Low idle to no idle (1 Viewer)

[Zjohnsonua]

I hope this doesn't end up as another dead end low idle speed thread, so here's to hoping the 1FZ gurus are feeling chatty.

I'm working on a '94 FZJ80 (~260k miles) which my dad bought last weekend. It made the 9 hour drive home like a champ; albeit it had a low idle speed throughout the trip. Now it won't idle unless a touch of throttle is applied at start, but will drive normally otherwise.

Work done thus far:

-VAFM checks out to FSM.
-Unplugging O2s before starting doesn't cause any change.
-Unplugging the IAC before engine start causes the predicted wide RPM swings after starting.
-Unplugging IAC after engine start causes no change.
-IAC ohms out to FSM in all circuits.
-TPS ohms out to FSM.
-Spot spraying ether over the vacuum lines, around the valve cover seals and bolts, and around the brake booster didn't excite anything.
-Hose from VAFM to TB was replaced by PO (still sprayed ether at joints, no change)

I'm hoping the DMM can be used for a few more things before swapnostics gets involved.

Any hints? Thanks in advance, everyone.

 

[Rifleman]

I just went through a problem with a ruff idle just a few days ago. I'm not sure if what i did to fix my problem will help you at all, but it might still be worth a read so I'll provide a link to the thread.
No check engine light, ruff idle problem
One last thing i'd like to recommend, make sure you check each and every pin for corrosion on every connector you take apart. Even though most of the connectors used on our trucks are supposed to be weather/water tight, they can still get wet inside. Thereby leading to corrosion, causing all kinds of weird electrical problems.

 

[toastyjosh]

Mine had a crack in the intake tube, it was causing really low idle.

 

[Desert Dino]

i had low idle until i removed the VSV canister PAIR and EGR and now i have solid idle 650 RPM ( measure by toyocom OBD1 its 94)

 

[ppc]

If you disconnected the battery the ECM will need to relearn settings. I would drive it on a few short trips before dismantling everything otherwise you may cause more issues that will be hard to diagnosed if there are multiple problems.

 

[cruiserdan]

^This^

ANY time ECU power is interrupted on a 93-94 the curb idle needs to be re-learned. The process requires a series of engine start cycles. Here is what I do:

Start the engine and allow it to warm up until the idle drops. Shut it off and leave it off for at least 20 seconds. Re-start and let it run long enough for the idle to stabilize. Shut it off and wait again. Do this several times and you should find the idle to come up a little each time.

Footnote: Do carefully examine the air intake hose for cracks as well.

 

[Zjohnsonua]

Little update. The truck needed a valve cover gasket replacement, so I did that today. As part of it I gave the throttle body and IAC a cleaning. It was surging at first, but the battery had been disconnected. Once it warmed up, it was purring at 800. It hasn't done that to date.

Thanks for the ecm learning info. I'll give the ecm the chance to do it's thing and then report back.

The hose has been replaced with a silicone type. Nice product.

Edit: I also resealed the IAC. The o-ring had long ago hardened.

 

[inkpot]

If the valve cover gasket was leaking air it would be a problem.

 

[Zjohnsonua]

Just a little section was missing . Couldn't believe they installed it like that. And to top it off, they put a big gob of RTV in to fill the gap.

 

[Qball]

Nice, there is your vacuum leak for sure

 

[Zjohnsonua]

4 cold starts (20-40F around here lately), several of the learning cycles CDan described, and a few errand trips later, the idle seems to have found its new home just shy of 800 in Park. Little less in gear. I'll call it a day on this one.

Thanks guys.