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funkstuf
04-05-2016, 11:06 PM
I've been fiddling with an idle problem for awhile now and hoped to get it solved, but here I am. Typically idles high. When I start the car it's about 1000 rpm and when it warms up after a few minutes goes to 14-1500 rpm. I backed off the microswitch and idle screw but it stayed at high idle. I also checked the microswitch to ground and it is working properly.

I disconnected inner bulkhead on ECU and it goes to 2500. Unplugging the outer does not change anything. I tested the thermistor on the 4 pin bulkhead at the ECU and found resistance so assumed it's working. I also swapped it with another ECU I have that is known good and had the same results.

I checked around injectors and vacuum lines with carb fluid but didn't spot any leaks.
I checked the idle motor and it does hum. Also, just for good measure took it out and sprayed carb fluid in it and shook it around a bit. At one point I checked voltages on the idle motor connector and noticed 12 volts center pin, about 10 volts to one side but 0 volts to the other. I assumed that it was just not signaling one side at the time. The Lambda system does buzz.

I tested the Lambda Dwell with the engine warmed and the O2 sensor disconnected and got 44. (Using Orange wire and ground on the engine ground on the intake 4 cylinder mode)
The engine idles around 850 rpm with O2 sensor disconnected.

When I connect the O2 sensor the idle goes up to 14-1500 rpm and here's the disturbing part. The Dwell goes to about 84. I messed a bit with the air/fuel screw on the distributor and I can get the RPMs to drop to 800 but it smells like it's running to rich and wants to flood so I put it back the way it was. Also, that didn't seem to change the Dwell with the O2 sensor hooked up and I understand that it should be around 40, not 84.

In any case, the Lambda system is working very hard when the O2 sensor is hooked up.
Questions:
1.) Could a bad O2 sensor cause this because it does seem to be working.
2.) I didn't check continuity on all ECU lines, but unhooking it didn't seem to matter. I did consider that the motor might just stay in the state it was left in, and perhaps if one side's not working
3.) Any other ideas based on what I've done so far?

Bitsyncmaster
04-06-2016, 04:37 AM
If your getting vacuum advance at idle, you will be about 500 RPM to high. So I would test you have no advance by pulling the hose off the ignition distributor.

You do not use the mixture screw to set idle speed or idle smoothness. Set it with your meter and fix other problems when set correctly.

funkstuf
04-06-2016, 08:02 PM
If your getting vacuum advance at idle, you will be about 500 RPM to high. So I would test you have no advance by pulling the hose off the ignition distributor.

You do not use the mixture screw to set idle speed or idle smoothness. Set it with your meter and fix other problems when set correctly.

Thanks for the reply. With the car warmed up I can remove one or both vacuum hoses to the vacuum solenoid (one of which goes to the distributor) and it doesn't change the idle.

I did notice when I start my car from dead cold it idles at about 775 for a few minutes, then once it warms up jumps up to 14-1500 rpm. If it's already partially warmed up it will idle at 1000 for a minute or so then go to 14-1500, that part seems to depend on how warm it is.

sdg3205
04-07-2016, 12:14 AM
Dale, check your three bank enrichment screws on the butterfly assembly are in tight. I had dwell issues and these were all just loose enough to cause issues.

Bitsyncmaster
04-07-2016, 04:49 AM
Your engine takes more throttle (idle motor opens more) when the engine is cold. That is due to the oil being "thick" and other tighter tolerances.

Since your holding the 775 RPM cold that tells me your idle system is working but must be running out of it's control range as the engine heats up.

Try backing off the curb idle screw (lower screw on throttle arm) which also may need the idle switch screw to be backed off if it bottoms out on the idle switch.

If you find like I did that even with that curb idle screw backed all the way out the idle would still climb after the engine warmed up, you may have the bad deceleration springs like I had. Once I replaced the throttle assembly that fixed my high idle.

Morpheus
04-07-2016, 02:28 PM
Your engine takes more throttle (idle motor opens more) when the engine is cold. That is due to the oil being "thick" and other tighter tolerances.

Since your holding the 775 RPM cold that tells me your idle system is working but must be running out of it's control range as the engine heats up.

Try backing off the curb idle screw (lower screw on throttle arm) which also may need the idle switch screw to be backed off if it bottoms out on the idle switch.

If you find like I did that even with that curb idle screw backed all the way out the idle would still climb after the engine warmed up, you may have the bad deceleration springs like I had. Once I replaced the throttle assembly that fixed my high idle.

