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Old 09-29-2010, 01:48 PM   #1
leftyfork
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Default IAC Motor Testing Clarification

Hi Everyone,
I have read through some very helpful posts, and one specifically from Duane from Japan ran through some good idle troubleshooting steps. I have gone through all of the usual, FIT cleaning, IAC cleaning, make sure coolant is bled, etc etc. One question I have is related to IAC and ECU behavior. When I unplug my IAC, the idle does not go down. When I plug it back in, the idle surges, but goes back to exactly the same RPMs as unplugged or plugged in. I have set the base idle higher, deliberately, to see what happens when I plug it back in, and still it stays right where it is set (higher). So, bad IAC, right? You would think that, but if I drive the car for a while the ECU appears to be able to get the idle down to 750 again. How is this happening? Is the IAC being closed over time and sticky? Is the ECU retarding the timing? I guess what I really want to know is how can I be absolutely 100% sure I need a 300 dollar IAC motor?
And also, how important is it to have the throttle position sensor to send exactly .5 volts to the ECU?

100% checked good
1. New fuel injectors
2. 31 PSI fuel pressure at idle
3. New fuel filter
4. Fuel pressure regulator checks good
5. Throttle body cleaned
6. No vacuum leaks.
7. New air filter
8. Valve lash set
9. No clogged exhaust.


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Old 10-03-2010, 10:33 AM   #2
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Default Re: IAC Motor Testing Clarification

Quote:
Originally Posted by leftyfork View Post
Hi Everyone,
I have read through some very helpful posts, and one specifically from Duane from Japan ran through some good idle troubleshooting steps. I have gone through all of the usual, FIT cleaning, IAC cleaning, make sure coolant is bled, etc etc. One question I have is related to IAC and ECU behavior. When I unplug my IAC, the idle does not go down. When I plug it back in, the idle surges, but goes back to exactly the same RPMs as unplugged or plugged in. I have set the base idle higher, deliberately, to see what happens when I plug it back in, and still it stays right where it is set (higher). So, bad IAC, right? You would think that, but if I drive the car for a while the ECU appears to be able to get the idle down to 750 again. How is this happening? Is the IAC being closed over time and sticky? Is the ECU retarding the timing? I guess what I really want to know is how can I be absolutely 100% sure I need a 300 dollar IAC motor?
And also, how important is it to have the throttle position sensor to send exactly .5 volts to the ECU?

100% checked good
1. New fuel injectors
2. 31 PSI fuel pressure at idle
3. New fuel filter
4. Fuel pressure regulator checks good
5. Throttle body cleaned
6. No vacuum leaks.
7. New air filter
8. Valve lash set
9. No clogged exhaust.


Kurt
Duane in Japan is a sharp dude and often dispenses good advice. You were not clear on what your problem is. Is it fluctuating idle or idle that is too low??
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Old 10-03-2010, 04:16 PM   #3
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Default Re: IAC Motor Testing Clarification

start checking sensors on the tb, could even be the tps acting up.
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Old 10-04-2010, 05:17 AM   #4
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Default Re: IAC Motor Testing Clarification

Sorry I wasn't clear, Rough idle. In an otherwise perfectly running engine while cruising, and at top end, the idle is very poor. Vacuum signal is solid at about 22Hg. If the AC is on, or there is an electrical load on the alternator, the idle is even worse. When in neutral or park, there does seem to be a slight skip, that could be magnified when these in gear, under load conditions occur. I installed new blue NGK wires and correct plugs. So, now I am just trying to confirm 100% testing of components. I am now starting to consider the Electronic Control Unit in the distributor, the coil (which tests OK with a meter), the timing belt tensioner perhaps, or even the timing belt itself, or maybe the air charge sensor? What is the accepted and accurate IAC motor test besides hearing it click? Is it a on off motor, where it either lets air in, or it doesn't? Because that is it's current behavior. I just don't know if it is the correct behavior.
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Old 10-04-2010, 12:12 PM   #5
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Default Re: IAC Motor Testing Clarification

Quote:
Originally Posted by leftyfork View Post
Sorry I wasn't clear, Rough idle. In an otherwise perfectly running engine while cruising, and at top end, the idle is very poor. Vacuum signal is solid at about 22Hg. If the AC is on, or there is an electrical load on the alternator, the idle is even worse. When in neutral or park, there does seem to be a slight skip, that could be magnified when these in gear, under load conditions occur. I installed new blue NGK wires and correct plugs. So, now I am just trying to confirm 100% testing of components. I am now starting to consider the Electronic Control Unit in the distributor, the coil (which tests OK with a meter), the timing belt tensioner perhaps, or even the timing belt itself, or maybe the air charge sensor? What is the accepted and accurate IAC motor test besides hearing it click? Is it a on off motor, where it either lets air in, or it doesn't? Because that is it's current behavior. I just don't know if it is the correct behavior.
Ok, a rough idle then. How do you know the idle is rough while cruising?? The IAC will only raise the idle to compensate for a load placed on the engine. It will not smooth the idle out. With the car in park, and running, try placing various loads on the engine 1 at a time and see if the idle drops and does not come back up.
1. turn your high beams on.
2. Turn your AC on.(Blower on high)
3. Turn the steering wheel from lock to lock a few times.
Do each of these and see if the idle recovers.
(The year make and model of your car would be helpful)
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Old 10-05-2010, 08:29 PM   #6
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Default Re: IAC Motor Testing Clarification

whats a timing belt?
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Old 10-06-2010, 03:39 AM   #7
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Default Re: IAC Motor Testing Clarification

The care is a 1990 Integra GS. I know I am in the wrong forum, mine is just below this one. There doesn't seem to be much idle change when turning on the AC, etc? Sometimes the idle will bump up slightly to try to maintain, but it typically drops down and the engine struggles. My main question is IAC behavior. When I have it off the intake, and apply 12 volts, the motor clicks and it allows air to pass. Removing the power, it clicks and closes, and no air can pass through. My understanding of the way an IAC valve/motor works is that it fine tunes the idle as needed. A simple open and closed functionality seems like a pretty pitiful way to compensate for idle air needs. Is this normal?
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Old 11-10-2010, 05:25 PM   #8
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Default Re: IAC Motor Testing Clarification

I am kinda haveing the same issue i have a 88 crx dx with an obd0 b18a1 swap running generaly fine but today i was driveing and all of the sudden i came to a stop and my car died just fell flat on its face died... it sounded like it was missing and i pushed it to a parking lot pulled the distributor cap and looked inside and it looked super crummy so i cleaned everything up good and put it back together and it started up so i drove it carefuly home
i get home and i check all my codes reset my ecu and the only code i now get is 14 iacv
so i mess with it for awhile and after awhile nothing it wont even start back up so im confused i took the iac off sprayed throttle body cleaner in it and let it set while i whent to eat came back a few hours later put it back on and she fired right up
although from idle if i mash gas the car dies if i baby it smoothly or tap it a few times it will idle up and rev no problem just from base idle if i quickly tap the throttle or mas it it will miss or die
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