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NorCal Chapter Pres
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Discussion Starter #1
I've been battling with an intermittent problem on my 01 Tacoma for the past 10k miles. Most days it will work ok, some days the idle speed will be 1,000 k RPM when in Neutral (MT) and not moving, and around 2,000 rpm when in neutral and moving...

I replaced the A/F sensor and O2 sensor since I was at 153k on the stock ones anyways. I also replaced the spark plugs, wires, PCV valve and grommet, cleaned the TB and IAC and MAF and air filter during my 150k mile maint. All to no avail, it came back a couple days ago...

I even checked the TB resistance values, and IAC and they all appear normal, with no check engine light. I also checked the dashpots and all are ok. If I apply a vaccum to the rear most dashpot when the truck is idling high, the truck still idles the same.

On the Scangauge, I notice that when the truck idles normal (700 rpm +- 10 rpm), the ignition timing is at 12 degrees. The truck runs in Closed loop, and while moving and in neutral (like coasting down a hill), or even coasting down a hill in gear, or if my foot is applying a lot of throttle the truck will run in open loop.

When the truck is idling high, the truck never drops into Open loop unless I'm on the gas hard. Coasting while moving, it will run in closed loop. I also noticed that the timing is around 28 degrees when the truck is idling high.

If the truck is running normal, and I apply some throttle pressure, the timing is still around 12-13 degrees.

I disconnected my battery, and jumped the two cables and left the key in the ON position for a day in an effort to reset the ECM. It didn't matter, still was there...



I have a feeling something is causing my timing to advance too much, and is causing my truck to idle high. What would cause it?

An idea is the AC switch. If the AC switch is sending a signal to the ECM that the AC is on, how does the ECM raise the idle? Same with the power steering switch. Does the ECM use timing to raise the idle, or the IAC?

Any more advice? Truck runs fine in high idle, it's just VERY annoying.
 

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I have a high idle. Plugs and wires are new, TB cleaned, new MAF. I have a new A/F to install...

I'll check my timing on my Scangauge and let you know where I'm at.
 

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My scangauge shows a fluctuation between 8 and 12 degrees when idling regardless of temp.
 

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Steve I'd be looking for something that is making the ECU think it needs to run the idle rpm up, like a faulty temp sensor or maybe a wire or connection to it. You're on the right track with the AC and PS pump sensors but I'd look at operating temp first. Your scangauge should be seeing the temp sensor the ECU sees and give you a readout so that would be the easy way to check it for sure. If it's reading colder than it is or intermittent, you've found your culprit. It should be running somewhere around 200 degrees after it's warmed up to full operating temp. I suppose it could even be a stuck open thermostat running the engine colder than it should be.

The temp sensor that runs the gauge is not the same sensor the ECU runs from. The ECU temp sensor is the one up forward on the engine while the gauge sensor is the one at the back on top.
 

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I've been dealing with a high idle too on my 97 T100. It's a manual as well and will idle anywhere from 1000-1500, sometimes. It goes away as soon as I blip the gas, then it drops to 700. I cleaned the iac, maf, and lubed all springs on the linkages. I also checked redistance on the tps and iac, both were good.Checked for vacuum leaks also but I'm leaning towards a worn throttle body, as it has axial movement on the shaft, and it returns to normal every time I blip the gas.

My scangauge shows closed loop almost all the time, other than cold and when I'm in neutral or between shifts. My timing is always at 8-12, even at high idle around 1100. Did you check the actual timing marks on the cams and crank pulley? If its off by a tooth, that would advance it quite a bit I'd imagine. Sounds like you've been doing all the correct troubleshooting, hopefully you'll figure it out. Good luck man
 

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NorCal Chapter Pres
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Discussion Starter #7
My scangauge shows a fluctuation between 8 and 12 degrees when idling regardless of temp.
Same here. Running hot, running "cool" or running cold, it's all around 10-12. Never near 20.

Steve I'd be looking for something that is making the ECU think it needs to run the idle rpm up, like a faulty temp sensor or maybe a wire or connection to it. You're on the right track with the AC and PS pump sensors but I'd look at operating temp first. Your scangauge should be seeing the temp sensor the ECU sees and give you a readout so that would be the easy way to check it for sure. If it's reading colder than it is or intermittent, you've found your culprit. It should be running somewhere around 200 degrees after it's warmed up to full operating temp. I suppose it could even be a stuck open thermostat running the engine colder than it should be.

