ISV, dirty injectors or something else?
Thread Starter
Drifting
Joined: Dec 2001
Posts: 2,362
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From: Sackville, Nova Scotia
ISV, dirty injectors or something else?
My car (89 S4) has an intermittent problem that seems to indicate a bad Idle Stabilizer Valve.
Symptoms....
1. Car will idle high from time to time (around 1200 rpms)
2. Car will idle low sometimes (550 rpms and voltage gauge drops to 12 or slightly below).
3. When off throttle and moving, it will sometimes "cycle" like gas is cutting out or something. It doesn't ever stall, but you can see the oil pressure flutuate as it's dropping.....moves from say a 3 to a 2.5 and back up again. Once the brake is slightly applied, this "cycle" stops.
After a timing belt change, the tech couldn't get the car to hold and idle for like a day or so. The battery cables were basically sitting on their post (found out later), so perhaps this was a factor. The tech said he believed I had a bad Air Flow Sensor.
Now, here is something I want to touch on that may shed some light. If I shut the car down and leave it for say an hour or two and restart it - not a problem. But, when it sits overnight (or anything over 10 hours), it will stall right away on start-up, if I don't give it gas. The odd time it will stall twice - but usually it starts up fine on the second attempt (all with no touching of the throttle). Seems to me that there is no available gas after it sits for a while.
This leads me to the injectors - I know they are dirty and have run quite a few cleaning bottles through the system (and it's helped slightly). Would really dirty injectors cause this starting problem? It's almost like the gas "seeps" out the injectors over a large time frame and it takes a bit for the gas to get back up through on start-up - does this make sense??
I'm starting to believe I have a bad ISV (because of the high/low idle and looping when off-throttle) AND dirty injectors and his combination is throwing me off.
Bottom line - Would this hard-start after sitting be a better indicator of a bad Idle Valve or dirty injectors?? Or maybe something else?
Thanks,
Jeff
Symptoms....
1. Car will idle high from time to time (around 1200 rpms)
2. Car will idle low sometimes (550 rpms and voltage gauge drops to 12 or slightly below).
3. When off throttle and moving, it will sometimes "cycle" like gas is cutting out or something. It doesn't ever stall, but you can see the oil pressure flutuate as it's dropping.....moves from say a 3 to a 2.5 and back up again. Once the brake is slightly applied, this "cycle" stops.
After a timing belt change, the tech couldn't get the car to hold and idle for like a day or so. The battery cables were basically sitting on their post (found out later), so perhaps this was a factor. The tech said he believed I had a bad Air Flow Sensor.
Now, here is something I want to touch on that may shed some light. If I shut the car down and leave it for say an hour or two and restart it - not a problem. But, when it sits overnight (or anything over 10 hours), it will stall right away on start-up, if I don't give it gas. The odd time it will stall twice - but usually it starts up fine on the second attempt (all with no touching of the throttle). Seems to me that there is no available gas after it sits for a while.
This leads me to the injectors - I know they are dirty and have run quite a few cleaning bottles through the system (and it's helped slightly). Would really dirty injectors cause this starting problem? It's almost like the gas "seeps" out the injectors over a large time frame and it takes a bit for the gas to get back up through on start-up - does this make sense??
I'm starting to believe I have a bad ISV (because of the high/low idle and looping when off-throttle) AND dirty injectors and his combination is throwing me off.
Bottom line - Would this hard-start after sitting be a better indicator of a bad Idle Valve or dirty injectors?? Or maybe something else?
Thanks,
Jeff
Administrator
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From: Up Nort
www.injectors4u.com
I just had all 8 on my car cleaned and flow tested. I mailed them on Thursday (overnight) had them back on Monday.
The ISV can cause all kinds of problems. They are a major bitch on Audi's, mine is bad on my Audi, does a lot of the same things as your car. But it always starts with no problems.
I just had all 8 on my car cleaned and flow tested. I mailed them on Thursday (overnight) had them back on Monday.
The ISV can cause all kinds of problems. They are a major bitch on Audi's, mine is bad on my Audi, does a lot of the same things as your car. But it always starts with no problems.
Three Wheelin'
Joined: Jan 2003
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My vote would be either the MAF or the LH controller going bad.
Have you tried disconnecting the MAF connection to put the car in the
"limp home" mode to see if anything changes? Also you might want to swap the LH with a known good unit to see if that changes anything.
Have you tried disconnecting the MAF connection to put the car in the
"limp home" mode to see if anything changes? Also you might want to swap the LH with a known good unit to see if that changes anything.
Thread Starter
Drifting
Joined: Dec 2001
Posts: 2,362
Likes: 8
From: Sackville, Nova Scotia
I did get the mechanic to disable the MAF sensor to see if it would make the car run better when he was having problems getting it to idle correctly (as per suggestions here), and it ran worse. From what I know, this indicates that the MAF isn't failing.
Three Wheelin'
Joined: Jan 2003
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Sounds like the MAF is passable now. Next would be the LH test in my opinion. When they go bad (if it doesn't fail all at once) they will play havoc and cause all sorts of problems, including all that you are seeing.
