Idle dipping when clutch pedal is stepped on
09-13-2016, 05:01 PM
#16
Three Wheelin'
You guys, I always jump idle control first before I turn the screw....but now that I think about it, the screw is the screw, so what's the difference if you don't jump idle control? Is it that the computer just compensates if you don't?
09-13-2016, 05:23 PM
#17
Rennlist Member
I think it depends on whether your are adjusting for a target RPM or just turning the screw without a target RPM in mind. If you are setting the base idle to a target speed you have to disable the idle motor because it may react to the changes you cause by diddling with the screw. On the other hand, if you are just making a CCW turn on the screw because you read something on a web forum and are not adjusting base idle for a target, there is no need to disable the idle motor. The screw, as you say, is the screw and neither knows or cares that there is an idle motor.
09-13-2016, 07:48 PM
#18
Burning Brakes
Thread Starter
I have a similar problem on my 86.5 that seems to occur most when the AC is on.
Going through Stan's list, I can attest I have:
1. o2 sensor with less than 2000 miles on it.
2. New ISV.
3. New Temp 2
4. MAF rebuilt in Feb. 2015 with about 1500 miles added on since rebuild.
5. Ignition wires new 3 years ago - gone about 5k miles
6. TPS short harness checked and Idle and WOT switch function verified as OK.
Unless a PO changed it out, my crank sensor was installed when Reagan was President.
I have Porken chips and set my idle and did the CO adjustment using the blink'r procedure.
Watching the tach (if it is actually showing what is going on) shows the idle dropping way down in between 400 and 500 rpm. Sometimes it picks up, sometimes it just dies.
Steve, do you have Porken chips? Also, I have found that the Carquest and Standard Motor Products AC376 IACV's are almost always Bosch units with a sticker over the Bosch part number. These can be found online for $120-$150.
Stan - What is the MAF adjustment procedure?
The only part I could throw at this now would be the CPS. I'd rather not invest the $150 for nothing.
Going through Stan's list, I can attest I have:
1. o2 sensor with less than 2000 miles on it.
2. New ISV.
3. New Temp 2
4. MAF rebuilt in Feb. 2015 with about 1500 miles added on since rebuild.
5. Ignition wires new 3 years ago - gone about 5k miles
6. TPS short harness checked and Idle and WOT switch function verified as OK.
Unless a PO changed it out, my crank sensor was installed when Reagan was President.
I have Porken chips and set my idle and did the CO adjustment using the blink'r procedure.
Watching the tach (if it is actually showing what is going on) shows the idle dropping way down in between 400 and 500 rpm. Sometimes it picks up, sometimes it just dies.
Steve, do you have Porken chips? Also, I have found that the Carquest and Standard Motor Products AC376 IACV's are almost always Bosch units with a sticker over the Bosch part number. These can be found online for $120-$150.
Stan - What is the MAF adjustment procedure?
The only part I could throw at this now would be the CPS. I'd rather not invest the $150 for nothing.
Hopefully this is the real deal, not the same Chinese crap that is on eBay for $49.
Steve
09-13-2016, 08:47 PM
#19
I struggled with this stuff for a while. At first I thought it was the ISV, because it was combined with a high idle. Replaced the ISV, and it seemed to fix the high idle, but now I think the replacement just has slightly less flow due to manufacturing imperfections. Oh well, now I have a spare. The real cause of the high idle was a slight vacuum leak. The ISV didn't fix the stalling when braking hard. That was fixed by a rebuilt MAF. Then like PorKen says, I decided the engine idled a bit smoother with the idle screw open a tiny bit more. Although I suspect this is because I still have a very small vacuum leak. It runs too lean at idle and stumbles a tiny bit if I try to correct for the vacuum leak by tightening the idle screw. It idles smoothly and at the correct speed when my AC is on.
09-13-2016, 08:52 PM
#20
Team Owner
Steve that looks like the Bosch part .
MAF adjustment is disable the idle control to set the idle then adjust the MAF mixture.
to set the mixture you need a gas analyzer OR a porken BLinkR
NOTE if the idle control will not shut off when you jump it at the test port then the computer has been damaged and will need to be replaced as the idle circuit will no longer be controlled .
Otto test the port and see if the idle changes when you jumper the two leads.
If so then , try raising the idle .
also make sure that all of the screw clamps on the hoses are tight,
including the main body to throttle housing, examine the hoses for cracks
inspect the CPS connector for deterioration.
a 944 CPS will also work they are about 65.00 they have a cable thats about 4 inches longer otherwise plug and play
MAF adjustment is disable the idle control to set the idle then adjust the MAF mixture.
to set the mixture you need a gas analyzer OR a porken BLinkR
NOTE if the idle control will not shut off when you jump it at the test port then the computer has been damaged and will need to be replaced as the idle circuit will no longer be controlled .
Otto test the port and see if the idle changes when you jumper the two leads.
If so then , try raising the idle .
also make sure that all of the screw clamps on the hoses are tight,
including the main body to throttle housing, examine the hoses for cracks
inspect the CPS connector for deterioration.
a 944 CPS will also work they are about 65.00 they have a cable thats about 4 inches longer otherwise plug and play
09-13-2016, 09:58 PM
#21
Three Wheelin'
I think it depends on whether your are adjusting for a target RPM or just turning the screw without a target RPM in mind. If you are setting the base idle to a target speed you have to disable the idle motor because it may react to the changes you cause by diddling with the screw. On the other hand, if you are just making a CCW turn on the screw because you read something on a web forum and are not adjusting base idle for a target, there is no need to disable the idle motor. The screw, as you say, is the screw and neither knows or cares that there is an idle motor.
