fluctuating idle
11-06-2016, 06:23 PM
#1
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fluctuating idle
i have 100 miles on my new build and have an issue with my idle. no fast idle when cold and when warmed up the idle bounces between 800 and 1000. when coming to a stop the idle hovers around 1000 and after a couple of seconds drops down to around 800. solomons tune set the idle to around 750. car runs great otherwise. is it suppose to fast idle when cold? where do i start?
11-06-2016, 08:59 PM
#2
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Re: fluctuating idle
Yes, stock programming sets target idle speed based on coolant temp sensor. Stock M6 idle is 800 RPM, fully warmed up. As high as 1,200 RPM when very cold. Odd that he set it below stock. Typically the stock tach reads 100-200 RPM higher than actual. You need a scanner to read actual RPM direct from the PCM.
Also normal for idle to hold high until the vehicle comes to a full stop. As the vehicle starts to move, the PCM starts to open up the IAC to keep the engine from stalling if the throttle suddenly closes.
Also normal for idle to hold high until the vehicle comes to a full stop. As the vehicle starts to move, the PCM starts to open up the IAC to keep the engine from stalling if the throttle suddenly closes.
11-06-2016, 10:30 PM
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Re: fluctuating idle
thanks for the reply. ok so from what you are telling me it sounds like its doing what its suppose to do. the only thing is that it does not fast idle when cold. i have to hit the gas a bit or else it will stall. any way to correct that? i have the 94/95 scan program installed on my computer but have not used it yet.
11-07-2016, 04:19 PM
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Re: fluctuating idle
Check what temp the coolant temp sensor is reporting to the PCM. If the PCM doesn't know the engine is cold, it can't richen the mixture for cold start, or elevate the idle. I guess it's possible the tuner altered the tables of idle speed vs. coolant temp, but I don't know why. Might be worth asking him if there is anything in the tune that would cause this.
Scan9495 will tell you the target idle speed and the actual idle speed. Will give you numbers to compare with your tach readings. It will allow you to see how the IAC counts respond to any variance between the target and actual idle RPM.
Scan9495 will tell you the target idle speed and the actual idle speed. Will give you numbers to compare with your tach readings. It will allow you to see how the IAC counts respond to any variance between the target and actual idle RPM.
11-07-2016, 10:33 PM
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Re: fluctuating idle
i do not think the tuner altered the tables. as soon as i can i will do a scan to see what the values are. would it be ok to PM you a copy so you could look at it ? thanks for the imput- guys like you that know a lot and are willing to take the time to help others are rare. thanks Al
11-07-2016, 11:26 PM
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Re: fluctuating idle
I'll look at the file. Include it as an attachment in a reply post in this thread.
Click on "Go Advanced" button under the message field. That will add options below the message field. Click on "Manage Attachments" and attach the .csv file.
I can generally download the file the day you post it, take a quick look at it, reply the next day. If it needs a more in-depth review it can take a few days to get back to you. I have a backlog of a few files for review.
Click on "Go Advanced" button under the message field. That will add options below the message field. Click on "Manage Attachments" and attach the .csv file.
I can generally download the file the day you post it, take a quick look at it, reply the next day. If it needs a more in-depth review it can take a few days to get back to you. I have a backlog of a few files for review.
11-23-2016, 01:47 PM
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Re: fluctuating idle
Idle programming is 850 RPM up 72*F and 800 RPM at 149*. The PCM interpolates the target idle speed in 12.5 RPM increments, so from 850 RPM at 72*F, the target drops to 838, 825, 812, 800 as the temperature moves from 72*F to 149*F
Engine starts with an idle of 1,442 RPM and the IAC at 107 counts. The PCM then starts pulling the IAC counts down to try and meet the 850 RPM target idle speed. It takes a long time, and has to get the IAC counts down to 51 to get anywhere near the target. Stock programming calls for 900 RPM up to 89*F, and drops to 800 RPM at 111*F.
This seems to contradict your statement that there is "no fast idle when cold".
The engine seems to warm up very slowly. Are you running a thermostat? Normally the PCM will go into closed loop after 206 seconds. But only if the O2 sensors are hot and the coolant is reasonable warm. Your O2 sensors are "ready" per the flags in the data log, but at 206 seconds, the coolant is only at 108*F. Eventually it goes into closed loop at 338 seconds, coolant temp at 140*F. I don't know if the programmer can change the parameters for entering closed loop.
