2000 Toyota 4Runner Engine Surging

Hi mnyota,

Thank you for the donation.

The engine is surging due to higher than expected idling speed. Excessive air is getting past the throttle plate and this would increase the idling speed. The PCM would try to regulate the spoeed by lowering it and when it lowers, the the MAP would command the PCM to increase the speed thus the surging.

Possible causes are :

1. Vacuum leakages. Check for vacuum leakages after the throttle plate.

2. IAC. Could be faulty IAC or the coolant hoses to the IAC are clogged resulting in the thermal valve within the IAC not getting the correct signal. Do you have coolant losse issues?

3. Faulty PCM.

4. Fault in air assist system.

Was any repairs done prior to this occurring?

No new repairs prior to this occuring.

I will check for vacuum leaks after the throttle plate. I am going to guess that it's the IAC. Oddly enough, I just realized last evening that my coolant was low. Not dangerously low, just lower than normal.

What coolant lines run to the IAC? I thought the IAC was an electrical sensor on the throttle body. Is this not the case?

Thanks for your response.

Dave

The IAC is attached to the throttle body and there are coolant hoses under it as the IAC is both eletrically and thermally controlled and monitored.

So, if I'm having coolant loss issues and it's related to the IAC, where is the coolant going?

Again, it's not a lot of coolant, but enough to notice.

Would you suspect my IAC is shot? Or could it be removed, cleaned, and replaced?

Do you have access to any diagrams, pictures, or videos for an R&R of and IAC on a 2000 4runner 3.4L?

I have been working on vehicles for years (mostly Jeeps) so I am able to do much of this myself. I'm just not familiar with Toyota's.

Thanks so much for your help!

When the IAC is dirty or clogged, the idling would be lower than expected. If thee is no coolant going through it, the idling speed woud be increased. I would suggest checking the coolant level and bleeding the system if necessary. If there is sufficient coolant in system, remove the air cleaner hose and unplug both the coolant hoses under the throttle body. Ensure the coolant hoses are not clogged.

The IAC seldom fails and some cleaning might help to stabilose the idling speed. If coolant is depleting, you need to test/check for leakages. It could be from hose joints or hoses themselves.

What is the best method to bleed a coolant system on this vehicle? I know that Toyota's are a little harder to bleed and if there is air in the coolant system, it can cause a host of different problems.

Also, do you have any advice on cleaning the IAC, throttle body, and MAF sensor on this vehicle? I think I'll do it all at once to make sure I get everything.

Anything else you can think of that I should check/replace/clean while I have all of this apart?

Thanks so much for your help. I do really appreciate it.

For cleaning the IAC, just do a simple job first.
Remove the air intake hose.
Get a can of carb cleaner.
At lower part of throttle body there are 2 ports. Spray carb cleaner into them and allow to soak.
Open throttle plate fully and spray some carb cleaner into it.
Use a toothbrush to clean the interior of the throttle body with throttle plate opened fully.
Start engine, might be difficult to start due to presence of excessive carb cleaner and would stumble upon starting. Run engine till it stabilises and while spraying carb cleaner into the IAC port ( lower ports ) use the throttle to balance to prevent the engine from stalling due to excessive fuel.

After a few shots of carb cleaner, the IAC should be sufficiently clean to work correctly.


To bleed the cooling system, Remove the radiator cap.If coolant is at neck of radiator, system is good.

If coolant level is low, top up and start engine with radiator cap OFF, run for 5 minutes and stop engine. Top up coolant if necessary. Do not run for more than 5 minutes as the coolant would tend to splurge out if the thermostst is not opening due to presence of air.

Restart engine and if coolant level remains constant, close radiator cap. Run to operating temperature and allow to cool before opening the radiator cap the check coolant level. Top up if ncessary. If coolant level is still very low, repeat process.

Before doing the bleeding, check the IAC coolant hoses for clogging. Disconnect one hose and apply low air pressure to it and if coolant comes out of the IAC joint, hoses are clear.

Caution : Do not perform above on a hot engine as pressurised air can cause the coolant to spray out and cause scalding.

Does it matter if the front of the vehicle is elevated or not? On ramps? Facing uphill?

I have some coolant loss, but I'm not sure where it's going. I don't see any leaks under the vehicle, I just replaced the radiator cap so I don't think it's evaporating....

I just had the oil changed and it looked great. No milky oil indicating a head gasket.

My exhaust is a little "foggy" at times when I first start it, but I'm not sure that has anything to do with it.

Any ideas? You've helped so much, how do I make another donation?

For front of vehicle to be slightly elevated slightly is ok.

If you have coolant losses and can't notice any leakages, check under the dash for signs of leakages. If any found, the heater core could be leaking.

If the reservoir is depleting as well as the radiator, then it is a leak somewhere. Most common places to leaks would be the joints. Look out for signs of oxidation as coolant would show signs of them when exposed to air.

A pressure test is the best way to get to the source of the leak.

During cold start, exhaust would emit some condensation vapor if the weather is cold so it is normal.

