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1998 Toyota T100 Sr5, 5 speed, 4x4, 205k, original engine, Colorado truck, no rust, sunfaded.
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Discussion Starter · #1 ·
Hey y'all, so I'm trying to fix a high idle. I've cleaned the MAF, IAC and throttle body previously. I've also shimmed my butterfly valve which helped remove some of the high idle but not all. Today I threw together a smoke machine to check for vaccum leaks. I opened the butterfly valve and pumped good ol swisher sweet into the system. I found leaks where the intake boot connects to the throttle body and a leak from the tube just to the left where the boot meets the TB and added 2 hose clamps. I retested and it seems tight now, so tight the system holds pressure with my rigged swisher smoke machine. I pulled the EFI fuse for a few mins and went on a few test drives, 30mins cool down to 30 mins cool down.

Idle when clutch is engaged after warmed up is still close to 2000 even though when I started the truck it was closer to 1500. Also when I go from 60mph, throw it in neutral and roll the rpm is 2000 and as soon as I touch the brake to slow down the rpms jump multiple times back and forth from 2000 to 1000 and ends up back on 2000. I am wondering if this is just the ECM remapping since I pulled the EFI fuse? Also if anyone has any other suggestions on my idle mystery? Or things to clean the system up since the truck has been pulling some unfiltered air for a while I assume?

My next move is try replacing the coolant temperature sensor...

I also tried fixing my electric passenger door key lock, turns out the rod that pushes and pulls on the actuator had a broken plastic clip where they connect. Wrapped some duct tape around the end and pushed it through the hole on the actuator.... Its working but hopefully it holds, next move for that is the $10 plastic clip from ebay...

Cheers!

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1995 Toyota T100 4X4
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67 Posts
Wouldn't be surprised if there were more vacuum leaks. They can be quite subtle if the hose cracks at the tip, like the PCV hose at the right of your picture, but it doesn't take much to start causing problems. I had an intermittent CEL that only went away when I pulled and inspected each hose, and replaced every one that had any cracks whatsoever.

Another tip, before you start replacing sensors, go to an auto parts store, hook a scan tool to the truck, and get a live readout from all of the sensors. If a sensor is bad, you will often see it reporting weird numbers on the scan tool. I know Oreilly will loan one out that has this capability.
 

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1998 T100 SR5 2WD
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14,860 Posts
Scan tool is yer friend. Fuel trim values at idle can tell you a lot of what's going on especially if there's a vacuum leak. The ECU will add fuel (positive fuel trim values) due to the added oxygen detection. ;)
 
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1998 T100 SR5 2WD
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A common component to leak is the brake booster. You can disconnect the vacuum hose to it and plug the hose. Look at yer fuel trims (OBDII scanner data) to see if it lowers closer to 0 or not. If it does, yer gonna need to replace the booster. ;)
 

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1998 Toyota T100 Sr5, 5 speed, 4x4, 205k, original engine, Colorado truck, no rust, sunfaded.
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23 Posts
Discussion Starter · #5 ·
Okay, sounds like I'll be visiting oriellys soon to borrow a scanner. Maybe that's why it only fluctuates between 2000 and 1000 after I touch the brakes?
 

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bluetooth scanners rule. 20 bucks and one download later, you have it all.

Im curious abt your smoker. I lost my old one and need to make a new one. Yours is a metal can you load up with charcoal and tobacco?
 

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1998 Toyota T100 Sr5, 5 speed, 4x4, 205k, original engine, Colorado truck, no rust, sunfaded.
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23 Posts
Discussion Starter · #9 ·
bluetooth scanners rule. 20 bucks and one download later, you have it all.

Im curious abt your smoker. I lost my old one and need to make a new one. Yours is a metal can you load up with charcoal and tobacco?
I just use a two way pump, it pulls air from the top hose and blows that air out the bottom. So I tape a swisher sweet into the top and it blows out the bottom. I use the can, attached to the bottom hose and clamp the can in the intake just past the MAF.
 

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1998 T100 SR5 2WD
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Yes, that's the brake booster vacuum line.

Here's a quick test. ;)
 
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1998 Toyota T100 Sr5, 5 speed, 4x4, 205k, original engine, Colorado truck, no rust, sunfaded.
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23 Posts
Discussion Starter · #12 ·
Brake booster passed all tests. When vacuum hose is removed and plugged idle is still high. So isn't the brake booster, check valve or hose according to these at home tests.

Where can I find a diagram of all the vacuum hoses so I can go through them one by one?

And is there a kit of all the vacuum hoses or would I just get similar hose and cut to size per piece?

Im still confused why the idle would fluctuate between 2k and 1200 on its own after touching the brake while rolling in neutral after highway speeds 🤔

Also what should a normal idle even be?
 

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1998 Toyota T100 Sr5, 5 speed, 4x4, 205k, original engine, Colorado truck, no rust, sunfaded.
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23 Posts
Discussion Starter · #13 ·
And I just tested my coolant temp sensor, just by unplugging it and my startup idle was 1200. As soon as I plugged it back in it went right to 2000. Have I found my culprit? Or would that occur even when unplugging a functional sensor?
 

