Low Idle Before Big Trip, Need Advice (1 Viewer)

[Alaska ADV]

Ive avoided writing this thread for as long as I could, and did an absurd amount of searching. Cant seem to find any one person's situation that accurately replicates mine. Need some advice.

I have a 93 FZJ80 with 158k miles on the 1FZ-FE. It has been idling low for about six months now. At initial cold start, it will spike to 1,100-1,200 rpm and then immediately drop down to 600 rpm. It will stay at the 600 rpm mark for about a minute, and then drop down to 400 to 500 rpm in park or neutral. This is regardless of temperature outside. When placed into gear, it will drop down to 200 to 300 rpm and it will idle there for the rest of the drive, regardless of engine operating temperature. If I put it in reverse and make a sharp turn, it will drop even lower and feel rough.

Okay onto the things I have done, and/or checked, in hopes of solving this issue.
- Plugs and wires were replaced about 4k miles ago.
- Replaced intake tube (this actually made it idle EVEN LOWER, which almost made me pull my hair out)
- Pulled throttle body, cleaned it out thoroughly, got carbon out of every little port and passage.
- Cleaned IAC valve
- Tested IAC valve. Within FSM specs.
- Pulled TPS while running, and idle immediately started to fluctuate wildly. (Haven't been able to test TPS per FSM, but this at least indicated to me that it is doing something...)
- Checked and adjusted timing. (timing was retarded a good three degrees below stock... don't know how that happened. But I adjusted it to about three degrees advanced over stock.)
- Replaced all throttle body vacuum lines
- Replaced charcoal canister with AC Delco version (probably not relevant but Ill throw it out there just in case)
- Replaced PCV valve

I know the FSM says to check the ECT Circuit for low idle, and that was the direction that I was going to head next. I haven't been able to find much info on here about it, and I'm not a big fan of just replacing it in hopes of it working, as the sensor is pretty expensive. Does everyone think this is the next logical step to take, or should I be heading in another direction first? Should I be pulling the intake plenum and doing fuel injectors instead?

I have a big Alaska trip planned, starting at the end of May, so my hopes were to solve this before then. The necessary maintenance for pre-trip has already been allotted, and this is now starting to eat into trip funds. If I cant seem to track this issue down in time, does anyone think its significant enough to cancel my trip?

Thanks in advance for any help.

 

[ajax1]

My tps when un plugged makes truck idle up little bit does not bounce, when unplugging iac it bounces that means iac is working. Your egr could be stuck open, you can pull the main line feeding it I believe and blow or suck on that line while it is still connected to egr and see if it unsticks. Your tps might not be set correct, but if you haven't moved it from factory location setting prob ok where it at. I chantry post the fsm page of checking it if you'd like. Ect sensor for computer is the one above oil filter to the right it can affect idle also along with the afm

 

[ZackR]

I have an occasional low idle (200-400rpm) and would be interested to see what the eventual solution is. Theres no real pattern behind it, sometimes it happens when cold, sometimes when hot. It never stalls however you can tell the engine isn't happy idling at 200rpm (very rough). Most of the time the idle is near the spec of 600rpm and it hasn't been enough of an issue for me to cancel any trips.

When I tear into things to replace the valve cover gasket I plan to clean out the IAC, throttle body, test/clean the injectors, etc.. with the hopes that the idle issue gets resolved as well.

 

[Alaska ADV]

My tps when un plugged makes truck idle up little bit does not bounce, when unplugging iac it bounces that means iac is working. Your egr could be stuck open, you can pull the main line feeding it I believe and blow or suck on that line while it is still connected to egr and see if it unsticks. Your tps might not be set correct, but if you haven't moved it from factory location setting prob ok where it at. I chantry post the fsm page of checking it if you'd like. Ect sensor for computer is the one above oil filter to the right it can affect idle also along with the afm

I just went out to confirm whether I meant TPS or IAC caused the idle to fluctuate. Now when I unplug either connector for the sensors, the idle remains the same. No fluctuation with either unplugged. When I unplug the TPS, I get a CEL. Is it possible that I have a non functioning IAC, despite it having all Ohms withing spec?

 

[wchain]

I had a similar problem and I would get the AT and Brake light flicker. Mine turned out to be a loose battery cable.

 

[thedoughboy]

How old is your accelerator cable? Sounds silly but my rig had sporadic low idle. Drove fine, just idled poorly at times. Especially right after start-up. Replaced the cable and, viola, she was happy again. There are a bunch of threads on here about the cable. Be sure to go OEM as the aftermarket ones have been know to cause issues. Good luck!