I had the same issue. I changed out my throttle butterflies with soft decel springs with newer, stronger ones and my idle went back to normal.

funkstuf
04-07-2016, 06:41 PM
Dale, check your three bank enrichment screws on the butterfly assembly are in tight. I had dwell issues and these were all just loose enough to cause issues.
Dave, Thanks, I did check tightness and sprayed some carb fluid around them, appears no leak.

funkstuf
04-07-2016, 07:18 PM
Try backing off the curb idle screw (lower screw on throttle arm) which also may need the idle switch screw to be backed off if it bottoms out on the idle switch.

If you find like I did that even with that curb idle screw backed all the way out the idle would still climb after the engine warmed up, you may have the bad deceleration springs like I had. Once I replaced the throttle assembly that fixed my high idle.

OK, I'll turn the throttle screws and look at the deceleration springs this weekend when I can turn a wrench. A quick test this morning before work: Unplugged the O2 sensor and started the motor and let it warm up until fans came on. The idle stayed at 775 rpm and did not waver at any time. Voltage on O2 sensor was 0.09 V when warmed up. Is it possible the O2 sensor is bad or was the idle just staying steady because the lambda system was constant at 45? (It did go to 54 when WOT pressed and idle increased a bit). Your replies help me understand more of how this thing operates and fun to try the tests.

Bitsyncmaster
04-07-2016, 07:26 PM
OK, I'll turn the throttle screws and look at the deceleration springs this weekend when I can turn a wrench. A quick test this morning before work: Unplugged the O2 sensor and started the motor and let it warm up until fans came on. The idle stayed at 775 rpm and did not waver at any time. Voltage on O2 sensor was 0.09 V when warmed up. Is it possible the O2 sensor is bad or was the idle just staying steady because the lambda system was constant at 45? (It did go to 54 when WOT pressed and idle increased a bit). Your replies help me understand more of how this thing operates and fun to try the tests.

You may have not waited long enough but that would suggest your mixture is causing the problem.

funkstuf
04-07-2016, 11:04 PM
You may have not waited long enough but that would suggest your mixture is causing the problem.

But, if I have an air leak somewhere this could still be causing it to be too lean, but the lambda system wouldn't have compensated it when the O2 was disconnected right? I'm going to check again for air leaks. I did spray carb fluid in around where the idle motor pipe goes and didn't detect anything but I never feel like that thing is sealed. I'll also carry out the idle screw tests you suggested this weekend and hopefully come up with some results to report.
Thanks for all the help here.

funkstuf
04-10-2016, 09:44 PM
Try backing off the curb idle screw (lower screw on throttle arm) which also may need the idle switch screw to be backed off if it bottoms out on the idle switch.

If you find like I did that even with that curb idle screw backed all the way out the idle would still climb after the engine warmed up, you may have the bad deceleration springs like I had. Once I replaced the throttle assembly that fixed my high idle.

I had the same issue. I changed out my throttle butterflies with soft decel springs with newer, stronger ones and my idle went back to normal.

OK Guys, thanks for the input. After checking the curb idle again it does appear the problem may be the the decel springs. Everything else seems to check out when I look very closely. After further testing it appears that the O2 sensor is working, the Lambda system is working, the idle motor seems to be working, and when the car warms up, the idle still goes up to around 1500 rpm.
Can I actually find new springs? Someone told me I have to replace the entire assembly. Morhpeus mentioned soft springs. Where do I get those? I kind of want to be ready when I pull the little W pipe off. I'm open to hear some ideas. Thanks again.

Bitsyncmaster
04-11-2016, 05:49 AM
Here is what the bad springs look like. Good springs have evenly spaced coils.

Morpheus
04-12-2016, 09:10 AM
Josh at DPI was able to sell me a set of butterflies with good springs. I'm not sure if they were reconditioned or just good used parts, but they worked. Give him a call.

funkstuf
04-12-2016, 12:00 PM
Here is what the bad springs look like. Good springs have evenly spaced coils.

Here are my springs. One looks worse than the other, but I also noticed that if I depress the one that looks the best it seems to have a lot of play in the hole and doesn't return with the copper end in a centered position.4146041461

funkstuf
04-12-2016, 12:01 PM
Josh at DPI was able to sell me a set of butterflies with good springs. I'm not sure if they were reconditioned or just good used parts, but they worked. Give him a call.
Thanks, My springs don't look good so I'll talk to Josh at DPI.

