Idle Issues - Exhaustive and Comprehensive!
12-18-2009, 09:11 AM
#1
Idle Issues - Exhaustive and Comprehensive!
The purpose of this thread is to become or aid in planning out an idle problem diagnosis sticky. The focus is on 22re and 3.0 engines since that covers the vast majority of engines in this subforum.
Hopefully we can compile a body of organized information that will allow users a one-stop-shop for idle troubleshooting. Ideally the flow of information would allow a user to match up his or her idle symptoms to a comprehensive list of idle symptoms, e.g., surging, stumbling, too high, too low. These symptoms will be connected to possible causes, e.g., sticking throttle, bad AAV, etc., through some sort of logical decision making process (when does the symptom happen, how bad is it, and so on). Then the user can determine which troubleshooting route to pursue first and have quick access to that information. We could implant some DIY info right into the stick and include links, such as to 4Crawler's TPS adjustment site.
Some of the members who are well versed in Toyota-ese may also want to include some discussion of how the idle circuit operates to provide users with the theory necessary to uncover unique problems.
Let's get some thoughts rolling and figure out the most user-friendly way to do this.
Hopefully we can compile a body of organized information that will allow users a one-stop-shop for idle troubleshooting. Ideally the flow of information would allow a user to match up his or her idle symptoms to a comprehensive list of idle symptoms, e.g., surging, stumbling, too high, too low. These symptoms will be connected to possible causes, e.g., sticking throttle, bad AAV, etc., through some sort of logical decision making process (when does the symptom happen, how bad is it, and so on). Then the user can determine which troubleshooting route to pursue first and have quick access to that information. We could implant some DIY info right into the stick and include links, such as to 4Crawler's TPS adjustment site.
Some of the members who are well versed in Toyota-ese may also want to include some discussion of how the idle circuit operates to provide users with the theory necessary to uncover unique problems.
Let's get some thoughts rolling and figure out the most user-friendly way to do this.
12-18-2009, 09:32 AM
#2
First and foremost in my humble opinion when dealing with an idle issue start with the cheap easy stuff. It's always best to locate the problem first instead of throwing parts at it. I,ve obviously learned this the hard way a few times.
1. check the obvious stuff. I.E. is the engine getting fuel, spark, and, air? Diagnosing these first can send you in a general direction.
2. what things have you done to the vehicle recently that could have affected the running capability? I.E. mud bog, weather changed, bad gas, or something as simple as fuel additives.
3. Is this a chronic problem (getting worse as time goes by)?
4. When does the symptom occur? I.E. throughout the rpm range, or when the engine is cold, or hot for that matter?
For me when dealing with any idle issue i first check the plugs, then the coolant, vaccum leaks, fuel pressure, and intake system including the throttle body. Keep in mind nine times out of ten it's the simple stuff that goes first and when checked can save you headaches in the future. 4crawler's site has been key in keeping my truck running and i will frequently go back to it just to educate myself for the future. Many of us on yotatech owe him a big thankyou!
1. check the obvious stuff. I.E. is the engine getting fuel, spark, and, air? Diagnosing these first can send you in a general direction.
2. what things have you done to the vehicle recently that could have affected the running capability? I.E. mud bog, weather changed, bad gas, or something as simple as fuel additives.
3. Is this a chronic problem (getting worse as time goes by)?
4. When does the symptom occur? I.E. throughout the rpm range, or when the engine is cold, or hot for that matter?
For me when dealing with any idle issue i first check the plugs, then the coolant, vaccum leaks, fuel pressure, and intake system including the throttle body. Keep in mind nine times out of ten it's the simple stuff that goes first and when checked can save you headaches in the future. 4crawler's site has been key in keeping my truck running and i will frequently go back to it just to educate myself for the future. Many of us on yotatech owe him a big thankyou!
12-18-2009, 09:51 AM
#3
I'll also provide a simple example and the fix i performed for it.
