High Idle-only after warm-up
09-25-2017, 10:42 AM
#1
Racer
Thread Starter
High Idle-only after warm-up
91 S4-Last thing I did that attributed to this is I removed intake and water-bridge to install Greg Brown's oil baffle, new oil filler neck(with DreiBond), new intake gaskets, and a new TPS since that was the only item I did not replace when I did the intake refresh a year ago.
What happens is it idles at 675 until it gets to operating temp and then rises from 800 to 900 rpm. I can shut it off and start it right back and it idles at 675 for about 2 minutes but then it seems something else takes over and up to 800 to 900 again.
TIA- I am sure one of you gurus know how the idle loop functions and may be able to shed light on this for me.
Also, Temp II is 6 months old and I checked resistance and is within spec and MAF is 6 month old from Roger.
What happens is it idles at 675 until it gets to operating temp and then rises from 800 to 900 rpm. I can shut it off and start it right back and it idles at 675 for about 2 minutes but then it seems something else takes over and up to 800 to 900 again.
TIA- I am sure one of you gurus know how the idle loop functions and may be able to shed light on this for me.
Also, Temp II is 6 months old and I checked resistance and is within spec and MAF is 6 month old from Roger.
Last edited by Taguid; 11-06-2017 at 09:30 AM.
09-25-2017, 12:42 PM
#4
Addict
Rennlist Member
Rennlist Member
Join Date: Oct 2003
Location: Gone. On the Open Road
Posts: 16,329
Received 1,543 Likes
on
1,007 Posts
Your idle is going unstable once the O2 sensor is warmed and the LH switches to closed-loop idle control.
Occam's Razor: you didn't get everything just right on the intake R&R. And you put in a new "TPS" which leads to:
You didn't get the set-up of the idle switch on your new "TPS" correct.
Test your idle switch operation at the ECU pins (directions in my inspection guide.) If you have a Bosch Hammer or Theo Tool, then use that instead.
Occam's Razor: you didn't get everything just right on the intake R&R. And you put in a new "TPS" which leads to:
You didn't get the set-up of the idle switch on your new "TPS" correct.
Test your idle switch operation at the ECU pins (directions in my inspection guide.) If you have a Bosch Hammer or Theo Tool, then use that instead.
09-25-2017, 02:49 PM
#5
Racer
Thread Starter
Your idle is going unstable once the O2 sensor is warmed and the LH switches to closed-loop idle control.
Occam's Razor: you didn't get everything just right on the intake R&R. And you put in a new "TPS" which leads to:
You didn't get the set-up of the idle switch on your new "TPS" correct.
Test your idle switch operation at the ECU pins (directions in my inspection guide.) If you have a Bosch Hammer or Theo Tool, then use that instead.
Occam's Razor: you didn't get everything just right on the intake R&R. And you put in a new "TPS" which leads to:
You didn't get the set-up of the idle switch on your new "TPS" correct.
Test your idle switch operation at the ECU pins (directions in my inspection guide.) If you have a Bosch Hammer or Theo Tool, then use that instead.
09-25-2017, 04:05 PM
#6
Addict
Rennlist Member
Rennlist Member
Join Date: Oct 2003
Location: Gone. On the Open Road
Posts: 16,329
Received 1,543 Likes
on
1,007 Posts
First, let's clear up something: Warm idle for an S4 should be 650-700. Starting from shop-cold it should idle 100-200 rpm higher and over the course of roughly a minute drop steadily to the warm range. Then, after about another minute or two, when the LH decides that the o2 sensor has had enough time to warm up, the LH will begin attempting to stabilize idle via the ISV/ICV using the o2 sensor, rpm signal and mass-air sensor as inputs to the control law.
So, there are three phases from a cold start. Paying attention to the idle during these phases may help point you in the right direction.
While you're there with the meter out and the ECUs disconnected, go ahead and test both circuits of the TEMP-II and test the ISV/ICV for function.
