I would think it would have the same affect as a loose oil filler cap. It's only $16-18 to try. It bothers me either way.

-Aaron

 

[RockDoc]

Try some electrical tape to seal it up.

 

[yeahmag]

Just a quick update...

I added a can of Seafoam to a 1/4 tank and then added an additional 10 gallons of gas (that should be about 15 gallons total on my truck) and the truck is slowly smoothing out. It actually surprised me today how smooth it was.

I didn't get the chance to Ohm out the TPS yet, but it's still on my to-do list.

-Aaron

 

[yeahmag]

Another update...

Finally got around to pulling the TB and adjusting the TPS. The old one would not adjust to spec, so I replaced it and adjusted as best I could with the Haynes manual. While I was there I cleaned up the TB and intake.

Idles very nice now and the roughness at 1000-1200 rpm is gone. Does anyone have a really idiot proof guide on how to adjust the TPS? I have a bit of hesitation when I first start out, but is gone almost immediately - like a cold start hesitation with carbs. I'd like to verify my adjustment with something other than the Haynes book.

Thanks.

-Aaron

 

[AKFJ62]

try changing the fuel filter. mine was doing the same thing and I changed the cap, wires, rotor, coil,and the fuel filter it fixed my problem.

 

[gnomesliv]

My carb being adjusted helped out my idle issues tremendously.

 

[yeahmag]

I should clarify that the hesitation only occurs when the truck is first started and pulls away. Other than that it's perfect. I still feel that it's a poorly adjusted TPS as that's the only thing I've changed.

-Aaron

 

[RockDoc]

Here you go:

 

[yeahmag]

Thanks.