Low idle when HOT - next steps?

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oestlarsen

oestlarsen

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Location
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Hola,
My 120K miles 92 FJ80 is having an idle "issue." I have searched various threads, and did a lot of PM, so I listed that below.

Symptoms:
1. Truck starts great - idles w/in perfect range (smooth)
2. Truck gets a 1/4 warm - idles drops perfectly (smooth)
3. Truck get warm - idle tad lower (around 600)
4. Truck gets hot (after driving for a while) - idle drops too much - down to around 500 and has occassional complete stumble (dips down to almost zero but usually recovers) - a slight miss/roughness can be felt

Truck never hesitates when taking off and otherwise is running fantastic.

Work done:
- Thermostat
- Cap, rotor, plugs, wires (All OEM)
- Cleaned TB
- Replaced ALL 3.5MM vaccum hoses
- Checked main intake hose (could not find cracks)
- Cleaned MAF
- Cleaned IAC
- Checked TPS (was w/in spec - but I am not an Ohm meter expert)
- New EGR valve
- Valves adjusted
- Modulator lookw good/clean filter

I did have a Code 71 - EGR - which I have been chasing down but not confident gone (reset EFI a few days ago). I replaced the EGR VSV with a used one.

Next on my list is:
1. Fuel filter (I have one ready to install)

Anything I am missing? What should I attack next? Could my coolant temp sensor be sending odd messages to the ECU?

Thanks much in advance!
 
I'm kinda getting the same issue. The only thing I did prior to this is i changed the sock filter on the fuel pump. I'm gonna check all my connections to insure they are tight but i'm not real sure at the moment. It hasn't dropped to a 0 idle but it is sitting around 500 rpm when hot now.
 
Update - after my throttle body clean (was not that dirty) and after 9-12 starts/drives and having disconnected battery I no longer get CEL 71 (no codes so far) and my idle is not dipping as radically as before. I still idle a tad rough and a tad low (500) when hot. Any thoughts on what to tackle next? Running/starting/accellerating great though.
Thanks!!
 
Folks - a quick update and question:
- EGR code 71 still gone (good)
- Rough idle less, but still low and noticable (miss, and downsurge at times)
- Ran 1 can seafoam in fuel
- Can't find any vaccum leaks

Question:
In my troubleshooting I disconnected the IAC while running for kicks - (it clicks per FSM after I turn off car) - but noticed NO CHANGE to idle while running...

Is that normal and/or should it guide next troubleshooting steps?

Testing ECU coolant temp sensor otherwise next. I may check TPS again with a newer ohmmeter.

Thanks!
 
Getting a similar problem ... subscribed to see where this leads.
 
Radiator age? No clue - coolant changed recently, new thermostat and Toyota red...
 
I wanted to comment that under your "symptons", I have the exact same problem(s), BUT if I turn the truck off, then turn it back on, the idle returns no normal and gets out of that low range ... does this happen for you also ?
 
Not sure if this helps but check the large brass screw seen in front of the EFI. I think the screw is an air bypass...? I have a '92 and mine was idling as you descibed and I needed to tighten the screw for mine.
Hope this helps, Jake
 
Check the intake hose for cracks, especially in the accordion-ish part. If it's cracked, you've basically got one giant vacuum leak, but it won't affect anything until the engine warms up enough to start accepting data from all the various sensors. When it's cold, it runs in a default rich setting and the vacuum leak is canceled out by the extra fuel.
 
Thanks guys!
1. Brass screw, fiddled with it to get idle up, sounds like I could be bypassing too much. Would be nice to know where to set it.
2. Radiator, can car too hot do this? My inside temp gauge says perfect operating temp.
3. Intake hose, when I had it off I put water in it to see if any cracks. I also sprayed with tb cleaner while running.

Anybody feel like disconnecting their 3FE idle plunger while hot to see if it alters idle? As noted, no affect on mine, which leads me to two main theories:

1. Some vacuum leak I have yet to find
2. Injector off

Now, it is quest!
 
Ok - that brass screw - all the way in now. No big difference, although if any, slight improvement. With this all the way in, and IAC (idle plunger thingy) disconnected - NO impact. Seems odd...I would think the motor would not like the idle thingy disconnected and would go to X RPM.
For the helluvit - tried a higher octane gas today (87).
 
I have this exact same problem and have checked and changed everything you have plus the fuel sock, the egr wires, and the ones under the glove box, with no change. I also have a fuel filter in hand but haven't changed yet. I should get to it tomorrow afternoon or Thursday and will report. Have you tried the ECT yet? Lets get it done, it drives me nuts!



oestlarsen said:
Hola,
My 120K miles 92 FJ80 is having an idle "issue." I have searched various threads, and did a lot of PM, so I listed that below.

Symptoms:
1. Truck starts great - idles w/in perfect range (smooth)
2. Truck gets a 1/4 warm - idles drops perfectly (smooth)
3. Truck get warm - idle tad lower (around 600)
4. Truck gets hot (after driving for a while) - idle drops too much - down to around 500 and has occassional complete stumble (dips down to almost zero but usually recovers) - a slight miss/roughness can be felt

Truck never hesitates when taking off and otherwise is running fantastic.

Work done:
- Thermostat
- Cap, rotor, plugs, wires (All OEM)
- Cleaned TB
- Replaced ALL 3.5MM vaccum hoses
- Checked main intake hose (could not find cracks)
- Cleaned MAF
- Cleaned IAC
- Checked TPS (was w/in spec - but I am not an Ohm meter expert)
- New EGR valve
- Valves adjusted
- Modulator lookw good/clean filter

I did have a Code 71 - EGR - which I have been chasing down but not confident gone (reset EFI a few days ago). I replaced the EGR VSV with a used one.

Next on my list is:
1. Fuel filter (I have one ready to install)

Anything I am missing? What should I attack next? Could my coolant temp sensor be sending odd messages to the ECU?

Thanks much in advance!
Click to expand...
 
I had the same problem. I put new plugs cap rotor wires and air cleaner. Cleaned the throttle body, and iac, and still had the problem. I could find no cracks in the intake tube, however for giggles I taped the accordion part Of the intake with electrical tape, and it was fixed!! Still have not got a new intake hose.
 
Change your throttle position sensor. It only costs about $100 bucks. Since it governs your idle it seems the most likely culprit here. They don't go bad very often but when they do, it can cause the kind of problem you are describing.
 
Yeah, I also played with the 3FE "Magic Screw" today - it was not out (although I did not have a cap on it) - I played with it a tad while idling..nothing.

I also disconnected 1 plug at a time, no real change in the slight miss. At this point, the slight miss is irritating me more than the idle, which seems to be something I can live with :-)

Finally, I soaked my intake tube in WD40 - hoping it would run all around the infamous accordian cracks and something would get sucked in, nothing.

I'll go offline and stop pestering the board until I can report on a few more "real" tests...

BTW - the slight miss seems to be there even when starting car up cold - or at least comes on pretty quickly.
 
I had this happen on my 91 and it was a loose vacuum line. I had knocked it loose when doing some other work under the hood. Make sure all the hoses are connected.
 
Can I bring this thread back to life?
I have the same issue with the "miss" and idle seems to get low. Did anyone find out what the problem was?
 
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