Surging, and Almost stall out when at idle
04-25-09, 08:36 AM
#1
RIP IceMark
Thread Starter
iTrader: (7)
Join Date: Oct 2007
Location: Somerville, NJ
Posts: 380
Likes: 0
Received 0 Likes
on
0 Posts
Surging, and Almost stall out when at idle
Ok,
Car won't idle all the time.
Sometimes it idles fine..
But usually when driving.. it goes up.... and then surges down..
Always after in gear and putting it back in neutral
The rpms drop so bad it almost stalls out...
and I sit at the traffic light like I have a bridge port on low rpms...
It surges from like 200-1200 rpm.
Sometimes the car even shuts off
When I'm driving... car acts Totally normal nothing wrong.. high boost etc..
Just very shameful when sitting at a stop light..
anyone's 2 cents?
I have a wideband and AVC-R to monitor it.. and power FC also..
Car won't idle all the time.
Sometimes it idles fine..
But usually when driving.. it goes up.... and then surges down..
Always after in gear and putting it back in neutral
The rpms drop so bad it almost stalls out...
and I sit at the traffic light like I have a bridge port on low rpms...
It surges from like 200-1200 rpm.
Sometimes the car even shuts off
When I'm driving... car acts Totally normal nothing wrong.. high boost etc..
Just very shameful when sitting at a stop light..
anyone's 2 cents?
I have a wideband and AVC-R to monitor it.. and power FC also..
04-25-09, 05:55 PM
#4
Junior Member
Join Date: Apr 2009
Location: Indian River Florida
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
I have a power FC/single turbo setup and nobody has ben able to get the IAC to work properly, we unpluged it and set the idle with the set scerw. It works so good we forget about it.
04-26-09, 01:18 AM
#6
A properly working ISC idles far better than not having one, especially if you don't want your car idling near 1000rpm. The idle is way less sensitive to changes in engine vacuum or drag from A/C or accessories. It fluctuates far less with changes in the weather. It reduces the chance of stalling on decel. Mazda put the system there for a reason. Many owners are not bothered by these driveability problems, or they don't notice them at all, or they idle the car so high that the symptoms don't even show up.
But running no ISC annoys the hell out of me, especially when my daily driver never has idle stumbles.
But running no ISC annoys the hell out of me, especially when my daily driver never has idle stumbles.
04-26-09, 02:59 PM
#7
Junior Member
Join Date: Apr 2009
Location: Indian River Florida
Posts: 34
Likes: 0
Received 0 Likes
on
0 Posts
I wish someone could fix the IAC. As soon as we installed the power FC the car surges till it almost stops running and then to almost 18-2000 RPS's. I have checked for vacume leaks and basic stuff and had it to "RX7 people" with power FC expierience, spent time and money with no luck. look forward to checking any old notes and sharing them with my "RX7 guy".
Trending Topics
04-26-09, 03:38 PM
#8
I posted this in another thread responding to similar idle type of complaints, so I will post it again. It is a systematic discussion of the causes of idle sticking/surging, the tools needed to solve it, and the tuning procedure needed to solve it. I have personally gotten a street ported FD to idle at the target 850 idle speed using the ISC, with no sticking or surging 95% of the time (idle may fluctuate briefly as the PFC adjusts to a significant weather change).
Original thread: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/unknown-idle-temp-bucking-issue-89%2Ac-833989/
"Assuming no mechanical problems with the car, this problem WILL NOT be solved without a datalogit, a wideband, some street tuning, and a lot of time on your hands. So go buy a datalogit. Yes, I know you just paid someone to tune your car, but buy one anyway if you don't have it. The PFC idle control circuit is very sensitive, but it DOES do a good job if you get it set up right. Many people remove the ISC and disable PFC timing control. When you do that, you lose A/C and electrical load idle up, as well as increase the chance of the car stalling on decel. But I have gotten the PFC idle system to work right before, it's just a tedious process.
As far as your situation goes, I have encountered temperature-related surging. It is was on my friend's FD which I tuned, streetported with stock sequential twins (550/1300) and stock vacuum routing. airpump was removed, but I think the ACV was hooked up... I didn't do the vac job. Assuming there are no vacuum leaks and the ISC isn't dirty/bad, idle surging on a PFC is usually caused by
1) lean condition, especially on hot starts (which is what you are having). lean condition is usually leaner than 13-13.5:1, measured with a wideband on a car with no airpump. This is a function of IAT correction and the INJ map in the PFC, especially under the low vacuum areas usually reached during a hot start.
2) too much bypass air. This is a function of TB adjustment (primary TB bore butterfly stop screw, secondary TB bore stop screw, air adjust screw) and the idle learning procedure. Of course a tight throttle cable can throw things off too, the spec is 1-2mm of freeplay. I measure freeplay in the cable by marking the cable with a piece of masking tape and measuring the freeplay with a dial caliper.
3) O2 feedback being turned on without a functioning airpump and careful tuning.