Early winter last year my 22re would idle and start just fine when cold. As the truck warmed up and i started to drive it the engine would bogg and stumble throughout the rpm range. No power bad gas mileage and poor performance all around. Upon inspecton of the engine compartment i pulled the plugs to find that even though i had replaced them 2 months prior they were fouled and corroded. replaced the plugs and the truck ran fine.
For another example i recently built a new 22re for my truck and installed it this year. The previous engine had a light miss when at idle and to be honest i just got used to it. Upon replacing the motor this year the miss was still there and as always i just ignored it. Well it got a little colder and the miss was a bit more prevalent and the truck started missing and stumbling as though the plugs were fouled like last year. Well i check the plugs and they were fine. Upon inspection of my in take at the throttle body i noticed that the throttle position sensor was barely plugged in so i assumed that was the problem and plugged it in. Not so much. I proceeded to put on a new throttle position sensor and it made no change in the engines performance. I then replaced the rotor, cap, and plugs just to be safe but they didn't help. To sum it up it turned out to be the air fuel meter and i was lucky to figure that out. the only reason that i stumbled across it was i found one out of an 82 supra and swapped it in to find my idle and stumble issue was gone. Here's where 4cralwer came to my rescue on installing the TPS and testing it. http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml
Early winter last year my 22re would idle and start just fine when cold. As the truck warmed up and i started to drive it the engine would bogg and stumble throughout the rpm range. No power bad gas mileage and poor performance all around. Upon inspecton of the engine compartment i pulled the plugs to find that even though i had replaced them 2 months prior they were fouled and corroded. replaced the plugs and the truck ran fine.
For another example i recently built a new 22re for my truck and installed it this year. The previous engine had a light miss when at idle and to be honest i just got used to it. Upon replacing the motor this year the miss was still there and as always i just ignored it. Well it got a little colder and the miss was a bit more prevalent and the truck started missing and stumbling as though the plugs were fouled like last year. Well i check the plugs and they were fine. Upon inspection of my in take at the throttle body i noticed that the throttle position sensor was barely plugged in so i assumed that was the problem and plugged it in. Not so much. I proceeded to put on a new throttle position sensor and it made no change in the engines performance. I then replaced the rotor, cap, and plugs just to be safe but they didn't help. To sum it up it turned out to be the air fuel meter and i was lucky to figure that out. the only reason that i stumbled across it was i found one out of an 82 supra and swapped it in to find my idle and stumble issue was gone. Here's where 4cralwer came to my rescue on installing the TPS and testing it. http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml
12-20-2009, 09:26 PM
#4
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Ok, round two, copied and pasted from notepad.
Please note that 90% of what Im writing has been gleaned off of this board and that I have not run into most of these problems. If I get anything wrong, please let me know and I will edit to reflect. Also note that I own a 3vz and not a 22re, so my experiences are on the 3vz, and that I am pretty new to Toyotas.
Brief overview of how the idle system works (3vz and 22re)
Idle is achieved by letting a set amount of air into the engine. Modern engine controls use an electric Idle Air Control motor (IAC), but our old technology engines use a mechanical means to set idle speed, which is the air bypass (idle screw) and the Auxiliary Air Valve (AAV). The AAV is open and allows air through when the engine is cold, and when warm, closes and does not let air through. The AAV is warmed by engine coolant. Our trucks have no way to compensate on their own for vacuum leaks (which let extra air into the motor, raising the idle) or for being out of adjustment/dirty the way modern vehicles do.
Concerning a bouncing or surging idle
The reason your idle is bouncing up and down is because your idle is too high. Plain and simple. Warm or cold, your Engine Control Unit (ECU) has an idea where the idle should be (1300+- cold, 850+- warm). If you are idling too high, the ECU will try and correct the idle by cutting the fuel to the fuel injectors for a short period of time, making your idle fall. Fuel is then restored and idle raises back up. The ECU sees the idle is too high and cuts fuel, making the idle fall. Back and forth, up and down.