A bad head gasket would have the radiator depleting whereas the recovery tank would tend to overflow as th coolant is being pushed out of radiator cap due to the pressure from the cylinders leaking through the gasket.

If grey smoke is emitted after a short running time, it is oil being burnt in the cylinders and mostly due to worn valve seals.

Anytime you wish to make a donation, just click the donate link and follow the steps accordingly.

Thank you for the gesture.

All good information. I sent in another donation to this thread. Thank you.

I thought about the heater core problem. No leaking or coolant smell inside the vehicle, including the rear seat heater lines.

I've looked high and low and cannot find a source of any coolant leaks.

My brake light just came on. That wouldn't be related in some strange way, would it? Vacuum problem?

I don't know, winter is coming and I need to get this fixed before it snows!

If this were your vehicle, what would you check and in what order? I only have a limited amount of time and funds.

Thanks!

Thank you for the additional donation.

Do you mean the brake lights at rear is turning on or is it the handbrake/brake fluid level indicator?

That would depend on what I had explained earlier. If coolant is depleting both from the recovery tank and radiator, there definitely is a leak somewhere. I understand some parts store have facilities to perform pressure test on the cooling systems. Get it done to locate the source of leak. Some leaks are minimal and would not reach the ground. They would dry out unless the leak is bad.

Check all hoses joints for sings of oxidation, an indication of leaks.

This is where I would start.

Sorry, I meant the dash MIL light for the brakes.

When the ABS indicator light turns on, it means a fault in the ABS system has been detected and trouble codes are stored in the ABS control module. The ABS has been disabled under such circumstances. You would need to retrieve the trouble code to find out what is causing it. RETRIEVING DTCS NOTE: Speed sensor diagnostics and code retrieval use different DLC1 terminals with short pin connected. If a speed sensor circuit problem is suspected, see SPEED SENSOR DIAGNOSTICS . ABS Warning Light Diagnostics 1. Ensure battery is fully charged. Turn ignition on. ABS warning light should illuminate, then turn off after 3 seconds. 2. Remove short pin from DLC1. DLC1 is located in engine compartment on left side of engine. See Fig. 2 . Using a fused jumper wire, jumper DLC1 terminals Tc and E1 . If a malfunction is detected, 4 seconds will elapse and ABS warning light will begin to flash a 2-digit DTC. First number of flashes equal first digit in DTC. After a 1.5-second pause, second number of flashes equal second digit in DTC. 3. If 2 or more DTCs are stored, there will be a 2.5-second pause between each DTC. After all DTCs are flashed, there will be a 4-second pause and all DTCs will repeat. If ABS system is functioning properly, ABS warning light will flash 2 times per second. For DTC definitions, see DTC IDENTIFICATION table. For diagnostic testing procedures, see DIAGNOSTIC TESTS . 4. After replacing or repairing components, clear DTCs. If a battery cable was disconnected during repairs, all DTCs will be erased. If battery cable was not disconnected during repairs, see CLEARING DTCS .

SPEED SENSOR DIAGNOSTICS NOTE: While diagnosing speed sensors, brake system functions as a conventional system. 1. Ensure battery is fully charged. Turn ignition on. Ensure ABS warning light illuminates, then turns off after about 3 seconds. 2. Turn ignition off. DO NOT remove short pin from DLC1. Using a fused jumper wire, jumper terminals Ts and E1 of DLC1. DLC1 is located in left side of engine compartment. See Fig. 2 . Apply parking brake. Start engine. Ensure ABS warning light flashes 4 times per second. If ABS warning light does not flash, go to ABS WARNING LIGHT CIRCUIT under CIRCUIT TESTS. If ABS warning light flashes, go to next step. 3. Drive vehicle at speeds greater than 28 MPH for several seconds. Stop vehicle. Jumper terminals Tc and E1 of DLC1. See Fig. 2 . If all sensors are okay, a normal DTC is displayed (ABS warning light flashes 2 times per second). If a malfunction is detected, 4 seconds will elapse and ABS warning light will begin to flash a 2-digit DTC. First number of flashes equal first digit in DTC. After a 1.5-second pause, second number of flashes equal second digit in DTC. 4. If 2 or more DTCs are stored, there will be a 2.5-second pause between each DTC. After all DTCs are flashed, there will be a 4-second pause and all DTCs will repeat. 5. Record DTCs. Turn ignition off. Repair as necessary. See SPEED SENSOR DTC IDENTIFICATION . Remove jumper wires from DLC1. Clear DTCs. See CLEARING DTCS .

CLEARING DTCS NOTE: DTCs can also be cleared by removing ECU-B fuse (7.5-amp), located in instrument panel fuse block. However, memory for other electronic systems will be lost. 1. Remove short pin from DLC1. DLC1 is located in left side of engine compartment. See Fig. 2 . Using a fused jumper wire, jumper DLC1 terminals Tc and E1 . Turn ignition on. Depress brake pedal 8 or more times within 3 seconds. Ensure ABS warning light flashes 2 times per second. Reconnect short pin.