IAC problem......I think

  #21  
Old 12-05-2016, 08:38 PM
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Originally Posted by pierce View Post
note, btw, the IAC is normally not switched full on/open, rather the ground signal to it is pulsed by the ECU with a duty cycle. more ground time == more air, less ground time == less air. 50% pulses would result in it being about half open.
Great! Thanks for all your help, again. Next time it acts up I should be able to track down the source.
 
  #22  
Old 12-07-2016, 06:43 PM
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Originally Posted by pierce View Post
note, btw, the IAC is normally not switched full on/open, rather the ground signal to it is pulsed by the ECU with a duty cycle. more ground time == more air, less ground time == less air. 50% pulses would result in it being about half open.
One final follow up question, if I may. My car runs well now, most of the time, but once in a while dips but quickly recovers. Even though my IAC valve was cleaned and it opens and closes perfectly off the battery, is it possible for the springs inside to weaken with age and that combined with the pulsating signal cause a slow response?
 
  #23  
Old 12-07-2016, 06:56 PM
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i would think weaker springs would cause it to open more rather than not enough, but since the idle circuit is a sort of servo feedback thing, the ECU should self-compensate

cracked hoses on on the idle air valve are definitely sources of excess air which can cause all sorts of running issues.
 
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Old 12-07-2016, 07:51 PM
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Originally Posted by pierce View Post
i would think weaker springs would cause it to open more rather than not enough, but since the idle circuit is a sort of servo feedback thing, the ECU should self-compensate

cracked hoses on on the idle air valve are definitely sources of excess air which can cause all sorts of running issues.
Good follow up, thanks.
 
  #25  
Old 12-11-2016, 05:16 PM
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Originally Posted by pierce View Post
i would think weaker springs would cause it to open more rather than not enough, but since the idle circuit is a sort of servo feedback thing, the ECU should self-compensate

cracked hoses on on the idle air valve are definitely sources of excess air which can cause all sorts of running issues.
At this point, I guess you could call this "beating a dead horse". But what the hey. Thinking back to when my engine last dipped and died, I remember that I could not restart it immediately. It would just crank and crank. But if I let it sit about 2 or 3 minutes it would start but any throttle and it would die again. I even tried to start it slightly off idle so the TPS would click and the IAC would be inactive. Finally, after about 5 minutes it would start and run like nothing happened. Obviously, something electrical had to re-set. I may have more than the IAC involved in this. Do Bosch systems have to reset after a fault? And I don't know if this is related but my voltage regulator went out over the weekend. Won't charge(dash lights on), yet alternator(Denso) itself is fine. Before it went out, with engine running I got 13.6 volts. Even if the alternator was intermittently crapping out, right after it died there was enough battery voltage to start the car. BTW, I was at an intersection with cars behind me so I didn't have the time or tools to check the ECU. Any ideas?
 
  #26  
Old 12-11-2016, 07:39 PM
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the LH2.4 ECU has very limited adaptation memory. disconnecting the battery for a few minutes will totally reset it, but so will 5 minutes of driving. LH2.2 doesn't have any adaptation at all.
 
  #27  
Old 12-11-2016, 10:44 PM
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Originally Posted by pierce View Post
the LH2.4 ECU has very limited adaptation memory. disconnecting the battery for a few minutes will totally reset it, but so will 5 minutes of driving. LH2.2 doesn't have any adaptation at all.
So how would that apply? Or would it? What exactly do you mean by "adaption memory"?
 
  #28  
Old 12-11-2016, 11:58 PM
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the LH 2.4 ECU remembers the optimal injection ratio trim based on monitoring the O2 sensor and MAF input air values and RPM. but even if this memory is forgotten, it comes up with a default map thats good enough, then refines it as you go through various driving conditions, and in just a few miles wil have relearned.
 
  #29  
Old 12-12-2016, 09:43 AM
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Originally Posted by pierce View Post
the LH 2.4 ECU remembers the optimal injection ratio trim based on monitoring the O2 sensor and MAF input air values and RPM. but even if this memory is forgotten, it comes up with a default map thats good enough, then refines it as you go through various driving conditions, and in just a few miles wil have relearned.
Ok, I understand the concept, but how would this apply to my situation? I had to wait for it to restart and then I couldn't give it any throttle or it would die again. If it returned to the default map I should have been able to give it throttle and drive away.
 
  #30  
Old 01-21-2019, 09:00 AM
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Thanks for that update. My 90 Regina car is doing the same thing and I was a Volvo tech for 30 years....go figure. I repaired that line several years ago, but it's time to look again. Now it's Jan. 2019 and the car is almost 30 years old. I also have learned that all of those multiplug connectors that use soft, rubber insulators eventually fail because the rubber insulators disintegrate and the barrel contacts back out. Goes for the suppression relay and the ECT plug, which I fixed last night.
--Paul Smith, Raleigh, N.C.
 
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