Most people report that their idle only bounces when they step on the brake pedal. This could be happening for two reasons, only one of which I really understand:
1. Your brake booster is basically a controlled vacuum leak. Under normal idling circumstances the engine is able to deal with the relatively small loss in vacuum when you press on your brake pedal. But with a vacuum leak large enough to create a high idle, that little bit of extra lost vacuum could throw the ECU into its fuel cut mode.
2. When you step on the brake pedal, the ECU sees this and thinks "Im about to slow down so I dont need to give as much fuel to the motor" so it cuts fuel and down goes your idle. But if this is true, why doesnt it do this when your idle is normal? Someone smarter than me please chime in.
Reasons your idle could be high
1. Idle screw out of adjustment. Screw it back in to find your idle. But beware if you have to screw it in too far (like almost bottomed out) you are just compensating for another problem like a vacuum leak, worn throttle body, intake leak, or too much fuel.
2. Coolant level low. Your AAV closes because it is warmed by engine coolant. If your coolant level is low then the AAV will never warm up enough to close, allowing too much air to enter the engine, raising your idle. The ECU knows that the engine is warm, but it sees the idle is too high. So it cuts fuel...
3. Timing too far advanced. Advancing your timing will raise your idle. I think spec for the 3vz is 10*BTDC and the 22re is 5*BTDC. Advancing your timing will gain you a little power, but the idle screw needs to be adjusted in to compensate for the bump in idle speed.
4. Too much fuel. Causes could be leaking injectors, fuel pressure too high, or adjustment of the Volume Air Flow Meter (VAFM).
5.Vacuum leaks. Vacuum leaks let in extra air and raise your idle. Our engines have a redonkulous amount of vacuum lines and any one of them could be leaking. Go along every inch of them looking for cracks, holes, splits, fraying, crusties or brittle lines. The components the lines attach to could also be leaking. An easy way to check vacuum lines is to CAREFULLY spray carb cleaner on them. If there is a hole in one the carb cleaner will be sucked in and very briefly raise the idle because you just provided the engine with a little extra fuel. This can also be done with an unlit propane torch. This method can also be used to find intake manifold and plenum leaks, although this would be pretty hard on the 3vz because most of the intake manifold is covered by the plenum.
6. AAV bad or out of adjustment. I cannot find the procedure to adjust the AAV, but you could take it apart, clean it and try again. Or replace it.
7. Throttle Position Sensor (TPS) out of adjustment. This item lets the ECU know where the throttle is (how much gas your giving it). The ECU needs to know when its closed, when its open, and how far its open.
For the record, my idle issue was due to a worn throttle blade as outlined here:
https://www.yotatech.com/forums/f116...others-196714/
Thats all for now, Im gonna get some sleep.
Please note that 90% of what Im writing has been gleaned off of this board and that I have not run into most of these problems. If I get anything wrong, please let me know and I will edit to reflect. Also note that I own a 3vz and not a 22re, so my experiences are on the 3vz, and that I am pretty new to Toyotas.
Brief overview of how the idle system works (3vz and 22re)
Idle is achieved by letting a set amount of air into the engine. Modern engine controls use an electric Idle Air Control motor (IAC), but our old technology engines use a mechanical means to set idle speed, which is the air bypass (idle screw) and the Auxiliary Air Valve (AAV). The AAV is open and allows air through when the engine is cold, and when warm, closes and does not let air through. The AAV is warmed by engine coolant. Our trucks have no way to compensate on their own for vacuum leaks (which let extra air into the motor, raising the idle) or for being out of adjustment/dirty the way modern vehicles do.
Concerning a bouncing or surging idle
The reason your idle is bouncing up and down is because your idle is too high. Plain and simple. Warm or cold, your Engine Control Unit (ECU) has an idea where the idle should be (1300+- cold, 850+- warm). If you are idling too high, the ECU will try and correct the idle by cutting the fuel to the fuel injectors for a short period of time, making your idle fall. Fuel is then restored and idle raises back up. The ECU sees the idle is too high and cuts fuel, making the idle fall. Back and forth, up and down.
