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1998 Sienna will not idle-up with a/c on. Idles slow even…

Customer Question
1998 Sienna will not...

1998 Sienna will not idle-up with a/c on. Idles slow even with a/c off. Sounds like it "hunts" when idling with a/c off. Sounds like brumm, brumm, brumm instead of a smooth idle.

Mechanic's Assistant: How many miles are on the car? What size is the engine?

3.0, 240k

Mechanic's Assistant: Are you fixing your Sienna yourself? What have you tried so far?

I've removed and cleaned the idle up valve below the throttle body and the idle up valve itself with a soda blaster. The valve was initially stuck. I checked the resistance from center pin to outer ones and were ok according to the FSM from Toyota. I checked the a/c amplifier according to the manual also. Basically, I've exhausted the suggestions in the manual, but still have the problem.

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Nothing

Submitted: 7 months ago.Category: Toyota
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Answered in 3 hours by:
10/5/2017
Toyota Mechanic: eric remington,
 replied 7 months ago
eric remington
Category: Toyota
Satisfied Customers: 589
Experience: mechanic/service advisor at topline auto
Verified

if you apply light throttle pressure does idle smooth out say if you bring it up a couple hundred rpm?

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Customer reply replied 7 months ago
I think it does. The symptoms are no idle up when a/c is turned on, seems to be a little bit low even with the a/c off, it seems to "hunt" when idling meaning it idles up and down by about 75 rpm, the exhaust during this sounds like a misfire. I've removed the throttle body with the idle valve, cleaned both with a soda blaster, rinsed, dried with hair dryer. The valve now spins as freely as a motor. Did resistance check on valve from center tang (+) to both side tangs and got the proper resistance noted in RM594U. Did voltage application check to ensure valve opens and closes properly. I reinstalled with same issue - no idle up. This morning I inserted test probes into the harness end of the connector to check voltage from either side tang to the center tang on the connector. With the vehicle cold, ignition on, all accessories off, the open tang reads 12.03V and the closed tang reads 12.29. Same conditions with fan running and a/c button pushed, the open tang reads 11.95V and the closed tang reads 12.19V. It would seem to me that when the vehicle is cold, the rpm should be higher, meaning the valve should be open, so why does the close tang read a higher voltage than the open, when letting air pass should increase the rpm?
Customer reply replied 7 months ago
To answer your last question directly, if you apply light pressure to the accelerator pedal, I think it smooths out a little bit, but the "hunting" is still there. I've replaced all six plugs with NGK BKR6EKPB11 plugs recommended in RM594U. I've replaced all 3 coils, inspected the a/c amplifier with resistance readings from the manual. I've checked the fuel pressure @ 50psi. I've done resistance readings on the idle control valve and took voltage readings from the harness at the idle control valve.
Toyota Mechanic: eric remington,
 replied 7 months ago

do you have an scanner to ck fuel trims and timing?

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Toyota Mechanic: eric remington,
 replied 7 months ago

does it run fine at higher rpms cruising speed etc

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Toyota Mechanic: eric remington,
 replied 7 months ago

can you ck to see if their is a command to idle motor when ac turned on

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Customer reply replied 7 months ago
I have a scanner, but a cheap one. I checked the timing, don't know how to check fuel trims. Runs good at higher rpms. What do you mean by see if there is a command to idle motor when ac turned on?
Toyota Mechanic: eric remington,
 replied 7 months ago

When you backprobe connector at idle motor did it change or remain the same

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Toyota Mechanic: eric remington,
 replied 7 months ago