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1998 T100 SR5 2WD
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And I just tested my coolant temp sensor, just by unplugging it and my startup idle was 1200. As soon as I plugged it back in it went right to 2000. Have I found my culprit? Or would that occur even when unplugging a functional sensor?
Was the engine at operating temp? If the coolant is cold, then the ECT is telling the ECU to increase idle speed until the engine warms up enough not to need the increased idle. Best way to test that is to see what the ECT sensor is reporting back to the ECU by using a scan tool. It should be around 186°F. ;)
 

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1998 Toyota T100 Sr5, 5 speed, 4x4, 205k, original engine, Colorado truck, no rust, sunfaded.
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23 Posts
Discussion Starter · #16 ·
Was the engine at operating temp? If the coolant is cold, then the ECT is telling the ECU to increase idle speed until the engine warms up enough not to need the increased idle. Best way to test that is to see what the ECT sensor is reporting back to the ECU by using a scan tool. It should be around 186°F. ;)
Seems like at operating temp ( highway driving for 30mins) I'm getting 68C or 155F. Which is low. So I pulled the ECT sensor and tested it and it passed a hot water test but it looked rusted and nasty when I removed it... What else would keep my coolant from reaching it's proper temperature?
 

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1998 T100 SR5 2WD
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Seems like at operating temp ( highway driving for 30mins) I'm getting 68C or 155F. Which is low. So I pulled the ECT sensor and tested it and it passed a hot water test but it looked rusted and nasty when I removed it... What else would keep my coolant from reaching it's proper temperature?
Is this an OEM thermostat or aftermarket thermostat? Have you verified that the thermostat isn't stuck open? Another possibility is that the cooling fan is on all the time. Is the fan clutch still working or has the fan been replaced with a straight drive fan with no clutch mechanism? ;)
 
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1998 Toyota T100 Sr5, 5 speed, 4x4, 205k, original engine, Colorado truck, no rust, sunfaded.
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23 Posts
Discussion Starter · #18 ·
Is this an OEM thermostat or aftermarket thermostat? Have you verified that the thermostat isn't stuck open? Another possibility is that the cooling fan is on all the time. Is the fan clutch still working or has the fan been replaced with a straight drive fan with no clutch mechanism? ;)
I am unsure if it's been replaced or OEM. I bought the truck 3000 miles ago and the owner didn't have the whole history. Would the only way to tell if the thermostat is stuck open be to drain all the coolant and visually inspect the thermostat? How would I check the fan clutch? or know of it's straight drive, like you say? Sorry, I'm not extremely mechanically knowledgeable but I am trying to learn. Thanks for your help Bam and everyone else!
 

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1998 T100 SR5 2WD
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I am unsure if it's been replaced or OEM. I bought the truck 3000 miles ago and the owner didn't have the whole history. Would the only way to tell if the thermostat is stuck open be to drain all the coolant and visually inspect the thermostat? How would I check the fan clutch? or know of it's straight drive, like you say? Sorry, I'm not extremely mechanically knowledgeable but I am trying to learn. Thanks for your help Bam and everyone else!
How long does the engine take to warm up to operating temp? I would be guessing that the thermostat is either stuck open or it's been removed. ;)

The thermostat is located off of the lower radiator hose (engine side obviously). I believe there are 3 nuts holding the lower water inlet in place. When you disconnect the lower hose, the coolant will drain out. Remove the 3 nuts and inlet housing and the thermostat should be located on the engine side. OEM thermostat and gasket part numbers are 90916-03075 and 16325-62010. When installing the thermostat, the jiggle valve will need to be in the 6 o'clock position. Toyota red coolant is about $30 at yer dealership. This will need to be mixed with distilled water to maximize the coolant life. You can use the Toyota premixed "pink" coolant if you prefer but you'll need about 2 gallons worth. ;)

When you refill the coolant, make sure you fill the engine side first by removing the upper radiator hose and fill coolant into the hose going to the engine. ;)

Snap some piccies of yer cooling fan setup and post them. ;)
 

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1998 Toyota T100 Sr5, 5 speed, 4x4, 205k, original engine, Colorado truck, no rust, sunfaded.
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23 Posts
Discussion Starter · #20 ·
How long does the engine take to warm up to operating temp? I would be guessing that the thermostat is either stuck open or it's been removed. ;)

The thermostat is located off of the lower radiator hose (engine side obviously). I believe there are 3 nuts holding the lower water inlet in place. When you disconnect the lower hose, the coolant will drain out. Remove the 3 nuts and inlet housing and the thermostat should be located on the engine side. OEM thermostat and gasket part numbers are 90916-03075 and 16325-62010. When installing the thermostat, the jiggle valve will need to be in the 6 o'clock position. Toyota red coolant is about $30 at yer dealership. This will need to be mixed with distilled water to maximize the coolant life. You can use the Toyota premixed "pink" coolant if you prefer but you'll need about 2 gallons worth. ;)

When you refill the coolant, make sure you fill the engine side first by removing the upper radiator hose and fill coolant into the hose going to the engine. ;)

Snap some piccies of yer cooling fan setup and post them. ;)
Just started a road trip to Sedona today, drove 300+ miles and coolant temp hardly reached mid
70 celcius even with some AC, averaged somewhere low 70s and high 60s. I'm keeping my fingers crossed she'll make the whole trip no problems🙏.

Why would someone remove the thermostat?

Here are some pics of the radiator and fan setup. Radiator says "Harrison GM" stamped on the top.
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Once I get back from this trip, or if I find time and the means while on the road, I'll drain it and snag a peak of the thermostat or where it should be...👍
 
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