Bitsyncmaster
04-12-2016, 01:22 PM
Here are my springs. One looks worse than the other, but I also noticed that if I depress the one that looks the best it seems to have a lot of play in the hole and doesn't return with the copper end in a centered position.4146041461

Yes those springs are most likely the cause of your problem. You can just seal up the holes in the plates but then you get pretty bad under shoot of the idle RPM.

funkstuf
04-12-2016, 01:36 PM
Yes those springs are most likely the cause of your problem. You can just seal up the holes in the plates but then you get pretty bad under shoot of the idle RPM.

Yes, and I think I read that you had worked on that on your programmable ECU. Did you get that perfected? I read another post where a guy took the springs out and plugged the hole, then bent the micro-switch so it would activate on before complete De-throttled and he said this seemed to take care of the undershoot by allowing the idle motor to turn on at the end of the deceleration.

Bitsyncmaster
04-12-2016, 02:18 PM
Yes, and I think I read that you had worked on that on your programmable ECU. Did you get that perfected? I read another post where a guy took the springs out and plugged the hole, then bent the micro-switch so it would activate on before complete De-throttled and he said this seemed to take care of the undershoot by allowing the idle motor to turn on at the end of the deceleration.

Good memory:):)

I have been running the blocked holes in the throttle plates for two years but I still occasionally get an under shoot more than I like. I decided I would go back to the OEM setup with the springs rather than put more effort into the software. Now if there was no source for good throttle assemblies, I would put more effort into the software changes.

funkstuf
04-12-2016, 04:17 PM
Good memory:):)

I have been running the blocked holes in the throttle plates for two years but I still occasionally get an under shoot more than I like. I decided I would go back to the OEM setup with the springs rather than put more effort into the software. Now if there was no source for good throttle assemblies, I would put more effort into the software changes.

Thanks, rather than plug the holes I think I'll just order the refurbished throttle body from DPI and send the core to them.
I think this will solve it and appreciate your help. I'll post the results once I get it in.

cdrusn
05-14-2016, 06:45 PM
Did you ever get the rebuilt throttle bodies in? :race:

Giamanut
10-30-2019, 10:33 PM
I've been fiddling with an idle problem for awhile now and hoped to get it solved, but here I am. Typically idles high. When I start the car it's about 1000 rpm and when it warms up after a few minutes goes to 14-1500 rpm. I backed off the microswitch and idle screw but it stayed at high idle. I also checked the microswitch to ground and it is working properly.

I disconnected inner bulkhead on ECU and it goes to 2500. Unplugging the outer does not change anything. I tested the thermistor on the 4 pin bulkhead at the ECU and found resistance so assumed it's working. I also swapped it with another ECU I have that is known good and had the same results.

I checked around injectors and vacuum lines with carb fluid but didn't spot any leaks.
I checked the idle motor and it does hum. Also, just for good measure took it out and sprayed carb fluid in it and shook it around a bit. At one point I checked voltages on the idle motor connector and noticed 12 volts center pin, about 10 volts to one side but 0 volts to the other. I assumed that it was just not signaling one side at the time. The Lambda system does buzz.

I tested the Lambda Dwell with the engine warmed and the O2 sensor disconnected and got 44. (Using Orange wire and ground on the engine ground on the intake 4 cylinder mode)
The engine idles around 850 rpm with O2 sensor disconnected.

When I connect the O2 sensor the idle goes up to 14-1500 rpm and here's the disturbing part. The Dwell goes to about 84. I messed a bit with the air/fuel screw on the distributor and I can get the RPMs to drop to 800 but it smells like it's running to rich and wants to flood so I put it back the way it was. Also, that didn't seem to change the Dwell with the O2 sensor hooked up and I understand that it should be around 40, not 84.

In any case, the Lambda system is working very hard when the O2 sensor is hooked up.
Questions:
1.) Could a bad O2 sensor cause this because it does seem to be working.
2.) I didn't check continuity on all ECU lines, but unhooking it didn't seem to matter. I did consider that the motor might just stay in the state it was left in, and perhaps if one side's not working
3.) Any other ideas based on what I've done so far?
It really sounds like your air idle motor is is letting air by when it should not be. Try taking it out and plugging the lines use your thumb over the pipe of agony side and you can modulate the idle. If it is stuck open it is an vacuum leak.

Giamanut
10-30-2019, 10:41 PM
It really sounds like your air idle motor is is letting air by when it should not be. Try taking it out and plugging the lines use your thumb over the pipe of agony side and you can modulate the idle. If it is stuck open it is an vacuum leak.
Also if you dwell goes up with the O2 sensor plugged in that means it is adding fuel because there is extra air. Extra air and fuel = more RPM! you System is working correct. When the O2 sensor is disconnected and you idle goes to 800 I am guessing you will see your engine temp go up because it is on the lean side! Don't want to be there!