Trying to fix poor idle
12-17-2008, 09:20 AM
#21
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The only way I know to test a knock sensor is hooking up a scope(graphing meter will work)..then tapping the side of the block with a hammer to recreate a "ping"..but you need a really fast meter to see this....Because knock sensors are "piezio sensors" menaing they need to see a "concusion" to generate low level voltage..ie a "ping"..then that voltage is sent to the computer and as long as that voltage is present the ECM retards timimg...But as soon as there is no voltage the ECM puts timing back to where it was....It cannot keep the timing retarded for very long or else vehical will overheat,cat can be melted down.........Good luck testing one..its hard as hell even for a professional tech at the dealer.......
About the fully closed throttle,its talking about the angle the TPS is seeing,you can see this with a scan tool..Basically if the throttle plate angle from the TPS is under 10 degrees that ECM opens the IAC all the way,The ECM will partially open the IAC if the angle is over 10 degrees,but generally not much depending on rpm,ect...and fully closed at WOT,which for the ECU is about roughly 70 degrees of TPS throttle angle.
That being said if your TPS is reading 5-7 degrees idle might be a little low,but generally fully opening of the IAC can get idle smooth,now 1-2 might be a problem..On the otherhand if the TPS is reading over 11+ degrees at idle the ECM might not be opening the IAC valve all the way ..causing low idle condition..
The real question is have you removed the IAC and cleaned it on the bench? and used a small screwdriver to work the sliding valve back and forth cleaning it?......If not this point is moot,it is the only way the ECM can control idle speed..
The IAC has a very weak motor with a return spring..any small piece of carbon/varnish will cause it to stick w/o codes...causing low idle
About the fully closed throttle,its talking about the angle the TPS is seeing,you can see this with a scan tool..Basically if the throttle plate angle from the TPS is under 10 degrees that ECM opens the IAC all the way,The ECM will partially open the IAC if the angle is over 10 degrees,but generally not much depending on rpm,ect...and fully closed at WOT,which for the ECU is about roughly 70 degrees of TPS throttle angle.
That being said if your TPS is reading 5-7 degrees idle might be a little low,but generally fully opening of the IAC can get idle smooth,now 1-2 might be a problem..On the otherhand if the TPS is reading over 11+ degrees at idle the ECM might not be opening the IAC valve all the way ..causing low idle condition..
The real question is have you removed the IAC and cleaned it on the bench? and used a small screwdriver to work the sliding valve back and forth cleaning it?......If not this point is moot,it is the only way the ECM can control idle speed..
The IAC has a very weak motor with a return spring..any small piece of carbon/varnish will cause it to stick w/o codes...causing low idle
Okay, I get it, I won't be testing the knock sensors myself!I have been thinking that the TPS sensor might be the problem but the resistance seemed to check out. I will test it one more time against the specs in the FSM using the technique on 4Crawler's site. I would much rather find out that the TPS is bad and causing the IAC not to open enough rather than a bad IAC. The IAC is an expensive part compared to the TPS!
And once again, I have bench cleaned the IAC using throttle body cleaner, a paper towel and a qtip. It does not seem to be sticking at all when I hook it up to the battery... But, I did not use a screwdriver in the manner you suggested, so maybe I will take it apart one more time and clean it just for good measure.
Oh, and I am guessing that a handheld computer hooked up to the OBD port could tell me what the ECM is registering as far as throttle angle. Is that correct?
Last edited by mjwalfredo; 12-17-2008 at 09:21 AM.
12-17-2008, 09:30 AM
#22
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The reason why i mention the knock sensor is because of the "wire problem". If you purchase the scan box from URD and use your laptop it is really easy to capture the knock sensor signal....even for a novice
Have seen knock sensors do odd things.....I just like eliminating all posibilities and it is relatively easy to do.
In your previous post you said you checked out the TPS and various sensors so i thought you had ruled out this variable along with the throttle body settings.
Has the throttle body settings ever been messed with?
I started to have this same problem on my 97 4unner, 4wd, 5Spd.....but was crashed into and the truck was totaled.
When mine did it, i would just touch the throttle some and it would go back to normal. And it only happend when the AC was on.....
I agree LTD though that it is that IAC not getting the right signal or it is wore out or?? Maybe it is not getting the Idle up signal at all.
The computer should be looking at the RPMs and seeing that it has dropped below where it should be and idle up--right? THe wires going to the IAC valve are good because you tested those..Does your FSM have a section describing all the sensors affecting idle?