 

[Alaska ADV]

How old is your accelerator cable? Sounds silly but my rig had sporadic low idle. Drove fine, just idled poorly at times. Especially right after start-up. Replaced the cable and, viola, she was happy again. There are a bunch of threads on here about the cable. Be sure to go OEM as the aftermarket ones have been know to cause issues. Good luck!

My throttle cable is new, but I dont know the age of the accelerator cable. Most likely its OEM.

 

[Alaska ADV]

In my research and inspection, I realized today that my dashpot is set up wrong. My adjustment screw is actually in backwards, so it is making no contact with the dashpot at no throttle. Im going to adjust it first thing tomorrow, but does anyone think this could contribute at all to my symptoms?

 

[harrydunn]

Following...

 

[ajax1]

I was told by seasoned Toyota mech that it your idle does not bounce when iac is unplugged it is not working correctly

 

[Alaska ADV]

I was told by seasoned Toyota mech that it your idle does not bounce when iac is unplugged it is not working correctly

I pulled while running and had no change in idle. Tomorrow I will pull and then start the vehicle. I believe that was how I got the idle to fluctuate before. Would that indicate a functioning or non functioning IAC ?

 

[ajax1]

Non should flucuate

 

[shmabs]

I'm going through similar low idle issues and came upon this thread. It may be worth reading, though you seem to have checked most of the same boxes, and to spoil the thread for you, the low idle is not fixed yet.

No More High Idle on Cold Start

When I unplugged my IAC, my idle was all over the place. I have a spare IAC (actually an entire throttle body off of a 94) that I need to test per the FSM, if it tests good and you want to try it out, you're more than welcome.

I tested two used Toyota ECT sensors, and two brand new ones from oreilly/napa and they all read exactly the same, and all just slightly below the specified resistance values, but matched the curve perfectly. I need to get my hands on a new OEM one and see how it tests.

I'm curious to see what you come up with.

 

[harrydunn]

Yep, that's my post. Sounds very similar.

 

[Alaska ADV]

I'm going through similar low idle issues and came upon this thread. It may be worth reading, though you seem to have checked most of the same boxes, and to spoil the thread for you, the low idle is not fixed yet.

No More High Idle on Cold Start

When I unplugged my IAC, my idle was all over the place. I have a spare IAC (actually an entire throttle body off of a 94) that I need to test per the FSM, if it tests good and you want to try it out, you're more than welcome.

I tested two used Toyota ECT sensors, and two brand new ones from oreilly/napa and they all read exactly the same, and all just slightly below the specified resistance values, but matched the curve perfectly. I need to get my hands on a new OEM one and see how it tests.

I'm curious to see what you come up with.

Awesome. Im going to do more testing and see where it leads. So just to be perfectly clear, so Im not running myself in circles, you pulled your IAC while running and your idle bounced around? When I unplug mine while running, it does nothing to the idle. But if I unplug it and then start the vehicle, the idle will bounce.

When you pull the ECT to test it, do you need to drain the coolant or will you not lose any?

 

[harrydunn]

You will lose a little bit.

 

[shmabs]

Awesome. Im going to do more testing and see where it leads. So just to be perfectly clear, so Im not running myself in circles, you pulled your IAC while running and your idle bounced around? When I unplug mine while running, it does nothing to the idle. But if I unplug it and then start the vehicle, the idle will bounce.

When you pull the ECT to test it, do you need to drain the coolant or will you not lose any?

I just went out and did some quick parking lot tests at work:

Truck idling at start up, unplug IAC and no change.

Truck off, unplug IAC, start truck and the idle went all over the place.

I lost minimal coolant when swapping the ECT sensor, I had the other one ready to go, so I swapped them real quick while keeping the hole plugged.

Mike

 

[Alaska ADV]

You will lose a little bit.

Okay thanks. I hadnt seen your thread before. But it definitely isnt inspiring haha. Im hoping I can solve the issue without throwing a host of parts at it. I hadnt considered the ECU voltage as a possible issue, and now Im trying to wrap my head around diving into there to test what I can.

One thing I did notice - I get no change in idle when I turn the AC on. Granted, the AC doesnt work, so that may be why.

 

[Alaska ADV]

I just went out and did some quick parking lot tests at work:

Truck idling at start up, unplug IAC and no change.

Truck off, unplug IAC, start truck and the idle went all over the place.

I lost minimal coolant when swapping the ECT sensor, I had the other one ready to go, so I swapped them real quick while keeping the hole plugged.

Mike

Thanks for the real time feed back, I appreciate it. Im heading out now to see what I can discover.

 

[Maleficio]

May be a dumb question, but have you guys cleaned your throttle body inlet yet? Carbon built up on the butterfly valve can prevent it from closing enough. I've seen this on too many vehicles. Spray some solvent on the valve and see what happens.