New MAF CO tuning and Stalling and Rough idle problem
02-24-2013, 01:36 AM
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New MAF CO tuning and Stalling and Rough idle problem
1986 928S 32V 112k miles
I got a rebuilt MAF from 928srus. My previous MAF was running way out of spec, with the resistance maxed out >1kOhm and the car was still running rich, so I figured that the MAF needed to be replaced at some point anyway.
I have a similar "rough idle" problem to other '86 928s, but once I can stabilize an idle, it will do it just fine (see below).
Anyway, I was doing the CO/Idle adjustment per this post:
https://rennlist.com/forums/928-foru...5-86-us-3.html
I couldn't get the CO reading test to make any sense, and I think I have another problem as well related to the stalling out. The new unit shipped at 382Ohms and when I let the car and O2 sensor warm up the LED was on, so I leaned it out a little. I kept going to about 200Ohm and still, couldn't get it to turn off. I then when back to 382Ohms and the light was OFF. After about a minute of running, the light turned on again and then I tried to lean it out once again but couldn't get it in the right range.
Rough Idle/Stalling:
What was really puzzling me is the issue of the bridging B->C. Whenever I flip the switch, the car revs, sputters and dies. I open the circuit once more, start the car. If I don't immediately give it gas when I start it, it will die. If I slowly let off of the gas into idle, it will idle fine.
Furthermore if I'm driving and I let into the clutch and let off the gas quickly, I the car will stall, scaring my passenger usually. It used to do this even before I put the new MAF in there, but after I put the new MAF (and disconnected the battery for a bit) it's doing this more frequently.
I have been searching through old posts and the WSM, but I haven't found anything that helps me diagnose this problem. Has anyone had experience with similar problems? I'm pretty new to a lot of this stuff, and I find the directions in the WSM hard to find and hard to follow, so any additional explanations would be welcome! Feel free to request pictures/measurements/etc.
Thanks in advance
I got a rebuilt MAF from 928srus. My previous MAF was running way out of spec, with the resistance maxed out >1kOhm and the car was still running rich, so I figured that the MAF needed to be replaced at some point anyway.
I have a similar "rough idle" problem to other '86 928s, but once I can stabilize an idle, it will do it just fine (see below).
Anyway, I was doing the CO/Idle adjustment per this post:
https://rennlist.com/forums/928-foru...5-86-us-3.html
I couldn't get the CO reading test to make any sense, and I think I have another problem as well related to the stalling out. The new unit shipped at 382Ohms and when I let the car and O2 sensor warm up the LED was on, so I leaned it out a little. I kept going to about 200Ohm and still, couldn't get it to turn off. I then when back to 382Ohms and the light was OFF. After about a minute of running, the light turned on again and then I tried to lean it out once again but couldn't get it in the right range.
Rough Idle/Stalling:
What was really puzzling me is the issue of the bridging B->C. Whenever I flip the switch, the car revs, sputters and dies. I open the circuit once more, start the car. If I don't immediately give it gas when I start it, it will die. If I slowly let off of the gas into idle, it will idle fine.
Furthermore if I'm driving and I let into the clutch and let off the gas quickly, I the car will stall, scaring my passenger usually. It used to do this even before I put the new MAF in there, but after I put the new MAF (and disconnected the battery for a bit) it's doing this more frequently.
I have been searching through old posts and the WSM, but I haven't found anything that helps me diagnose this problem. Has anyone had experience with similar problems? I'm pretty new to a lot of this stuff, and I find the directions in the WSM hard to find and hard to follow, so any additional explanations would be welcome! Feel free to request pictures/measurements/etc.
Thanks in advance
02-24-2013, 04:09 AM
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Right, I don't want to go super far out of spec, I'm curious as to why it's too rich when I'm running down to 200Ohms? Are there other things I should check for before relying on the CO pot adjustment. Idle (when stable) is roughly 690RPM
02-24-2013, 09:20 PM
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Ok everyone, here is an update.
I realized that the Idle Air Valve was turned basically all the way to the right, being totally "closed." This was the only way to get my idle down to around 680RPMs. The dying out problem was basically because the engine was not getting enough air at idle. This is whhy it would die out with the B->C switch ON or when I let off the accelerator quickly.