Most people report that their idle only bounces when they step on the brake pedal. This could be happening for two reasons, only one of which I really understand:
1. Your brake booster is basically a controlled vacuum leak. Under normal idling circumstances the engine is able to deal with the relatively small loss in vacuum when you press on your brake pedal. But with a vacuum leak large enough to create a high idle, that little bit of extra lost vacuum could throw the ECU into its fuel cut mode.
2. When you step on the brake pedal, the ECU sees this and thinks "Im about to slow down so I dont need to give as much fuel to the motor" so it cuts fuel and down goes your idle. But if this is true, why doesnt it do this when your idle is normal? Someone smarter than me please chime in.
Reasons your idle could be high
1. Idle screw out of adjustment. Screw it back in to find your idle. But beware if you have to screw it in too far (like almost bottomed out) you are just compensating for another problem like a vacuum leak, worn throttle body, intake leak, or too much fuel.
2. Coolant level low. Your AAV closes because it is warmed by engine coolant. If your coolant level is low then the AAV will never warm up enough to close, allowing too much air to enter the engine, raising your idle. The ECU knows that the engine is warm, but it sees the idle is too high. So it cuts fuel...
3. Timing too far advanced. Advancing your timing will raise your idle. I think spec for the 3vz is 10*BTDC and the 22re is 5*BTDC. Advancing your timing will gain you a little power, but the idle screw needs to be adjusted in to compensate for the bump in idle speed.
4. Too much fuel. Causes could be leaking injectors, fuel pressure too high, or adjustment of the Volume Air Flow Meter (VAFM).
5.Vacuum leaks. Vacuum leaks let in extra air and raise your idle. Our engines have a redonkulous amount of vacuum lines and any one of them could be leaking. Go along every inch of them looking for cracks, holes, splits, fraying, crusties or brittle lines. The components the lines attach to could also be leaking. An easy way to check vacuum lines is to CAREFULLY spray carb cleaner on them. If there is a hole in one the carb cleaner will be sucked in and very briefly raise the idle because you just provided the engine with a little extra fuel. This can also be done with an unlit propane torch. This method can also be used to find intake manifold and plenum leaks, although this would be pretty hard on the 3vz because most of the intake manifold is covered by the plenum.
6. AAV bad or out of adjustment. I cannot find the procedure to adjust the AAV, but you could take it apart, clean it and try again. Or replace it.
7. Throttle Position Sensor (TPS) out of adjustment. This item lets the ECU know where the throttle is (how much gas your giving it). The ECU needs to know when its closed, when its open, and how far its open.
For the record, my idle issue was due to a worn throttle blade as outlined here:
https://www.yotatech.com/forums/f116...others-196714/
Thats all for now, Im gonna get some sleep.
Last edited by thedanned; 12-20-2009 at 09:36 PM.
12-20-2009, 09:43 PM
#5
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Thinking logically and diagnosing the problem before throwing parts & $$ at it is GREAT advice.
My idle has been unsteady for about 8 months now. It frequently drops below 500 and most recently nearly stalled. I have 113,750 original miles on my 3vze. Sometimes I feel the Runner shake when stopped at a stoplight. I replaced the air & fuel filters last summer and I have a new Magnaflow exhaust (cat & muffler) installed last month.
Today I used a half-can of seafoam in it before changing the distributor cap, rotor and NGK platinum spark plugs (not enough $$ for plug wires). After the seafoam and an hour with the ratchet, I am proud to announce my idle is rock steady at just slightly below 750 RPM.
Cap, rotor, plugs. Simple solution.
My idle has been unsteady for about 8 months now. It frequently drops below 500 and most recently nearly stalled. I have 113,750 original miles on my 3vze. Sometimes I feel the Runner shake when stopped at a stoplight. I replaced the air & fuel filters last summer and I have a new Magnaflow exhaust (cat & muffler) installed last month.