In the case of this particular car I was working on, it would warm up and after the fast idle cam disengaged the idle would cut down to right around the target set in the PFC. Then at temperatures in the high 80s C or any time electrical load was detected (fan relay switch point in the PFC especially) the idle would freak out. The car would surge, especially on decel or hot start, and usually the idle would stick at around 1200 or so despite the target being set in the 800 range.
Solving this problem took about 12 hours of trial and error. Several NC rotary shops had taken a stab at it and didn't solve it during the limited time period they had. If it really is just a tuning/TB adjustment issue, the only way a shop could solve it would be with a blank check for however much hourly work it would take.
Anyway, the first step is to begin adjusting the TB screws. You can PM cewrx7r1 , he sells a PFC tuning document which covers TB adjustment in more detail. The first thing everybody does, besides checking the throttle cable and fast idle cam, is tighten down the screw under the lower studs of the TB elbow. It's recessed in there. You tighten that all the way and back it out 1/2 turn.
Set your idle speeds in the PFC. I prefer to set my base idle speed and electrical load idle speed to the same value, and I set the fuel cut recovery to 1500. My idle settings on that FD:
F/C AE 1500
F/C EL 1500
F/C AC 1500
Idle AE 850
Idle EL 850
Idle AC 950
The EL detector switches on any time the fans switch on, in addition the headlights and blower motor. The fan relay (and E/L indicator in the PFC) switches on at 1 C below the target temp in Settings 3 of the FC edit software. This is just speculation here, but if your tuner set the fans to come on at 90 C, the E/L detector comes on (you can see this on the commander inputs screen under the "etc" menu) and the ISC circuit will react differently. Base timing advances from -5 advance to about +6, and the car can start flipping out then too. Even if the E/L detector doesn't come on, the PFC idle control circuit is very sensitive (even to temperature) as I said, especially when there is too much bypass air.
Anyway, after resetting the PFC (unless it's possible to do the idle learn without a reset) make sure that O2 feedback is off and your idle speeds are set. Now start the car and perform the idle learn procedure where you idle for 10 minutes with no load, then 10 minutes with E/L, and 10 minutes with A/C. Check that your idle AFR's range never get leaner than 13:1 in this case. Sometimes leaner will work, but we'll set the upper acceptable limit here to 12.9:1 . Since there is no O2 sensor correction, the AFR will fluctuate with ambient conditions, and I usually aim for a range of 12.2-12.9:1 . Don't touch anything until the learn procedure is done, even if the idle is rough while the PFC is learning.
When the procedure is done, drive it around town for about 30 minutes, as the PFC will continue to learn as you drive. Monitor the AFR's, and if they get too lean you need to adjust the INJ map and/or the IAT correction map. See if any sticking or surging improves. The idle may stick high on decel, until vehicle speed is below something like 5-10 km/h. That is the ISC preventing a stall. It should slowly drop down to the target idle speed however once the car reaches a complete stop.
If the idle is still sticking or surging after all this, and you are positive there are no ISC problems or vacuum leaks, you have to adjust idle air and fuel further. If the AFR's are fine, you will have to mess with the TB again. Tighten the air adjust screw (recessed under the TB elbow) all the way and back out to 1/4 turn, at least if you had it set to 1/2 turn before. Don't close it all the way. Now loosen the primary bore stop screw (on the front of the TB) slightly to close the throttle plates. Double check that the fast idle cam is fully disengaged when the car is warm.
Now perform the idle learning procedure again (all 30 minutes of it). Assuming no other issues with the car, repeat the process over and over again, reducing bypass air until the idle settles down. If you reduce by bypass air a bit too much, you may have some stalling on decel unless you add more bypass air back or adjust the dashpot. And again, if you don't have a wideband, a datalogit (with some basic knowledge of how to use it), and 12 hours of your life, don't expect to get the idle right. If you want the most help from us here, wire in a wideband's output to the datalogit, and start posting AFR logs of you driving around. (also double check that all sensors are in spec"
Air adjust screw:
butterfly adjustment screws:
Original thread: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/unknown-idle-temp-bucking-issue-89%2Ac-833989/
"Assuming no mechanical problems with the car, this problem WILL NOT be solved without a datalogit, a wideband, some street tuning, and a lot of time on your hands. So go buy a datalogit. Yes, I know you just paid someone to tune your car, but buy one anyway if you don't have it. The PFC idle control circuit is very sensitive, but it DOES do a good job if you get it set up right. Many people remove the ISC and disable PFC timing control. When you do that, you lose A/C and electrical load idle up, as well as increase the chance of the car stalling on decel. But I have gotten the PFC idle system to work right before, it's just a tedious process.
As far as your situation goes, I have encountered temperature-related surging. It is was on my friend's FD which I tuned, streetported with stock sequential twins (550/1300) and stock vacuum routing. airpump was removed, but I think the ACV was hooked up... I didn't do the vac job. Assuming there are no vacuum leaks and the ISC isn't dirty/bad, idle surging on a PFC is usually caused by
1) lean condition, especially on hot starts (which is what you are having). lean condition is usually leaner than 13-13.5:1, measured with a wideband on a car with no airpump. This is a function of IAT correction and the INJ map in the PFC, especially under the low vacuum areas usually reached during a hot start.