voltage

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Customer reply replied 7 months ago
Not sure what you mean by back probe. All the checks were done with the connector off the idle motor.
Customer reply replied 7 months ago
Why would the voltage be higher on the closed side when the motor is cold? Wouldn't the voltage be higher on the open side in order to allow more air to pass and increase the rpm when cold?
Customer reply replied 7 months ago
The voltages on the wire harness side of the idle motor were taken with engine cold, not running but key on. Center tang (+B) to each of the two side tangs.
Without fan and a/c button pushed, cold motor, engine not running but key on: closed = 12.29V, open 12.03V
With fan and a/c button pushed, cold motor, engine not running but key on: closed = 12.19V, open 11.95VResistance checks on the motor side of the harness check ok with ranges in the fsm.
Customer reply replied 7 months ago
Are you still there?
Customer reply replied 7 months ago
I did the test on page SF-38 in the FSM.
The engine was warmed up, pulled the air assist hose and plugged it as well as the pipe it was connected to. With the engine already running, I jumped TE1 and E1 with a wire and the idle jumped to perfect for about 3 seconds, then dropped to almost stalling and stayed there. When I remove the jumper, low idle that I had comes back. Jump the terminals again and idle comes back perfect for about 3 seconds.
Customer reply replied 7 months ago
I reconnected the hose on the air assist valve, but left the electrical connector off. I installed test leads onto the pins of the IAC valve and wired the center one (+B) to the battery positive post. I started the engine and then connected the RSC test probe to the battery negative post, closing the valve and the engine ran at about 300rpm. Then I removed the RSC probe and connected the RSO probe to the battery negative post, opening the valve, and the rpm increased. This tells me that the IAC valve is working under real conditions, although when connecting the RSC probe to the battery negative post, a strange noise is made like a vacuum leak.
Customer reply replied 7 months ago
OK I haven't heard from you since 10:16.
Can I request a different expert??????
Customer reply replied 7 months ago
With engine warmed up, disconnect IAC electrical connection.
Read voltages with engine running, in neutral, no fan, no ac, no accessories:
Center probe (+B) to RSC probe is 13.8 volts.
Center probe (+b) to RSO probe is 13.75 volts.With engine warned up, disconnect IAC electrical connection.
Read voltages with engine running, in neutral, with fan and ac running:
Center probe (+B) to RSC probe is 13.7 volts.
Center probe (+b) to RSO probe is 13.6 volts.
Is .1 volt difference enough to cause idle up????
Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago
david craig
david craig, Auto Mechanic
Category: Toyota
Satisfied Customers: 5,402
Experience: owner/mechanic at 3D Automotive
Verified

Hi Im David, thanks for visiting the site. Do the attached procedure and get back to me with the results. thanks

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Customer reply replied 7 months ago
I did the test on page SF-38 in the FSM. The attachment you sent is the same test right out of the FSM. I sent the message that I did this test on my 12:18 reply above.
Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

ok, standby while i read the results

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Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

that .1 isnt enough to cause anything. I need to look into this a bit.

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Customer reply replied 7 months ago
I took the voltages above on the harness side of the IAC connector with the engine warm and running.
Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

ok

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Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

I see nothing about cold and hot resistance readings?

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Customer reply replied 7 months ago
I took the last readings after driving and warming it up.
the very first ones I took work after it sat over night.
Both times the resistance readings were within specs
Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

ok, do you have any fault codes?

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Customer reply replied 7 months ago
Cold readings were:With fan and a/c off, engine not running,
+B to RSC = 12.29 volts
+B to RSO = 12.03 volts
With fan and a/c on, engine not running,
+B to RSC = 12.19 volts
+B to RSO = 11.95 volts
Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

ok, do you have any fault codes?

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Customer reply replied 7 months ago
I get misfire codes, but I believe those are due to the rpm being so low.
If I drive it as soon as I start it, I get no codes until I come back and let it idle.
Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

standby

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Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

what is it idling at?

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Customer reply replied 7 months ago
About 600 rpm, turn the ac on and it wants to die.
Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

ok, thanks

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Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

ok, I would like you to check the ignition timing

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Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

timing

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Customer reply replied 7 months ago
While trying to do the timing, I noticed a new problem.
I can't hold the rpm steady past about 2200 rpm. Once it hits 2200, it wants to race to 3500.I did the timing anyway and it is sitting at about 10* at idle, but the idle is not constant, as I said above, it is slow and it surges instead of smooth idle. By the way, I own two of these vans, I bought the second one because of 6 kids and we love the other one.
Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

ok, this sounds like a throttle position issue. let me look into this a bit

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Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

ok, This TSB needs complied with

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Customer reply replied 7 months ago
As noted above, I've already replaced all three ignition coils. Also, I only get the misfire codes when idling, I believe because it is idling much too slow. Also, how does replacing the ignition coils a second time address the "no idle-up" problem when the ac is turned on. Also, how does replacing the coils explain the .1 volt difference between the two negative sides of the idle control valve.My guess is that both sides of the valve normally see battery voltage. Depending on whether the ac is on or not, or the engine is cold or not, resistance is provided on one side or the other of the valve, rotating it to open or close the air passage, but wth the voltage virtually the same in all conditions, the valve does nothing. It seems to me that the idle control valve is not getting the proper signal (voltage) in order to function correctly.
Toyota Mechanic: david craig, Auto Mechanic replied 7 months ago