Also, make sure that you hear the idle click on throttle return under all circumstances. I've had a couple of idle/wot (TPS) switches where the idle contact - when set to hair-trigger - would not close on a gentle return of the throttle.
Those three checks (idle, temp-II, ISV/ICV) should rule-in/-out some obvious causes.
Occam's Razor suggests that if the problem started right after your intake R&R that the problem was caused by something done (or not done) during the work.
Next, is your water bridge coated? Painted?
So, there are three phases from a cold start. Paying attention to the idle during these phases may help point you in the right direction.
Also, make sure that you hear the idle click on throttle return under all circumstances. I've had a couple of idle/wot (TPS) switches where the idle contact - when set to hair-trigger - would not close on a gentle return of the throttle.
Those three checks (idle, temp-II, ISV/ICV) should rule-in/-out some obvious causes.
Occam's Razor suggests that if the problem started right after your intake R&R that the problem was caused by something done (or not done) during the work.
Next, is your water bridge coated? Painted?
09-25-2017, 04:35 PM
#7
Racer
Thread Starter
^^^ From shop cold it does not happen until it is approx 83C but within 2 minutes after restarting when warm.
It did not start after the intake R&R. That was a year ago. It has started a few days ago when I removed the intake to install GB's baffle. I just changed the TPS because it was the only thing I had not replaced a year ago so I figured since I was in there I would replace it. It does not have the hair-trigger I made sure of that.
The water-bridge is bare not powder coated or painted. I hear the clicking working just as it should. I will do the 3 checks just rule them out.
It did not start after the intake R&R. That was a year ago. It has started a few days ago when I removed the intake to install GB's baffle. I just changed the TPS because it was the only thing I had not replaced a year ago so I figured since I was in there I would replace it. It does not have the hair-trigger I made sure of that.
The water-bridge is bare not powder coated or painted. I hear the clicking working just as it should. I will do the 3 checks just rule them out.
Trending Topics
09-26-2017, 09:33 AM
#8
Racer
Thread Starter
I was able to perform a TPS idle and WOT on the LH and seem to function fine. I have an auto-ranging meter so I did not get OL because it switched to kilo-ohms. See links to video
https://www.dropbox.com/s/3n98wcbeh1...-test.MOV?dl=0
https://www.dropbox.com/s/o1afln2fsz..._test.MOV?dl=0
I also tested Temp II at LH and at 83F it was 1.75K ohms which is within range.
I will continue the testing but I have not found anything yet.
https://www.dropbox.com/s/3n98wcbeh1...-test.MOV?dl=0
https://www.dropbox.com/s/o1afln2fsz..._test.MOV?dl=0
I also tested Temp II at LH and at 83F it was 1.75K ohms which is within range.
I will continue the testing but I have not found anything yet.
10-17-2017, 03:29 PM
#10
Racer
Thread Starter
I performed an intake leak test following Dwayne's write-up along with a smoke leak detector and found a vacuum leak at the vacuum valve 928.110.429.08-- The diaphragm is blown out. After plugging and checking again it held the 2.5 psi pretty well but my oil filler cap is leaking a bit so I have both on the way to replace.
I am going to remove intake again and readjust the TPS because the I have it adjusted too far in because WOT only trips when held on the floor pushing really hard. I wanted to make sure the idle switch worked but adjusted too far for WOT.
If that doesn't work I will use a Bosch Hammer or Theo J's system to troubleshoot further. I'll keep you up on my progress.
I am going to remove intake again and readjust the TPS because the I have it adjusted too far in because WOT only trips when held on the floor pushing really hard. I wanted to make sure the idle switch worked but adjusted too far for WOT.
If that doesn't work I will use a Bosch Hammer or Theo J's system to troubleshoot further. I'll keep you up on my progress.
10-17-2017, 05:19 PM
#11
Rennlist Member
I performed an intake leak test following Dwayne's write-up along with a smoke leak detector and found a vacuum leak at the vacuum valve 928.110.429.08-- The diaphragm is blown out. After plugging and checking again it held the 2.5 psi pretty well but my oil filler cap is leaking a bit so I have both on the way to replace.