I just have a hard time believing that a bad ISV would cause your other drivability problems........most of the time a bad one will just cause a low idle or stalling, same with the injectors........if they are clogged, their clogged and will probably not cause the "cycles" of bad running you are seeing........they would cause poor running all the time.
Other areas to check would be any vacuum leaks, fuel pressure dampers, fuel pressure regulator, etc. You could even have a combination of failures.
Sucks when there's so many places to look.......good luck with it!
I just have a hard time believing that a bad ISV would cause your other drivability problems........most of the time a bad one will just cause a low idle or stalling, same with the injectors........if they are clogged, their clogged and will probably not cause the "cycles" of bad running you are seeing........they would cause poor running all the time.
Other areas to check would be any vacuum leaks, fuel pressure dampers, fuel pressure regulator, etc. You could even have a combination of failures.
Sucks when there's so many places to look.......good luck with it!
Three Wheelin'
Joined: Jan 2003
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Probably the hardest part will be to find someone to who will loan you one to swap. For some details of the swap/replacement check here....
http://members.rennlist.com/v1uhoh/lhbrain.htm
http://members.rennlist.com/v1uhoh/lhbrain.htm
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Thread Starter
Drifting
Joined: Dec 2001
Posts: 2,362
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From: Sackville, Nova Scotia
There is one thing I forgot to mention....
When starting the car after a couple hours...it just starts as normal.
When it sits overnight, as soon as I turn the key, I hear what sounds like a large plastic flap closing...it's quite loud - and it comes from the location of the LH brain. I know there are no moving parts in the LH to make this noise....but it is a coincidence. I wonder what that sound is???
When starting the car after a couple hours...it just starts as normal.
When it sits overnight, as soon as I turn the key, I hear what sounds like a large plastic flap closing...it's quite loud - and it comes from the location of the LH brain. I know there are no moving parts in the LH to make this noise....but it is a coincidence. I wonder what that sound is???
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Rennlist Member
Joined: Feb 2002
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From: Cambridge England
Just to calrify the MAF disconnect test. This is only valid for gross MAF failures, like car will not run at all, or car will not start.
Running in "limp home" is just that. But if the car will start and run - allbeit not very well, then MAF failure has been confirmed.
If the MAF is aged badly, then mainataining a reliable idle becomes more problematic, because of the limited range of the ISV system, and also the O2 loop. Disconnecting the MAF will not prove much at all.
The MAF can only age by 4% before there will be problems with the ISV system and O2 loop. On non cat cars, thelimit is 2%.
Hope this clarifies things.
Running in "limp home" is just that. But if the car will start and run - allbeit not very well, then MAF failure has been confirmed.
If the MAF is aged badly, then mainataining a reliable idle becomes more problematic, because of the limited range of the ISV system, and also the O2 loop. Disconnecting the MAF will not prove much at all.
The MAF can only age by 4% before there will be problems with the ISV system and O2 loop. On non cat cars, thelimit is 2%.
Hope this clarifies things.
Three Wheelin'
Joined: Jan 2003
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Originally posted by 944S Boyeee
There is one thing I forgot to mention....
When starting the car after a couple hours...it just starts as normal.
When it sits overnight, as soon as I turn the key, I hear what sounds like a large plastic flap closing...it's quite loud - and it comes from the location of the LH brain. I know there are no moving parts in the LH to make this noise....but it is a coincidence. I wonder what that sound is???
There is one thing I forgot to mention....
When starting the car after a couple hours...it just starts as normal.
When it sits overnight, as soon as I turn the key, I hear what sounds like a large plastic flap closing...it's quite loud - and it comes from the location of the LH brain. I know there are no moving parts in the LH to make this noise....but it is a coincidence. I wonder what that sound is???
Thread Starter
Drifting
Joined: Dec 2001
Posts: 2,362
Likes: 8
From: Sackville, Nova Scotia
Originally posted by MikeN
Its the climate control recirculation flap.......right above the fuse/relay panel. If you look above the panel you will see a plastic grate with a larger opening in the middle. You should be able to look or put a finger in the opening and touch the flap. After it sits overnight or longer, vacuum slowly leaks out of the A/C vent system and the flap lowers and "sticks" to the seal above the grate. When you start the car, the vacuum returns in the system and the flap vacuum pot pulls the flap up with a loud "unsticking" sound.........normal.
Its the climate control recirculation flap.......right above the fuse/relay panel. If you look above the panel you will see a plastic grate with a larger opening in the middle. You should be able to look or put a finger in the opening and touch the flap. After it sits overnight or longer, vacuum slowly leaks out of the A/C vent system and the flap lowers and "sticks" to the seal above the grate. When you start the car, the vacuum returns in the system and the flap vacuum pot pulls the flap up with a loud "unsticking" sound.........normal.
Seeing as we are playing "name that sound", here is another one.