Ill open this up to the others. you are too concerned with the IAC and its not the issue. Good luck

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Customer reply replied 7 months ago
The TSB you attached addresses the misfires, and says to switch coils and replace them, but I've already replaced all three coils. Will replacing the coils or swapping them around fix the low idle condition or the no idle up when ac is turned on??
Customer reply replied 7 months ago
What does opening this up to the others mean? Is there a team of experts?
Customer reply replied 7 months ago
Can I have a different expert????
Customer reply replied 7 months ago
David - are you still with me???
Toyota Mechanic: Peter Bagley, Auto Service Technician replied 7 months ago
Peter Bagley
Peter Bagley, Auto Service Technician
Category: Toyota
Satisfied Customers: 1,199
Experience: master tech at Toyota dealer
Verified

Hello , another tech here , do you still require help?

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Customer reply replied 7 months ago
I am still working on the problem.
Have you read through the string so that you know what has been done so far?
The voltages that I read off the harness end of the IAC are what concern me. The last tech said that IAC was not the problem, and he is right, but the signal voltages being sent to the IAC are within .1 volts of each other which is not enough potential difference to move the valve. I don't know why David Craig lost his cool, I was only stating facts and asking logical questions to try to get to a solution.
Customer reply replied 7 months ago
As mentioned above, I have two of these vans, both 1998 one LE (with the problem) and one XLE (that runs perfect). My next plan of attack is to take voltage readings on the harness end of the good van and compare them to the no good van. I believe that the IAC is not getting good signal voltage from the ECM. This also could be caused by one or both of the temperature sensors on the pipe near the thermostat. I'll check those if I get a greater potential difference on the voltage checks on the good van from the harness end of the IAC valve connector.
Customer reply replied 7 months ago
OK, side by side comparison:Voltages taken with both vans sitting over night and not started in the morning, outdoor temperature 66*F.
IAC electrical connector removed, key on, all accessories off.
Voltages taken from the harness end of the IAC electrical connector.
Good van (1998 Sienna XLE):
+B to RSO = .35 volts
+B to RSC = 12.4 volts
Bad Van (1998 Sienna LE):
+B to RSO = 12.1 volts
+B to RSC = 12.4 volts
The good van has a potential difference of 12 volts while the bad van has a potential difference of .3 volts.
Doesn't this mean that the bad van's potential difference is not enough to move the valve far enough to make a difference in the cold idling rpm? The good van runs at about 1400 rpm when first started from cold. The bad van runs at about 600 rpm all the time hot or cold unless you turn on the ac which labors the engine down to about 500-550 rpm. Can this also explain why there is no idle up when the ac is turned on?So what can cause the bad van's voltage readings to be virtually identical between +B-RSO and +B-RSC?
Customer reply replied 7 months ago
If the two voltage readings on the bad van are within .3 volts of each other, does this mean that for some reason the ECM thinks that the engine is at its normal running temperature? Once the van is at its normal running temperature, I assume that when the AC is turned on, resistance is applied to one side of the valve or the other, which allows the opposite side to overcome it, so the valve rotates slightly to increase engine rpm. As I mentioned above, if the ECM thinks that the engine is already at normal operating temperature when you first start it, will the valve move at all? Can the temperature sensors on the thermostat pipe cause bad readings to the ECM and cause the low rpm that I'm seeing?
Customer reply replied 7 months ago
I guess the next steps will be to remove and test the two temperature sensors on the pipe where the thermostat is using the procedure in the FSM.
Customer reply replied 7 months ago
is anybody there????
Customer reply replied 7 months ago
I did the testing on the ECT (Engine Coolant Temperature) sensor on page SF-57 of the FSM.The Sienna LE (no good one)
2.0k ohms @70*F
.10k ohms @212*FThe Sienna XLE (good one)
1.6k ohms @ 70*F
.10k ohms @ 212*FSo what do I do now?
Customer reply replied 7 months ago
I still need help here...or my money back.
Customer reply replied 7 months ago
OK, I want my money back
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