I am going to remove intake again and readjust the TPS because the I have it adjusted too far in because WOT only trips when held on the floor pushing really hard. I wanted to make sure the idle switch worked but adjusted too far for WOT.
If that doesn't work I will use a Bosch Hammer or Theo J's system to troubleshoot further. I'll keep you up on my progress.
I am going to remove intake again and readjust the TPS because the I have it adjusted too far in because WOT only trips when held on the floor pushing really hard. I wanted to make sure the idle switch worked but adjusted too far for WOT.
If that doesn't work I will use a Bosch Hammer or Theo J's system to troubleshoot further. I'll keep you up on my progress.
10-18-2017, 09:17 AM
#12
Racer
Thread Starter
10-18-2017, 10:30 AM
#13
Team Owner
FWIW WOT should be triggered near or after 75% of throttle opening.
The only adjustment you make on the TPS is setting the idle closed contacts.
You might also be missing the fact that the TPS unit could be set properly BUT,
the throttle cable could be set too tight thus when the intake gets hot the parts expand and the cable becomes too tight.
Instead of taking off the intake lets say you got it right the first time.
Try unscrewing the tension of the cable housing for the throttle cable the one that goes around the wheel.
Remove one turn of tension then drive the car, you wouldn't be the first to have this cable too tight
NOTE make sure the wheel is free to turn they can get sticky and prevent the cable free movement
The only adjustment you make on the TPS is setting the idle closed contacts.
You might also be missing the fact that the TPS unit could be set properly BUT,
the throttle cable could be set too tight thus when the intake gets hot the parts expand and the cable becomes too tight.
Instead of taking off the intake lets say you got it right the first time.
Try unscrewing the tension of the cable housing for the throttle cable the one that goes around the wheel.
Remove one turn of tension then drive the car, you wouldn't be the first to have this cable too tight
NOTE make sure the wheel is free to turn they can get sticky and prevent the cable free movement
Last edited by Mrmerlin; 10-18-2017 at 10:46 AM.
10-18-2017, 10:57 AM
#14
Racer
Thread Starter
FWIW WOT should be triggered near or after 75% of throttle opening.
The only adjustment you make on the TPS is setting the idle closed contacts.
You might also be missing the fact that the TPS unit could be set properly BUT,
the throttle cable could be set too tight thus when the intake gets hot the parts expand and the cable becomes too tight.
Instead of taking off the intake lets say you got it right the first time.
Try unscrewing the tension of the cable housing for the throttle cable the one that goes around the wheel.
Remove one turn of tension then drive the car, you wouldnt be the fiorst to have this cable too tight
NOTE make sure the wheel is free to turn they can get sticky and prevent the cable free movement
The only adjustment you make on the TPS is setting the idle closed contacts.
You might also be missing the fact that the TPS unit could be set properly BUT,
the throttle cable could be set too tight thus when the intake gets hot the parts expand and the cable becomes too tight.
Instead of taking off the intake lets say you got it right the first time.
Try unscrewing the tension of the cable housing for the throttle cable the one that goes around the wheel.
Remove one turn of tension then drive the car, you wouldnt be the fiorst to have this cable too tight
NOTE make sure the wheel is free to turn they can get sticky and prevent the cable free movement
10-22-2017, 03:34 PM
#15
Racer
Thread Starter
I knew I had over-adjusted the TPS because I knew I had set it as far as it would go toward the MAF to make sure it would click at idle. I went back in and readjusted the TPS to about what it was originally and Voila it idles near the 675 as it should without the 200 rpm kick-up. So problem solved.
I really wouldn't have believed this would have fixed it but apparently the over adjustment was sending something to the ECU when it went to closed loop that kicked it up the extra 200 rpm. That's my story unless someone else has better explanation of what might have happened.
I really wouldn't have believed this would have fixed it but apparently the over adjustment was sending something to the ECU when it went to closed loop that kicked it up the extra 200 rpm. That's my story unless someone else has better explanation of what might have happened.