Today I used a half-can of seafoam in it before changing the distributor cap, rotor and NGK platinum spark plugs (not enough $$ for plug wires). After the seafoam and an hour with the ratchet, I am proud to announce my idle is rock steady at just slightly below 750 RPM.
Cap, rotor, plugs. Simple solution.
Last edited by GO_BLUE!; 12-20-2009 at 09:49 PM.
12-20-2009, 10:35 PM
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If you find that your idle stays high when you let off the gas, it can be your Dashpot. When the Dashpots fail they bind in certain areas and keeps your idle open, instead of letting it close all the way. Its pretty simple to check, hit the throttle and when you release the gas, if your idle stays high, check the engine bay. With your hand push the Intake butterfly thingy down. If it drops to close the throttle, and the idle drops, its likely the dashpot.
You can either replace it (but it is expensive), or you can just loosen the screw that hits the dashpot.
You can either replace it (but it is expensive), or you can just loosen the screw that hits the dashpot.
Last edited by socal_style; 12-20-2009 at 10:37 PM.
12-21-2009, 11:30 AM
#7
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I am dealing with an high idle problem with my sons 22re. Truck will idle at 1500rpm and wont kick down. Yesterday my son said it was now up to 2000rpm
Frustrating
The truck is getting a new head gasket, right now and hopefully this will uncover any issues causing the idle problem.. Loose or unconnected hoses etc
Frustrating
The truck is getting a new head gasket, right now and hopefully this will uncover any issues causing the idle problem.. Loose or unconnected hoses etc
Trending Topics
12-21-2009, 11:52 AM
#9
Metalhed, you can spray some silicone into the dashpot and that often clears it up. Also check that the filter on the end of the little hose is working. It also sounds like the throttle plate could be sticking, which is what my problem was. With the truck running, open the throttle and let it snap closed, and if you can further close the throttle plate with your hand (without excessive force) then the throttle is sticking.
12-24-2009, 04:31 PM
#13
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A little update, removed my EGR last night.. i have no more missing at idle and my idle is a dead 900.. perfect. also runs a bit better to.. REMOVE YOUR EGRs!
12-24-2009, 09:13 PM
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12-25-2009, 06:59 AM
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12-25-2009, 08:39 AM
#17
the throttle body is pretty easy to take out of the intake and the gasket is cheap. make sure you remove the TPS before you clean it. I learned that one the hard way! If you can't find a ready made gasket make your own from one of those sheats of gasket material they sell at the parts store. I usually keep a couple sheets of that stuff around the shop for emergencies. They can be purchased cheaply and come in different materials. Another cheap upgrade that can affect idle and engine performance is the PVC valve. It is often over looked and is cheap and easy to replace. When you remove the throttle body make sure and check all the little lines. Clean them and make sure there are no obstructions.
12-25-2009, 03:44 PM
#19
Maybe we should compile some more expertise before sticky-izing it.
Just as a side note, I found that silicone tape (stretches 200%, self-vulcanizing) makes an excellent sealer for air and coolant hoses that are punctured. It does often cause them to contract a little though.
Just as a side note, I found that silicone tape (stretches 200%, self-vulcanizing) makes an excellent sealer for air and coolant hoses that are punctured. It does often cause them to contract a little though.
12-27-2009, 08:44 PM
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Found this on Pirate4x4 RE why the compy cuts fuel when brakes are applied
Says Jasonmt:
"The EFI computer receives a signal from the brake circuit that tells it that the brakes are being applied. This causes the computer to shut off the injectors if the RPM's are over a certain level and the engine is in "closed loop" as engine power should not be needed if the brakes are being applied.I believe the set point for the injector cut out is 850 to 900 RPM. This is what causes the surging - your idle RPM is too high, when the brakes are applied the injectors are cut out until the RPM's drop below this level. The engine then run's again. This only happens when the engine goes into "closed loop" so this will not happen when the engine is at a higher idle speed warming up. I am willing to bet your idle speed is around 1000 RPM when this happens. To fix this problem, simply adjust your warm idle speed to 750 RPM as per the factory. "