After putting the car in park, once in like every 25 times, I will hear a "moan" coming from what appears to be where the coolant reservoir tanks sits. This moan will remain until I blip the throttle, then it goes away. Almost like a sticking/wearing alternator or something. Any guesses??
Jeff
Three Wheelin'
Joined: Jan 2003
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Originally posted by 944S Boyeee
Sweet - another sound that will no longer haunt me in my dreams! Thanks so much.
Seeing as we are playing "name that sound", here is another one.
After putting the car in park, once in like every 25 times, I will hear a "moan" coming from what appears to be where the coolant reservoir tanks sits. This moan will remain until I blip the throttle, then it goes away. Almost like a sticking/wearing alternator or something. Any guesses??
Jeff
Sweet - another sound that will no longer haunt me in my dreams! Thanks so much.
Seeing as we are playing "name that sound", here is another one.
After putting the car in park, once in like every 25 times, I will hear a "moan" coming from what appears to be where the coolant reservoir tanks sits. This moan will remain until I blip the throttle, then it goes away. Almost like a sticking/wearing alternator or something. Any guesses??
Jeff
http://members.rennlist.com/v1uhoh/underthe.htm
Rennlist Member
Joined: Oct 2003
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From: Nova Scotia
Jeff,
When you had your car here, I did get to spray some lube into the ICV line (Check Tony's site to locate the correct line), but never stayed with it because of the point below. That's a good thing to redo - search under idle control valve also. This still may be part of the variation of idle issue
The issue that side tracked me was the look for obvious vacuum leaks - and we found a wopper!. The "Y" connector near the throttle cable quadrant that is in the vac line to the brake booster - that is the one that seperated in my hand! It looks like an orfice tube inserted in the "Y", but it was flopping around. The white teflon tape I wrapped on the taper and jammed together is only a temp. fix.
BTW, other than replacement, what is the better repair to seal it - RTV silicon? - plastic pipe cement?
These two may correct some of the idle issues.
I agree w. Mike re the HVAC system flap in the passenger footwell - link this to the obvious vacuum leak above: system vac dissapears too quickly.
When you had your car here, I did get to spray some lube into the ICV line (Check Tony's site to locate the correct line), but never stayed with it because of the point below. That's a good thing to redo - search under idle control valve also. This still may be part of the variation of idle issue
The issue that side tracked me was the look for obvious vacuum leaks - and we found a wopper!. The "Y" connector near the throttle cable quadrant that is in the vac line to the brake booster - that is the one that seperated in my hand! It looks like an orfice tube inserted in the "Y", but it was flopping around. The white teflon tape I wrapped on the taper and jammed together is only a temp. fix.
BTW, other than replacement, what is the better repair to seal it - RTV silicon? - plastic pipe cement?
These two may correct some of the idle issues.
I agree w. Mike re the HVAC system flap in the passenger footwell - link this to the obvious vacuum leak above: system vac dissapears too quickly.
Thread Starter
Drifting
Joined: Dec 2001
Posts: 2,362
Likes: 8
From: Sackville, Nova Scotia
Thanks Garth and Mike......
Garth, I forgot all about that Y-fitting piece!! I will say one thing, ever since you spayed that lub into that fitting - the high idle problem has lessened by at least 70-80%.....I get a proper idle a lot more now. My idle isn't too shabby - but that looping when off throttle is annoying.
I will order a new "Venturi Y-fitting" to put in that spot where that loose connection was and see if that helps. Any guesses on that part number anyone?
Also, Garth said that HVAC flap opening is an indication of poor vacuum....would this "leaking" of vacuum cause my problem with the car not starting on the first try after it sits for a extended time? Would the lack of vacuum effect start-up? I'm guessing it would.
Jeff
Garth, I forgot all about that Y-fitting piece!! I will say one thing, ever since you spayed that lub into that fitting - the high idle problem has lessened by at least 70-80%.....I get a proper idle a lot more now. My idle isn't too shabby - but that looping when off throttle is annoying.
I will order a new "Venturi Y-fitting" to put in that spot where that loose connection was and see if that helps. Any guesses on that part number anyone?
Also, Garth said that HVAC flap opening is an indication of poor vacuum....would this "leaking" of vacuum cause my problem with the car not starting on the first try after it sits for a extended time? Would the lack of vacuum effect start-up? I'm guessing it would.
Jeff
Three Wheelin'
Joined: Jan 2003
Posts: 1,447
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Originally posted by 944S Boyeee
Thanks Garth and Mike......
Also, Garth said that HVAC flap opening is an indication of poor vacuum....would this "leaking" of vacuum cause my problem with the car not starting on the first try after it sits for a extended time? Would the lack of vacuum effect start-up? I'm guessing it would.
Jeff
Thanks Garth and Mike......
Also, Garth said that HVAC flap opening is an indication of poor vacuum....would this "leaking" of vacuum cause my problem with the car not starting on the first try after it sits for a extended time? Would the lack of vacuum effect start-up? I'm guessing it would.
Jeff
You might still have some vacuum problems on the engine side that could be causing or making some of your running problems worse though.
