Low idle while in gear at stop... (1 Viewer)

ColoradoBoy

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Trying to chase this down, with no luck so far. Last weekend at the end of a high country tour day, the Cruiser died on me a couple of times. Crawling, brake on.

Idle is good in P or N, but when put into gear, it drops down around 450-500 RPM.

Just recently replaced plugs, wires, cap, rotor (OEM) a few months back. FPR, FPD, and fuel pump replaced 2 years back or so. Checked vacuum hoses; found one from EGR that the steel tube was rusted and rubber hose plugged full of rust crap. Cleaned steel tube, replaced rubber hose, no change. Checked all aother vac line connections for decay/debris, all good. Removed/plugged vac hoses to EGR system, no change. Recent valve adjustment (thanks, @SUMMIT CRUISERS): is running great on the highway, but still has the idle issue at a stop while in gear. Removed/plugged vac line to brake booster, no change.

Beginning to suspect fuel injector(s) or ISC? ISC check is OK for continuity (installed), same readings as 2 years ago. EDIT: TPS? Also checks OK for continuity. I have not found any better info after hours of searching- I have a trip planned for next week and would love to have this put to bed, as it is our only working rig at the moment. Please help, and Thanks!
 
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Idle is good in P or N

What is it in park and neutral?

Checked all aother vac line connections for decay/debris, all good

When is the last time that you replaced every single rubber hose related to vacuum, including everything under the intake manifold? And verified that the passages through the intake are clear? It's pretty common for people to test the hoses through various means with positive results, yet they're still leaking. Tiny leaks across all these hoses add up.

Oh, and the obvious one: did you check the intake hose for cracks?

Beginning to suspect fuel injector(s) or ISC?

Do you mean the IAC? If so, follow the FSM and apply voltage. If you feel the IAC move, it's good. It's a stepper motor, so it just barely moves each time voltage is applied. Check how much carbon is in there when you pull the IAC.

Screenshot_20220910_110551.jpg
 

ColoradoBoy

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650 rpm in P & N

Just finished checking the vacuum hoses using compressed air. All clear. Snipped some of the ends, but could probably use new hoses, as you pointed out.
Intake hoses are new.

Does the 3FE have an IAC? I thought it was the AFM, TPS, and ISC for the air induction system. Please educate me if I'm missing something. I'll check the AFM...

Thank you!
 

ColoradoBoy

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650 rpm in P & N

Just finished checking the vacuum hoses using compressed air. All clear. Snipped some of the ends, but could probably use new hoses, as you pointed out.
Intake hoses are new.

Does the 3FE have an IAC? I thought it was the AFM, TPS, and ISC for the air induction system. Please educate me if I'm missing something. I'll check the AFM...

Thank you!
Looks like the AFM is on its way out- E1 - FC resistance bounces around a bit at open position, when it should be ZERO. All other tests come back within FSM spec. (FI-67)

Very helpful to have feedback from others to prompt & gain insight. Thank you!
 

ColoradoBoy

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Looks like the AFM is on its way out- E1 - FC resistance bounces around a bit at open position, when it should be ZERO. All other tests come back within FSM spec. (FI-67)

Very helpful to have feedback from others to prompt & gain insight. Thank you!
...or not. Looks pristine to me.
AFM  3-FE.jpg


Now what? :meh:
:bang:
 
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...or not. Looks pristine to me.


Now what? :meh:
:bang:
What electronics "look" like is irrelevant. Your eyes are not properly calibrated to read resistance. Trust your meter and FSM.

1662902096836.png


1662902152751.png
 
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I have some similar issues with my 94 Land Cruiser. I have a low idle at times and what appears to be a vacuum leak. The idle will drop/rise similar to a disconnected vacuum hose. I haven't done the starter fluid check but plan on it.
 

ColoradoBoy

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What electronics "look" like is irrelevant. Your eyes are not properly calibrated to read resistance. Trust your meter and FSM.
Thank you, Jon- a knowledgeable voice of reason, as always. Still learning to use the ohm meter and understanding electrical systems. I've always been a mechanical aptitude type of guy. The electronics aptitude for me has always been a struggle. Had to research the difference between Infinity ohms and Zero ohms, for instance... After double-checking tests this morning, I believe the AFM is good.

Going to go re-check the TPS...

Found pulsing vacuum at line "R" at idle when there should be none. Traced back to the hard pipe assy where the three VSV assys. sit next to air pump. Found a clog; trying to clear it out- hard to find anything small and flexible enough to 'snake' the line.
 
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Thank you, Jon- a knowledgeable voice of reason, as always. Still learning to use the ohm meter and understanding electrical systems. I've always been a mechanical aptitude type of guy. The electronics aptitude for me has always been a struggle. Had to research the difference between Infinity ohms and Zero ohms, for instance... After double-checking tests this morning, I believe the AFM is good.

Going to go re-check the TPS...

Found pulsing vacuum at line "R" at idle when there should be none. Traced back to the hard pipe assy where the three VSV assys. sit next to air pump. Found a clog; trying to clear it out- hard to find anything small and flexible enough to 'snake' the line.
Yea, those hard lines tend to clog up with poop from one of the diaphragms in the EGR or vacuum modulator when they start to go bad.
If the issue is ONLY at idle, then you have unmetered air entering the system. Be sure the top half of the motor is air tight. Valve cover gasket/grommets; oil fill cap; oil dipstick; side cover gasket; etc. are all good places for air leaks.
Be sure to inspect the intake plenum for hairline cracks at the bellows, or loose clamps.
 
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ColoradoBoy

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Yea, those hard lines tend to clog up with poop from one of the diaphragms in the EGR or vacuum modulator when they start to go bad.
If the issue is ONLY at idle, then you have unmetered air entering the system. Be sure the top half of the motor is air tight. Valve cover gasket/grommets; oil fill cap; oil dipstick; side cover gasket; etc. are all good places for air leaks.
Be sure to inspect the intake plenum for hairline cracks at the bellows, or loose clamps.
Thank you all- I abandoned and re-routed the vac line. Thinking more and more about removing the EGR and Air Pump system...

Double checked the TPS:

VTA-E2: .83 PASS
IDL-E2 (.03 gap): open FAIL
IDL-E2: (.04 gap): open PASS
VTA-E2 (WOT): open FAIL
VC-E2: open FAIL

New TPS being ordered...
 

ColoradoBoy

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Thank you all- I abandoned and re-routed the vac line. Thinking more and more about removing the EGR and Air Pump system...

Double checked the TPS:

VTA-E2: .83 PASS
IDL-E2 (.03 gap): open FAIL
IDL-E2: (.04 gap): open PASS
VTA-E2 (WOT): open FAIL
VC-E2: open FAIL

New TPS being ordered...
Well, maybe continue with the FSM on page FI-70 first. Out of adjustment?

EDIT: Just realized I have a '95 4R with a blown HG sitting in my driveway. Time to go scavenging... :clap:
2nd EDIT: Nope, changed the design on the '95. My '89 Pickup has a matching TPS...
 
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