I backed the idle air valve, increasing idle speed and the engine revved a bit. The problem now is summarized as this:
A) When I flip the B->C switch OFF (open), idle stabilizes...but at 900 RPM. If RPM is any LOWER and it'll die out only when I let off the throttle quickly during operation.
B) When I flip the B->C switch ON (closed), idle jumps around but does not die out! I can not get idle to stabilize at one RPM range.
C) The MAF is now tuned in at this higher RPM range (a little richer than stock, 404Ohms), I did this the best that I could, because the idle jumps around a bit, but it mostly stays at blinking until it dips or revs.
D) Engine now dies out on warm start.
Also today I cleaned the LH plug contact switch, tested throttle position sensor and temp II. I have not done a totally cold start, but I will keep everyone updated on what happens tomorrow morning.
I realized that the Idle Air Valve was turned basically all the way to the right, being totally "closed." This was the only way to get my idle down to around 680RPMs. The dying out problem was basically because the engine was not getting enough air at idle. This is whhy it would die out with the B->C switch ON or when I let off the accelerator quickly.
I backed the idle air valve, increasing idle speed and the engine revved a bit. The problem now is summarized as this:
A) When I flip the B->C switch OFF (open), idle stabilizes...but at 900 RPM. If RPM is any LOWER and it'll die out only when I let off the throttle quickly during operation.
B) When I flip the B->C switch ON (closed), idle jumps around but does not die out! I can not get idle to stabilize at one RPM range.
C) The MAF is now tuned in at this higher RPM range (a little richer than stock, 404Ohms), I did this the best that I could, because the idle jumps around a bit, but it mostly stays at blinking until it dips or revs.
D) Engine now dies out on warm start.
Also today I cleaned the LH plug contact switch, tested throttle position sensor and temp II. I have not done a totally cold start, but I will keep everyone updated on what happens tomorrow morning.
02-25-2013, 05:03 PM
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Started the car up cold this morning...socal weather was like ~55->60 degrees.
It started right up and did not die out...even without giving it any gas.
It idle VERY roughly, centered at about 600-700RPM judging by the tach.
As the car warmed up, and after a quick drive around the neighborhood flipping in the clutch to check the idle, the idle INCREASED and the idle STABILIZED.
As the car warmed up to the first white notch, it was idling at 950RPM-1000RPM (again, tach) and very stable.
It started right up and did not die out...even without giving it any gas.
It idle VERY roughly, centered at about 600-700RPM judging by the tach.
As the car warmed up, and after a quick drive around the neighborhood flipping in the clutch to check the idle, the idle INCREASED and the idle STABILIZED.
As the car warmed up to the first white notch, it was idling at 950RPM-1000RPM (again, tach) and very stable.
02-25-2013, 05:24 PM
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At 100K+ miles, if the ISV/IAC is original, then it needs replacing.
It will usually wear more one way than the other. IE. open, high idle, or close, low idle.
Check all the intake boots clamps. Replace if oil soaked/squishy.
Check at the LH that the WOT and idle inputs are working (ground).
No idle contact will make it idle high.
(EZF and LH2.2 pinouts)
It will usually wear more one way than the other. IE. open, high idle, or close, low idle.
Check all the intake boots clamps. Replace if oil soaked/squishy.
Check at the LH that the WOT and idle inputs are working (ground).
No idle contact will make it idle high.
(EZF and LH2.2 pinouts)
02-25-2013, 07:39 PM
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At 100K+ miles, if the ISV/IAC is original, then it needs replacing.
It will usually wear more one way than the other. IE. open, high idle, or close, low idle.
Check all the intake boots clamps. Replace if oil soaked/squishy.
Check at the LH that the WOT and idle inputs are working (ground).
No idle contact will make it idle high.
(EZF and LH2.2 pinouts)
It will usually wear more one way than the other. IE. open, high idle, or close, low idle.
Check all the intake boots clamps. Replace if oil soaked/squishy.
Check at the LH that the WOT and idle inputs are working (ground).
No idle contact will make it idle high.
(EZF and LH2.2 pinouts)
What is normal operation for that valve anyway?
Sorry, I forgot to mention that I checked out the WOT/IDLE switch at the LH pinout yesterday. It's working properly. I have that link bookmarked, thanks though!