The temp sensor that runs the gauge is not the same sensor the ECU runs from. The ECU temp sensor is the one up forward on the engine while the gauge sensor is the one at the back on top.
I took apart the fan clutch and changed the engagement so it kicks on sooner. While wheeling the fan is slightly engaged to keep the temps cool. It had no effect because this truck was idiling high before I did the modification. Before the mod it would run 195-205. It still idled high.

The scangauge reads off the obd2 port, so whatever the ECM sees, the scangauge displays. Regardless, when the truck is warming up, the timing is normal. The Tstat only has 60k miles on it and during my 150k maint I checked it and set the jiggle valve at 6 o clock. Tstat is not the issue and the truck runs at a fairly consistent temp. It just runs on the cooler side of the spec because I modified the clutch.

I've been dealing with a high idle too on my 97 T100. It's a manual as well and will idle anywhere from 1000-1500, sometimes. It goes away as soon as I blip the gas, then it drops to 700. I cleaned the iac, maf, and lubed all springs on the linkages. I also checked redistance on the tps and iac, both were good.Checked for vacuum leaks also but I'm leaning towards a worn throttle body, as it has axial movement on the shaft, and it returns to normal every time I blip the gas.

My scangauge shows closed loop almost all the time, other than cold and when I'm in neutral or between shifts. My timing is always at 8-12, even at high idle around 1100. Did you check the actual timing marks on the cams and crank pulley? If its off by a tooth, that would advance it quite a bit I'd imagine. Sounds like you've been doing all the correct troubleshooting, hopefully you'll figure it out. Good luck man
Timing belt should be ok. If the timing belt was off, the truck would always run high or funny. I still get great gas mileage.





Testing more today, it seems that the ac would increase the timing. While idling normally, the truck without the ac on was idling 705, timing at 11 per scangauge. I turned the ac on full blast to force the compressor to run constantly. When the clutch engaged, idle went to 950, and the timing climbed till it reached 24, where it stayed.

This would make sense. If the ECM is seeing the compressor on, it would advance the timing, and because there's no load from the ac, that's probably why it idles at 1000...

I'll look into the pressure switch doing the same. If so, it's a matter of finding which one is causing the ECM to bump the timing and idle, and fixing.
 

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The ECU wants to see the operating temps up at around 190 to 200 or it's gonna run the idle speed high to warm it up.

I wasn't saying to mess with the Tstat I was saying that maybe a bad temp sensor or temp sensor circuit was telling the ECU that the engine was cold so the ECU would run a higher idle speed as it should.

If the scan gauge is saying that the temp after warm up is in the 200 degree range then good if not then you need to find out why. If you've made it so it can't get there, then undo the fucking mess that you did to make it run cold. The EFI needs those temps to run as it should and maybe you're creating your own problem. Unless you can get in there and reprogram the ECU,(not adviseable and not likely) you'll be chasing your tail in an endless circle.

Same here. Running hot, running "cool" or running cold, it's all around 10-12. Never near 20.



I took apart the fan clutch and changed the engagement so it kicks on sooner. While wheeling the fan is slightly engaged to keep the temps cool. It had no effect because this truck was idiling high before I did the modification. Before the mod it would run 195-205. It still idled high.

The scangauge reads off the obd2 port, so whatever the ECM sees, the scangauge displays. Regardless, when the truck is warming up, the timing is normal. The Tstat only has 60k miles on it and during my 150k maint I checked it and set the jiggle valve at 6 o clock. Tstat is not the issue and the truck runs at a fairly consistent temp. It just runs on the cooler side of the spec because I modified the clutch.



Timing belt should be ok. If the timing belt was off, the truck would always run high or funny. I still get great gas mileage.





Testing more today, it seems that the ac would increase the timing. While idling normally, the truck without the ac on was idling 705, timing at 11 per scangauge. I turned the ac on full blast to force the compressor to run constantly. When the clutch engaged, idle went to 950, and the timing climbed till it reached 24, where it stayed.

This would make sense. If the ECM is seeing the compressor on, it would advance the timing, and because there's no load from the ac, that's probably why it idles at 1000...

I'll look into the pressure switch doing the same. If so, it's a matter of finding which one is causing the ECM to bump the timing and idle, and fixing.
 

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NorCal Chapter Pres
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Discussion Starter #10
Dick, How is the engine running too cold, when the operating temp per the FSM is between 176-203? I would be running 200 degrees on the freeway before, empty. Loaded up for a trip, it would run hotter. Haul anything or tow, it would run more. Needle would still be in the middle, but the SG would verify higher temps...

The T-stat is also a 180 degree stat (stock).

Either way, even when warming up, the timing isn't high.
 
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