Check throttle body bushings--maybe cap all vacuum ports going to the intake so you can isolate the IAC valve.
Sorry this was long post--just htrowing stuff and ideas out there
Have seen knock sensors do odd things.....I just like eliminating all posibilities and it is relatively easy to do.
In your previous post you said you checked out the TPS and various sensors so i thought you had ruled out this variable along with the throttle body settings.
Has the throttle body settings ever been messed with?
I started to have this same problem on my 97 4unner, 4wd, 5Spd.....but was crashed into and the truck was totaled.
When mine did it, i would just touch the throttle some and it would go back to normal. And it only happend when the AC was on.....
I agree LTD though that it is that IAC not getting the right signal or it is wore out or?? Maybe it is not getting the Idle up signal at all.
The computer should be looking at the RPMs and seeing that it has dropped below where it should be and idle up--right? THe wires going to the IAC valve are good because you tested those..Does your FSM have a section describing all the sensors affecting idle?
Check throttle body bushings--maybe cap all vacuum ports going to the intake so you can isolate the IAC valve.
Sorry this was long post--just htrowing stuff and ideas out there
Last edited by hross14; 12-17-2008 at 09:37 AM.
12-17-2008, 09:46 AM
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Well, I am a novice for sure but I did test the TPS, IAC and MAF. We can most likely rule that stuff out but I am going to test once more just in case I made a mistake.
As far as I know, the throttle body settings have never been messed with. The paint marks on the throttle stop screw looked like factory.
And, it doesn't matter if the A/C or defroster is on or not. It is like this once the engine gets to full operating temp for a little while.
I don't think this has anything to do with the problem but I will mention it just in case:
The only serious problem I have ever had with this motor is about 5 years ago, the water pump started leaking and I didn't have a clue until the motor started pinging and the temp shot way up. I drove it like this a couple times before I brought it in.
Then all hell broke loose because the dealership didn't tighten the crank bolt all the way when they did the timing belt at the same time as the water pump. I drove all the way from New Orleans to Columbia, SC with a loose bolt. I knew because the belts kept coming off and luckily I had the right size socket to hand tighten it enough to drive about 100 mi or so before it would happen again.
I had the master tech at the dealership in Columbia put everything back together with new parts including a new crank shaft pulley and they said it checked out fine. It does have some slight scaring on the end of the crank from the loose bolt though.
It seemed to run fine after the whole ordeal, but maybe it could be connected with my problems I am experiencing today.
As far as I know, the throttle body settings have never been messed with. The paint marks on the throttle stop screw looked like factory.
And, it doesn't matter if the A/C or defroster is on or not. It is like this once the engine gets to full operating temp for a little while.
I don't think this has anything to do with the problem but I will mention it just in case:
The only serious problem I have ever had with this motor is about 5 years ago, the water pump started leaking and I didn't have a clue until the motor started pinging and the temp shot way up. I drove it like this a couple times before I brought it in.
Then all hell broke loose because the dealership didn't tighten the crank bolt all the way when they did the timing belt at the same time as the water pump. I drove all the way from New Orleans to Columbia, SC with a loose bolt. I knew because the belts kept coming off and luckily I had the right size socket to hand tighten it enough to drive about 100 mi or so before it would happen again.
I had the master tech at the dealership in Columbia put everything back together with new parts including a new crank shaft pulley and they said it checked out fine. It does have some slight scaring on the end of the crank from the loose bolt though.
It seemed to run fine after the whole ordeal, but maybe it could be connected with my problems I am experiencing today.
Last edited by mjwalfredo; 12-17-2008 at 09:57 AM.
12-17-2008, 10:41 AM
#25
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Funny--i had the same problem when i got my timing belt done (On my 1997)--but i drove it from Cali to Vegas and it died--during rush hour traffic--ON THE STRIP!!!!!
12-17-2008, 10:50 AM
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I don't know what's worse, having yours die in rush hour traffic or having my belts fall of about 5 times on the way back home making an 11 hour trip into a 17 hour trip!
12-17-2008, 05:43 PM
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It idles okay but not great when in park and neutral but when in D, 2 and L the idles drop to right above 500 rpm. It doesn't ever seem like it is going to stall but the exhaust vibrates enough to hear it in the cabin. Sometimes the shifts don't seem to be as crisp as they should either but that is mostly after coming to hard stop and then getting moving again. Finally, when I come to a stop, the truck idles normal for a few seconds but then it falls to the low idle
Exhaust vib could be due to some loose hardware and shift point have noting to do with your odd idle.
