IACV failure?
05-08-04, 03:13 PM
#1
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IACV failure?
Value appears to stick open further than required resulting in the fully warmed-up steady idle speed of ~1,100 RPM. Turning on A/C will drop idle to a steady normal RPM, where it usually stays even after A/C switched off, at least until the engine speed is again rev'd by the driver. Process is very repeatable.
Vacuum, throttle plates, AWS, cold-start wax rod, MAP, E/L module, power steering switch, etc. all test fine. Only item that I can think of that's left to verify is the ECU's temperature sensor, but since the cooling fans are activated at approximately the correct temperature, I'm expecting this sensor to be reasonably correct.
I've had the IACV off and checked its resistance, cleaned with carb spray and looked at everything else. Tried pinching off any vacuum line I could reach, inlcuding the AWS line.
If I've missed anything, someone please let me know.
Vacuum, throttle plates, AWS, cold-start wax rod, MAP, E/L module, power steering switch, etc. all test fine. Only item that I can think of that's left to verify is the ECU's temperature sensor, but since the cooling fans are activated at approximately the correct temperature, I'm expecting this sensor to be reasonably correct.
I've had the IACV off and checked its resistance, cleaned with carb spray and looked at everything else. Tried pinching off any vacuum line I could reach, inlcuding the AWS line.
If I've missed anything, someone please let me know.
05-08-04, 03:19 PM
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Forgot to mention:
According to MazdaPerformance, "Your price (30% off Mazda's list price) for the IACV (N3A1-20-660) is $269.75 and for the IACV Gasket (N3A1-20-661) is $2.87.
It will take 2-3 business days for us to receive these items from Mazda USA before we could ship out an order. S+H will be $17.38 for UPS Ground Insured within the continental 48 states."
According to MazdaPerformance, "Your price (30% off Mazda's list price) for the IACV (N3A1-20-660) is $269.75 and for the IACV Gasket (N3A1-20-661) is $2.87.
It will take 2-3 business days for us to receive these items from Mazda USA before we could ship out an order. S+H will be $17.38 for UPS Ground Insured within the continental 48 states."
05-08-04, 08:48 PM
#3
A shot in the dark didn't see the TPS voltage test listed or the ISC.
Have you sprayed carb cleaner on all the vacuum lines and gasket areas? Another way to check for a vacuum leak is to cover the end of the intake elbow, it the car does not immediately stall you have a leak, although I'm not certain if this will catch a small leak. But, it did help me isolate a bad LIM gasket.
I don't have the manual in front of me is the IACV the air control valve with the 3 solenoids located on it, also 2 vacuum lines attached?
If so, I have one I could lend you I'm in St. Louis. I doubt if that is your problem. On one of my cars the resistance was a little off on one of the solenoids (ACV) so I replaced it with this spare to no avail.
You could also get one of the ACVs pretty easy since a lot of people remove theirs to simplify or to add aftermarket fuel rails.
Usually turning the a/c on ups the idle. Does the car idle lower with the rear window defroster on? Just curious how did you verify that the E/L unit was good?
Have you sprayed carb cleaner on all the vacuum lines and gasket areas? Another way to check for a vacuum leak is to cover the end of the intake elbow, it the car does not immediately stall you have a leak, although I'm not certain if this will catch a small leak. But, it did help me isolate a bad LIM gasket.
I don't have the manual in front of me is the IACV the air control valve with the 3 solenoids located on it, also 2 vacuum lines attached?
If so, I have one I could lend you I'm in St. Louis. I doubt if that is your problem. On one of my cars the resistance was a little off on one of the solenoids (ACV) so I replaced it with this spare to no avail.
You could also get one of the ACVs pretty easy since a lot of people remove theirs to simplify or to add aftermarket fuel rails.
Usually turning the a/c on ups the idle. Does the car idle lower with the rear window defroster on? Just curious how did you verify that the E/L unit was good?
05-09-04, 05:14 PM
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Books, thanks for the feedback.
As you suggested I have tested the TPS and found that both narrow and full range were right on spec. I have also replaced all the vacuum lines except for the rats-nest area itself. Seems to have increased vacuum 1-2 inches, but the idle behavior continues. I also tried spraying carb cleaner on everything in and out of sight; UIM, rats-nest, etc. Couldn't find any leaks, certainly nothing large enough to account for the idle speed. But with a fully warmed-up engine I was too afraid to spray down around the LIM area, so maybe...