Once it's in closed loop, the coolant has still not reached the 149*F that appears to be the programmed value for starting the drop to 800 RPM. When it finally reaches the 149*F point, the target idle is 800 RPM, and the variation above and below that RPM is not unreasonable for a more aggressive cam (126/126 112 LSA 0.520/0.520). Where the stock cam will generally produce an RPM variation of +/- 25 RPM above and below the target idle speed, yours is closer to +/-50 RPM. At no time while the TP% is at 0% does the idle get anywhere near 1,000 RPM. There are a couple of places where there is a 100 RPM surge, but in the high 800's.
Eventually, is appears you started blipping the throttle. Engine RPM obviously increases, and slowly comes back down like it should, although maybe a bit too slowly. Almost seems like the IAC responds too slowly to high RPM, just as it did from cold start.
The mystery here is that while you were blipping the throttle, the MPH started jumping around, in strange ways. Was the car actually moving? For example, MPH shows "0", than in 1/10th of a second jumps to 1 MPH and in the next 1/10th of a second jumps to 18 MPH and in the next 1/10th drops to 10 MPH and in the fourth 1/20th drops back to 0. Hard to believe the car could really do that. This happens twice in the data log, and makes me wonder if you have some sort of electrical interference with the wiring from the VSS. This is significant, because the IAC counts can be affected by the fact that the PCM thinks the car is moving, by increasing the IAC counts. That would slow down the ability of the PCM to bring the RPM down to target idle speed after the throttle closes.
Might be worth checking the IAC system to make sure the 52mm throttle body is allowing enough idle air to enter, and the IAC motor pintle is not dirty, or the passages partially plugged. There is no real evidence of split BLM's at idle (common with aftermarket TB's). Idle cell #16 left BLM is 130 (adding 1.6% extra fuel) and right BLM is 135 (adding 5.5%).
Engine starts with an idle of 1,442 RPM and the IAC at 107 counts. The PCM then starts pulling the IAC counts down to try and meet the 850 RPM target idle speed. It takes a long time, and has to get the IAC counts down to 51 to get anywhere near the target. Stock programming calls for 900 RPM up to 89*F, and drops to 800 RPM at 111*F.
This seems to contradict your statement that there is "no fast idle when cold".
The engine seems to warm up very slowly. Are you running a thermostat? Normally the PCM will go into closed loop after 206 seconds. But only if the O2 sensors are hot and the coolant is reasonable warm. Your O2 sensors are "ready" per the flags in the data log, but at 206 seconds, the coolant is only at 108*F. Eventually it goes into closed loop at 338 seconds, coolant temp at 140*F. I don't know if the programmer can change the parameters for entering closed loop.
Once it's in closed loop, the coolant has still not reached the 149*F that appears to be the programmed value for starting the drop to 800 RPM. When it finally reaches the 149*F point, the target idle is 800 RPM, and the variation above and below that RPM is not unreasonable for a more aggressive cam (126/126 112 LSA 0.520/0.520). Where the stock cam will generally produce an RPM variation of +/- 25 RPM above and below the target idle speed, yours is closer to +/-50 RPM. At no time while the TP% is at 0% does the idle get anywhere near 1,000 RPM. There are a couple of places where there is a 100 RPM surge, but in the high 800's.
Eventually, is appears you started blipping the throttle. Engine RPM obviously increases, and slowly comes back down like it should, although maybe a bit too slowly. Almost seems like the IAC responds too slowly to high RPM, just as it did from cold start.
The mystery here is that while you were blipping the throttle, the MPH started jumping around, in strange ways. Was the car actually moving? For example, MPH shows "0", than in 1/10th of a second jumps to 1 MPH and in the next 1/10th of a second jumps to 18 MPH and in the next 1/10th drops to 10 MPH and in the fourth 1/20th drops back to 0. Hard to believe the car could really do that. This happens twice in the data log, and makes me wonder if you have some sort of electrical interference with the wiring from the VSS. This is significant, because the IAC counts can be affected by the fact that the PCM thinks the car is moving, by increasing the IAC counts. That would slow down the ability of the PCM to bring the RPM down to target idle speed after the throttle closes.