12-17-2008, 06:46 PM
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There is most definitely a problem here. I can visibly see the exhaust tube flailing back and forth when it is in gear. It smooths out nicely once I put it in neutral. Drivability is not even close to what it once was. Trust me, I have learned to deal with the quirks of a 10 yr old truck, this is not one of them.
I don't know what exactly this means but I drove it about 20 miles tonight with the IAC unplugged and it drove better than it has in months. The idle was much smoother too. I think this means the IAC is to blame but I can't be sure of that until I try my buddy's throttle body.
I think I will stop posting until I try that. Thanks for the help guys!
I don't know what exactly this means but I drove it about 20 miles tonight with the IAC unplugged and it drove better than it has in months. The idle was much smoother too. I think this means the IAC is to blame but I can't be sure of that until I try my buddy's throttle body.
I think I will stop posting until I try that. Thanks for the help guys!
Last edited by mjwalfredo; 12-18-2008 at 04:17 AM.
12-18-2008, 04:38 AM
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ehh, you could be right Redfusion. I bet unplugging the IAC is causing the ECU to do some crazy stuff so that might not be telling me anything about the IAC itself.
I am just frustrated because if this 4Runner just had an idle screw, I could easily fix it. The darn computer is keeping the idle low for some reason so I've got to really correct the problem
.
Okay, starting now, no more posts until I swap the throttle body.
I am just frustrated because if this 4Runner just had an idle screw, I could easily fix it. The darn computer is keeping the idle low for some reason so I've got to really correct the problem
.Okay, starting now, no more posts until I swap the throttle body.
12-19-2008, 05:05 AM
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Here we go again 
I swapped throttle bodies with my buddy's 98 V6 SR5 last night. He is a consulting forester and drives on a lot of dirt roads, boy was his throttle body dirty. Anyway, I didn't expect my truck to drive like it was brand new but it really, really improved the idle, throttle response, cruise control's ability to keep the speed consistently and shift timing.
So, tonight, I am going to double check my IAC, inspect the resistance on the TPS and adjust if necessary. If that fails, I think I will go ahead and order a new TPS and then only will I order a new IAC if I still don't feel satisfied with it.
Thanks for all the suggestions so far. I am confident I can fix this myself even if I have to drop 200 bones a new IAC in the end.
I swapped throttle bodies with my buddy's 98 V6 SR5 last night. He is a consulting forester and drives on a lot of dirt roads, boy was his throttle body dirty. Anyway, I didn't expect my truck to drive like it was brand new but it really, really improved the idle, throttle response, cruise control's ability to keep the speed consistently and shift timing.
So, tonight, I am going to double check my IAC, inspect the resistance on the TPS and adjust if necessary. If that fails, I think I will go ahead and order a new TPS and then only will I order a new IAC if I still don't feel satisfied with it.
Thanks for all the suggestions so far. I am confident I can fix this myself even if I have to drop 200 bones a new IAC in the end.
12-19-2008, 06:02 AM
#31
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You know--i wish i would have remembered it---but i have come accross TPS and others sensors that check out as normal when tested with a regular multi meter--but when you graph them (graphing scanner) it shows up.
But now you know--and if anything have become more familiar with your truck
But now you know--and if anything have become more familiar with your truck
12-20-2008, 01:15 PM
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It turns out the TPS was to blame for all this.
I dropped $60 total on a new TPS this morning. I could have gotten it cheaper from toyotapartsales.com but I don't care, I had to have it right away.
All the problems are gone! Thanks everyone for your help.
I dropped $60 total on a new TPS this morning. I could have gotten it cheaper from toyotapartsales.com but I don't care, I had to have it right away.
All the problems are gone! Thanks everyone for your help.
12-20-2008, 04:08 PM
#35
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Dang I wished I'd caught this like 3 days ago. I had the same exact problem on a Silverado at work and the diagnostic tree kept throwing me into a circle back to check for vacuum leaks, IAC, TPS, and back around. Finally after an hour of diagnostic and nearly throwing the scan tool at the wall I went to parts just to "test fit" a TPS. It fixed all of my concerns. I called GM TAC and told them of my problem and they needed engineers to know what they are doing to write up a correct diagnostic tree. Glad to know you fixed your concern I apologize for not chiming in earlier. I now tend to hang out at OT section.
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