The IACV is the solenoid valve mounted on the UIM next to the firewall that controls idle speed by passing air around the throttle plates. At idle conditions this is under active feedback control from the ECU. I had it off, checked its resistance to FWM spec’s and cleaned the inside with carb spray.
In my case once the engine speed actually falls to the ~750RPM range, it stays there and is very steady. For example, holding the brake and using the clutch has the same effect as the A/C, just a little harder to control. The rear defroster also affects the idle correctly, but not enough to drop the RPM down that far.
I tested the E/L unit by grounding the TEN connection at the diagnostic connector, and attached a small lamp to the FEN (I think this is right, but don't have my FWM with me right now) and B+ connector. With the ignition key on you can test each E/L input one at a time, plus neutral, clutch, etc. The lamp lights (ECU only supplies 20~30 ma so this has to be a very small lamp, or use your VOM in series) when the ECU responds to each input switch, thereby testing the entire circuit. Check out section F of FWM on Electric Load (E/L) Control System, around F-135 or so I think.
As you suggested I have tested the TPS and found that both narrow and full range were right on spec. I have also replaced all the vacuum lines except for the rats-nest area itself. Seems to have increased vacuum 1-2 inches, but the idle behavior continues. I also tried spraying carb cleaner on everything in and out of sight; UIM, rats-nest, etc. Couldn't find any leaks, certainly nothing large enough to account for the idle speed. But with a fully warmed-up engine I was too afraid to spray down around the LIM area, so maybe...
The IACV is the solenoid valve mounted on the UIM next to the firewall that controls idle speed by passing air around the throttle plates. At idle conditions this is under active feedback control from the ECU. I had it off, checked its resistance to FWM spec’s and cleaned the inside with carb spray.
In my case once the engine speed actually falls to the ~750RPM range, it stays there and is very steady. For example, holding the brake and using the clutch has the same effect as the A/C, just a little harder to control. The rear defroster also affects the idle correctly, but not enough to drop the RPM down that far.
I tested the E/L unit by grounding the TEN connection at the diagnostic connector, and attached a small lamp to the FEN (I think this is right, but don't have my FWM with me right now) and B+ connector. With the ignition key on you can test each E/L input one at a time, plus neutral, clutch, etc. The lamp lights (ECU only supplies 20~30 ma so this has to be a very small lamp, or use your VOM in series) when the ECU responds to each input switch, thereby testing the entire circuit. Check out section F of FWM on Electric Load (E/L) Control System, around F-135 or so I think.
05-09-04, 08:20 PM
#5
Nice little test for the E/L unit, I had suspected that at one time and tested what I could at with respect to ground or power at the E/L unit's connector. Eventually I just swapped it out.
The reason I was confused about the IACV is that on page F-83, that solenoid is listed as "Solenoid Valve (Idle Speed Control [ISC]".
I still suggest blocking off the intaking elbow to see if the car stalls.
It is not clear to me, but I assume you checked the IACV's resistance and it is not in spec, hence your price check with Mazda.
I may have a spare ISC, I will check.
The reason I was confused about the IACV is that on page F-83, that solenoid is listed as "Solenoid Valve (Idle Speed Control [ISC]".
I still suggest blocking off the intaking elbow to see if the car stalls.
It is not clear to me, but I assume you checked the IACV's resistance and it is not in spec, hence your price check with Mazda.
I may have a spare ISC, I will check.
05-09-04, 08:47 PM
#6
I'm am confused. I just looked at my UIM for that solenoid near the firewall. The solenoid closest to the firewall and next to the double throttle, is what I believe to be the ISC, the part number on the solenoid does not match the number you posted. I do have a spare one of these. I will try and locate the part you are indicating via its part number.
Some guys who have unstable idles and are using PFCs disconnect the ISC and it seems to help their idle. Don't know what effect this would have using the stock ecu. I would suspect that the ecu would default to some preset value. I assume you have checked for error codes.
Some guys who have unstable idles and are using PFCs disconnect the ISC and it seems to help their idle. Don't know what effect this would have using the stock ecu. I would suspect that the ecu would default to some preset value. I assume you have checked for error codes.
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