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KAL
06-06-2014, 08:33 AM
Hello!
My 1.6 NA has problems with high idle when coming to a stop, such as at a red light.
When hanging, idle speed is around 1800-2000 rpm. Somethimes (not always) it idles high it then drops to 800 after 5-10 seconds, other times it just stays at 1800-2000.

Mostly it's idling perfect. The car runs fine at idle, hot and cold. Response is spot on, it doens't hesitate, it's not fluctuating.
Is the attenuation of gas-wire that does not work? Or, does this sounds like a sensor problem?

RuckkehrMiata
06-06-2014, 09:44 AM
I am no pro, but you could check vacuum lines for leaks with a bit of soapy water IIRC. I think they can cause higher idles.

kung fu jesus
06-06-2014, 09:45 AM
Idle Air Control Valve. It is bolted to the bottom of the throttle body. See if the electrical connection is loose or corroded. If that checks out, you have to remove it to clean it, or replace it.

KAL
06-06-2014, 10:10 AM
Awesome, thanks — reading about IACV / ICV / ISC-failiures, your suggestion sounds correct.

KAL
06-06-2014, 07:14 PM
Short video, showing the high idle when stopped.


https://www.youtube.com/watch?v=9pgxizVr67k&feature=youtu.be

Agent☣Orange
06-06-2014, 07:49 PM
With KFJ around, who needs factory service manuals?

kung fu jesus
06-06-2014, 08:08 PM
It's like a puzzle to solve. I enjoy it. :)

Pyr0monk3y
06-06-2014, 08:30 PM
This is pretty close to my problem. This weekend I plan to quit mooching off of KFJ's wealth of knowledge and do some actual diagnosis.

drummingpariah
06-10-2014, 02:46 AM
I'm fighting the same problem with my 93, and it's become increasingly common and intense with each race event I attend. I'm happy to start a new thread, but this sounds similar enough that I believe I simply have a more advanced version of your condition.

Here's what I tried tonight:


Drove to the shop, with normal idle (~800rpm) for roughly 40% of the drive, and a ~3,000rpm idle (constant unwanted acceleration) roughly 60% of the time.
Replaced my IACV (called an ISC in the FSM, mounted to the bottom of the throttle body) with a new one. No change.
Bypassed coolant into the IACV so it loops directly to the air valve that's attached to the throttle body. No change.
Tested for vacuum leaks with soapy water, then with starter fluid (which should raise the idle if a vacuum leak exists). None found.
My experience with carburetted vehicles (lots of motorcycles, lots of Datsuns) always makes me suspicious of 'hard-to-find' vacuum leaks, so I replaced all the vac lines in the engine bay. No change.
Removed cruise control. No change.
Disconnected the throttle cable and closed the throttle plate by hand, to ensure that there wasn't any free play in the linkage. No change.
Disconnected the ISC sensor pigtail. No change.
Gave up and drove home. I may have identified a pattern on my drive where constant-speed cruising causes the high idle condition, and coming to a stop, waiting for some period of time with the high idle, then driving away temporarily relieves the high idle condition.


I suppose the next step is to check the ECU and see if I'm throwing any codes (I didn't have an FSM with me at the shop). I don't expect a pre-obd2 ECU to offer much useful information, but I'm certainly willing to give it a try. I'll give anything a try, at this point. I'm extremely frustrated.

KAL
06-10-2014, 03:38 AM
I got hold of a new throttlebody for 30 usd, with the iacv / isc / icv and the damper-spring in place, I'll change it tomorrow.
My friend told me that it could be that spring that dampens the throttle hangs and then gives in. I sprayed the spring with brake cleaner (on the old throttlebody) and would you know —*it was much better driving around yesterday. Though, could be random.

KAL
06-11-2014, 05:55 PM
Changed the complete throttlebody (with throttle-spring(?) and ICV) today — fixed it!
The old throttle-body wouldn't close properly, it would only go 95%. If i used force it closed. The old new throttlebody was much smoother.

KAL
06-11-2014, 05:55 PM
Changed the complete throttlebody (with throttle-spring(?) and ICV) today — fixed it!
The old throttle-body wouldn't close properly, it would only go 95%. If i used force, it closed.

kung fu jesus
06-11-2014, 07:18 PM
Drum,

Check the butterfly/throttlebody plate to see of if it is attached to the pivot rod or loose. May also want to run the test on the throttle position sensor (long shot, but...), the FSM ahould have the test for that.

Check the accelerator cable to see of it moves freely. It might be catching, hanging or kinked.

Since yours is a '93, is it a California car? The decals under the hood should tell you.

drummingpariah
06-11-2014, 11:59 PM
Changed the complete throttlebody (with throttle-spring(?) and ICV) today — fixed it!
The old throttle-body wouldn't close properly, it would only go 95%. If i used force, it closed.

Congratulations! Sounds like an inexpensive, relatively easy fix!


Drum,

Check the butterfly/throttlebody plate to see of if it is attached to the pivot rod or loose. May also want to run the test on the throttle position sensor (long shot, but...), the FSM ahould have the test for that.

Check the accelerator cable to see of it moves freely. It might be catching, hanging or kinked.

Since yours is a '93, is it a California car? The decals under the hood should tell you.

Not a CA car. I disconnected the throttle cable altogether, and that didn't solve the race issue. I made a blockoff gasket for the air valve (which is attached to the intake plenum, not the throttle body), and have driven 200 miles without any issues. I think I can safely say that the air valve was the problem, since I saw this problem every 5 miles of driving over the past month (around 2,000 miles).

kung fu jesus
06-12-2014, 06:30 AM
Nice isolation idea! It is just curious because the 3000 rpm idle is the unusual bit. The ECU steps in before that if the ISC fails and sticks the idle around 1800-2000.

drummingpariah
07-26-2014, 01:26 PM
Now it's on Megasquirt, but the race condition is still present. I'm going to have to collect some logs and see if I can get some sensor data that'll point me in the right direction. If not, I have an extreme solution coming up soon - info in my build thread (http://mazdaroadster.net/showthread.php?9116-Driven-Daily-NA&p=141905&viewfull=1#post141905).

drummingpariah
07-21-2015, 04:15 PM
To follow-up on this, the idle air control valve(s) had failed on the intake manifold and throttle body. I blocked them off, and the idle is now rock-solid.