2) too much bypass air. This is a function of TB adjustment (primary TB bore butterfly stop screw, secondary TB bore stop screw, air adjust screw) and the idle learning procedure. Of course a tight throttle cable can throw things off too, the spec is 1-2mm of freeplay. I measure freeplay in the cable by marking the cable with a piece of masking tape and measuring the freeplay with a dial caliper.
3) O2 feedback being turned on without a functioning airpump and careful tuning.
In the case of this particular car I was working on, it would warm up and after the fast idle cam disengaged the idle would cut down to right around the target set in the PFC. Then at temperatures in the high 80s C or any time electrical load was detected (fan relay switch point in the PFC especially) the idle would freak out. The car would surge, especially on decel or hot start, and usually the idle would stick at around 1200 or so despite the target being set in the 800 range.
Solving this problem took about 12 hours of trial and error. Several NC rotary shops had taken a stab at it and didn't solve it during the limited time period they had. If it really is just a tuning/TB adjustment issue, the only way a shop could solve it would be with a blank check for however much hourly work it would take.
Anyway, the first step is to begin adjusting the TB screws. You can PM cewrx7r1 , he sells a PFC tuning document which covers TB adjustment in more detail. The first thing everybody does, besides checking the throttle cable and fast idle cam, is tighten down the screw under the lower studs of the TB elbow. It's recessed in there. You tighten that all the way and back it out 1/2 turn.
Set your idle speeds in the PFC. I prefer to set my base idle speed and electrical load idle speed to the same value, and I set the fuel cut recovery to 1500. My idle settings on that FD:
F/C AE 1500
F/C EL 1500
F/C AC 1500
Idle AE 850
Idle EL 850
Idle AC 950
The EL detector switches on any time the fans switch on, in addition the headlights and blower motor. The fan relay (and E/L indicator in the PFC) switches on at 1 C below the target temp in Settings 3 of the FC edit software. This is just speculation here, but if your tuner set the fans to come on at 90 C, the E/L detector comes on (you can see this on the commander inputs screen under the "etc" menu) and the ISC circuit will react differently. Base timing advances from -5 advance to about +6, and the car can start flipping out then too. Even if the E/L detector doesn't come on, the PFC idle control circuit is very sensitive (even to temperature) as I said, especially when there is too much bypass air.
Anyway, after resetting the PFC (unless it's possible to do the idle learn without a reset) make sure that O2 feedback is off and your idle speeds are set. Now start the car and perform the idle learn procedure where you idle for 10 minutes with no load, then 10 minutes with E/L, and 10 minutes with A/C. Check that your idle AFR's range never get leaner than 13:1 in this case. Sometimes leaner will work, but we'll set the upper acceptable limit here to 12.9:1 . Since there is no O2 sensor correction, the AFR will fluctuate with ambient conditions, and I usually aim for a range of 12.2-12.9:1 . Don't touch anything until the learn procedure is done, even if the idle is rough while the PFC is learning.
When the procedure is done, drive it around town for about 30 minutes, as the PFC will continue to learn as you drive. Monitor the AFR's, and if they get too lean you need to adjust the INJ map and/or the IAT correction map. See if any sticking or surging improves. The idle may stick high on decel, until vehicle speed is below something like 5-10 km/h. That is the ISC preventing a stall. It should slowly drop down to the target idle speed however once the car reaches a complete stop.
If the idle is still sticking or surging after all this, and you are positive there are no ISC problems or vacuum leaks, you have to adjust idle air and fuel further. If the AFR's are fine, you will have to mess with the TB again. Tighten the air adjust screw (recessed under the TB elbow) all the way and back out to 1/4 turn, at least if you had it set to 1/2 turn before. Don't close it all the way. Now loosen the primary bore stop screw (on the front of the TB) slightly to close the throttle plates. Double check that the fast idle cam is fully disengaged when the car is warm.
Now perform the idle learning procedure again (all 30 minutes of it). Assuming no other issues with the car, repeat the process over and over again, reducing bypass air until the idle settles down. If you reduce by bypass air a bit too much, you may have some stalling on decel unless you add more bypass air back or adjust the dashpot. And again, if you don't have a wideband, a datalogit (with some basic knowledge of how to use it), and 12 hours of your life, don't expect to get the idle right. If you want the most help from us here, wire in a wideband's output to the datalogit, and start posting AFR logs of you driving around. (also double check that all sensors are in spec"
Air adjust screw:
butterfly adjustment screws:
Thread
Thread Starter
Forum
Replies
Last Post
The1Sun
1st Generation Specific (1979-1985)
7
09-18-15 07:13 PM
RotaryBobby
1st Generation Specific (1979-1985)
1
09-10-15 01:33 PM