Might be worth checking the IAC system to make sure the 52mm throttle body is allowing enough idle air to enter, and the IAC motor pintle is not dirty, or the passages partially plugged. There is no real evidence of split BLM's at idle (common with aftermarket TB's). Idle cell #16 left BLM is 130 (adding 1.6% extra fuel) and right BLM is 135 (adding 5.5%).
11-23-2016, 07:33 PM
#13
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Re: fluctuating idle
i blipped the throttle once or twice when i first started it up because it seemed like it would stall. did not hit the gas after that nor did i move the car. have a 160 thermostat.
11-25-2016, 11:19 AM
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Re: fluctuating idle
Really strange.... there were at least 1/2-dozen times in the first 338 seconds, before it went into closed loop where the throttle voltage and % were moving around, and RPM was increasing. That may have been what you indicate above.
But at 448 seconds, the throttle starts to move again, reaching a max of 30% and RPM maxes at 3,985. In the last two frames of data, the MPH indicate 8 and 10 MPH.
At 451 seconds, in 4 frames of data the TP% goes 15%, 26%, 26% and 9%. In the fourth frame of data, the MPH goes to 10, then in the next three frames to 13 MPH, 8 MPH and 1 MPH. In that short period of time (less than 1/2 second) RPM goes from 2,286 to 4,183 and back down to 3,347 - IS THAT THE KIND OF SURGE YOU ARE SEEING, WITH NO TOUCH OF THE THROTTLE, CAR AT A COMPLETE STANDSTILL?.
Then at 452 seconds, the throttle is fluttering between 1% and 8% for a period of 13.8 seconds, and the RPM increases from 1,739 to 2,435. During this period, no MPH reading. Then at the end of that fluttering, the throttle instantly goes to 18%, then to 64% in the next 1/10th second and the RPM goes from 2,464 to 4,318 RPM. And the MPH in a period of 3/10ths of a second indicate 1 MPH, 18 MPH, 10 MPH.
If that is what you are calling "fluctuating idle", it is nothing like anything I have ever seen before. It's like the throttle is opening itself.... TP% increases, MAP increases, MAF increases, and RPM increases. But you indicate you are not touching it. If it was floating around 1-5% I could see it as possibly a loose spring on the throttle return, but for the throttle to open to 64% would seem more like it is possessed by demons.... LOL.
But at 448 seconds, the throttle starts to move again, reaching a max of 30% and RPM maxes at 3,985. In the last two frames of data, the MPH indicate 8 and 10 MPH.
At 451 seconds, in 4 frames of data the TP% goes 15%, 26%, 26% and 9%. In the fourth frame of data, the MPH goes to 10, then in the next three frames to 13 MPH, 8 MPH and 1 MPH. In that short period of time (less than 1/2 second) RPM goes from 2,286 to 4,183 and back down to 3,347 - IS THAT THE KIND OF SURGE YOU ARE SEEING, WITH NO TOUCH OF THE THROTTLE, CAR AT A COMPLETE STANDSTILL?.
Then at 452 seconds, the throttle is fluttering between 1% and 8% for a period of 13.8 seconds, and the RPM increases from 1,739 to 2,435. During this period, no MPH reading. Then at the end of that fluttering, the throttle instantly goes to 18%, then to 64% in the next 1/10th second and the RPM goes from 2,464 to 4,318 RPM. And the MPH in a period of 3/10ths of a second indicate 1 MPH, 18 MPH, 10 MPH.
If that is what you are calling "fluctuating idle", it is nothing like anything I have ever seen before. It's like the throttle is opening itself.... TP% increases, MAP increases, MAF increases, and RPM increases. But you indicate you are not touching it. If it was floating around 1-5% I could see it as possibly a loose spring on the throttle return, but for the throttle to open to 64% would seem more like it is possessed by demons.... LOL.
11-25-2016, 01:16 PM
#15
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Re: fluctuating idle
yes it definitely is strange. i blipped the throttle in the first couple of seconds and never touched it after that. its odd that starting at the 448 second mark the TP% is all over the place when actually the engine is idling and never goes over 1000 - 1200 rpm even though it shows 2,3 or 4k rpm. the car never moved throughout the entire scan? when i say the idle was fluctuating i meant after its warm it alternates between 800 and 1100. can that be the norm for my cam 225/112/565 ? where should i start checking -- TPS ? IAC ?