Post intake-refesh car is not idling correctly
09-08-2018, 12:27 PM
#1
Instructor
Thread Starter
Post intake-refesh car is not idling correctly
Hi All
Recently had an intake refresh completed on my 1991 S4 (Automatic).
Since picking the car up, I have noticed the start-ups are not quite as crisp, it sometimes idles very low or bounces around a little. It seems to drive and accelerate really nicely on the highway but the concern is in city driving on occasion the idle can go very low at a stop, and it has even stalled at traffic lights a few times- but immediately cranks back up.
Prior to the refresh the car was driving well with NO idling issues.
WHAT WAS REPLACED: Every single hose, gasket, Fuel Injector Seal Kits and knock sensors were replaced by my mechanic. See 928 Specialist List for the complete 87-95 refresh list;
https://www.928gt.com/pc-25785-1403-...for-87-95.aspx
Also at the time of the refresh a rebuilt MAF (from Roger) was installed.
The Idle Stabilizer Valve was NOT replaced.
Also, my radiator and all coolant lines were also replaced at this same time.
Finally I will mention that my car was apart for quite a long time with this refresh and I did have some concerns about things being exposed to humidity/or moisture during that period.
** I realize the list of potential causes of an idling issue is long but what I am hoping to get from you all is what you think the TOP 3 or so most obvious causes would be of this idling issue that I might be able to checkout. Praying the intake doesn’t have to come back off!!
Thanks in advance!
John
Recently had an intake refresh completed on my 1991 S4 (Automatic).
Since picking the car up, I have noticed the start-ups are not quite as crisp, it sometimes idles very low or bounces around a little. It seems to drive and accelerate really nicely on the highway but the concern is in city driving on occasion the idle can go very low at a stop, and it has even stalled at traffic lights a few times- but immediately cranks back up.
Prior to the refresh the car was driving well with NO idling issues.
WHAT WAS REPLACED: Every single hose, gasket, Fuel Injector Seal Kits and knock sensors were replaced by my mechanic. See 928 Specialist List for the complete 87-95 refresh list;
https://www.928gt.com/pc-25785-1403-...for-87-95.aspx
Also at the time of the refresh a rebuilt MAF (from Roger) was installed.
The Idle Stabilizer Valve was NOT replaced.
Also, my radiator and all coolant lines were also replaced at this same time.
Finally I will mention that my car was apart for quite a long time with this refresh and I did have some concerns about things being exposed to humidity/or moisture during that period.
** I realize the list of potential causes of an idling issue is long but what I am hoping to get from you all is what you think the TOP 3 or so most obvious causes would be of this idling issue that I might be able to checkout. Praying the intake doesn’t have to come back off!!
Thanks in advance!
John
09-08-2018, 12:55 PM
#2
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Idle/WOT switch not setup correctly. Or cable issues preventing Idle/WOT switch from operating correctly.
Easy to test with a multimeter. Instructions are in my inspection guide.
Easy to test with a multimeter. Instructions are in my inspection guide.
09-08-2018, 02:18 PM
#3
Instructor
Thread Starter
Hi Dave
Thanks so much for this- I will definitely give it a read.
Somehow I managed to have never seen your guide- at a glance in general it looks fantastic.
John
Thanks so much for this- I will definitely give it a read.
Somehow I managed to have never seen your guide- at a glance in general it looks fantastic.
John
09-08-2018, 06:52 PM
#4
Former Vendor
Whenever things sit around apart for long periods of time, with people unfamiliar with these cars, putting them back together can be problematic.
1. Smoke test for intake leaks.
2. Voltage readings on O2 sensor, when connected.
1. Smoke test for intake leaks.
2. Voltage readings on O2 sensor, when connected.
09-08-2018, 08:14 PM
#6
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09-09-2018, 08:57 PM
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09-10-2018, 10:21 AM
#9
Rennlist Member
If possible, see if you can borrow a known good MAF.
09-11-2018, 09:08 AM
#10
Instructor
Thread Starter
Hi Dave
Just a quick follow up. I have not been able to go through your described testing procedure yet, but wanted to ask.
You mention the possibility that "Idle/WOT switch not setup correctly". Pardon my ignorance on this, but what is an example of how it might it have been incorrectly set up? Thanks
John
Just a quick follow up. I have not been able to go through your described testing procedure yet, but wanted to ask.
You mention the possibility that "Idle/WOT switch not setup correctly". Pardon my ignorance on this, but what is an example of how it might it have been incorrectly set up? Thanks
John
09-11-2018, 12:08 PM
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I’ve also seen idle/wot switches that when set to ‘hair trigger’ would not close the idle circuit when hot and/or with slow pedal return. Testing at both ECU plugs and with-foot-on-pedal is the reliable way to ensure that the proper signal is getting to the ECUs.
If the idle circuit does not close when the throttle plate is closed then all kinds of problems can manifest at low rpms.
09-11-2018, 06:32 PM
#13
Team Owner
quick test is have someone press the pedal a bit while you listen for the click at the throttle quadrant area.
If you dont hear a consistent click then you can loosen the throttle cable adjuster ( this is the cable that goes around the white wheel) a quarter turn at a time.
if no changes after a few turns then the cable adjustment is probably not the issue and the cable can be readjusted to its previous location.
After this then testing via the computer cable pins to verify the signal when the engine is warmed up as Dave has suggested.
If you dont hear a consistent click then you can loosen the throttle cable adjuster ( this is the cable that goes around the white wheel) a quarter turn at a time.
if no changes after a few turns then the cable adjustment is probably not the issue and the cable can be readjusted to its previous location.
After this then testing via the computer cable pins to verify the signal when the engine is warmed up as Dave has suggested.