09-13-2016, 10:11 PM
#22
Burning Brakes
Thread Starter
Steve that looks like the Bosch part .
MAF adjustment is disable the idle control to set the idle then adjust the MAF mixture.
to set the mixture you need a gas analyzer OR a porken BLinkR
NOTE if the idle control will not shut off when you jump it at the test port then the computer has been damaged and will need to be replaced as the idle circuit will no longer be controlled .
Otto test the port and see if the idle changes when you jumper the two leads.
If so then , try raising the idle .
also make sure that all of the screw clamps on the hoses are tight,
including the main body to throttle housing, examine the hoses for cracks
inspect the CPS connector for deterioration.
a 944 CPS will also work they are about 65.00 they have a cable thats about 4 inches longer otherwise plug and play
MAF adjustment is disable the idle control to set the idle then adjust the MAF mixture.
to set the mixture you need a gas analyzer OR a porken BLinkR
NOTE if the idle control will not shut off when you jump it at the test port then the computer has been damaged and will need to be replaced as the idle circuit will no longer be controlled .
Otto test the port and see if the idle changes when you jumper the two leads.
If so then , try raising the idle .
also make sure that all of the screw clamps on the hoses are tight,
including the main body to throttle housing, examine the hoses for cracks
inspect the CPS connector for deterioration.
a 944 CPS will also work they are about 65.00 they have a cable thats about 4 inches longer otherwise plug and play
All the ICV out there look like the Bosch unit but are Chinese made stuff so there is no way to tell.
http://www.ebay.com/itm/Fuel-Injecti...FWcSII&vxp=mtr
Steve
09-13-2016, 11:19 PM
#23
Team Owner
I have gotten 4 from FLAPS either advance or autozone and all were Bosch
09-14-2016, 01:19 AM
#24
Rennlist Member
Stan: Thanks for explaining that the blink'r procedure is the MAF adjustment you spoke of. I will follow up on your suggestion of disabling the idle motor and seeing if there is a change.
I don't think I have a vacuum leak and I don't fancy searching for one in the 928 by directing propane at every possible leak point.
Carquest and Standard are both companies with an interest in maintaining the image of their brand as quality aftermarket parts. Standard has been around for as long as I have been buying parts, which I now have to admit is a long time. I think buying either very much increases the chance that you will get the bosch part.
I don't think I have a vacuum leak and I don't fancy searching for one in the 928 by directing propane at every possible leak point.
Carquest and Standard are both companies with an interest in maintaining the image of their brand as quality aftermarket parts. Standard has been around for as long as I have been buying parts, which I now have to admit is a long time. I think buying either very much increases the chance that you will get the bosch part.
09-14-2016, 02:43 AM
#25
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I found my ISV on sale on-line at Napa for way cheaper than $400. There was a thread on it a while back. EDIT: It was the carquest one mentioned above that I bought.
And the only other thing on my car that was weird, is that it would idle really low at first start, but it would run on its own. After the car was warm it would idle a little high it seemed. But it would die just like yours when coming to a stop and then pressing the clutch in, the idle would just drop out and die. It didn't happen every single time. Having the A/C on didn't seem to have an effect one way or another either.
And the only other thing on my car that was weird, is that it would idle really low at first start, but it would run on its own. After the car was warm it would idle a little high it seemed. But it would die just like yours when coming to a stop and then pressing the clutch in, the idle would just drop out and die. It didn't happen every single time. Having the A/C on didn't seem to have an effect one way or another either.
09-14-2016, 01:09 PM
#26
Chronic Tool Dropper
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Since the S3 ISV is relatively easy to change, it may be worth an initial cleaning effort before new replacement. The internals are plastic, and get gummed up by blow-by oil plus crud that gets through the air cleaner. Mostly oil crud and ash though. You can use most common solvents like mineral spirits/paint thinner, but should probably stop well short of brake cleaner, which softens the plastic and eats the insulation from the wires in the motor.
There's also a test procedure that involves looking at the motor disk and a 9V battery to actuate the motor. You'll sometimes be able to see sluggish action caused by stiction.
Also, Blake advises correctly that the TPS (throttle position switch) needs to be carefully considered as you diagnose. Unless the TPS shows that the throttle is at idle position, the ISV is not activated. Additionally, adjusting the throttle stop screw can require a similar adjustment in the TPS position, again making sure that the TPS is correctly indicating closed throttle every time.
There's also a test procedure that involves looking at the motor disk and a 9V battery to actuate the motor. You'll sometimes be able to see sluggish action caused by stiction.
Also, Blake advises correctly that the TPS (throttle position switch) needs to be carefully considered as you diagnose. Unless the TPS shows that the throttle is at idle position, the ISV is not activated. Additionally, adjusting the throttle stop screw can require a similar adjustment in the TPS position, again making sure that the TPS is correctly indicating closed throttle every time.
09-14-2016, 02:02 PM
#27
Rennlist Member
Just a side note on the Idle Air Adjustment screw that should be about a turn open, never completely closed.
Recently I was cleaning an old throttle body and wow the rounded bottom of that screw and the cavity was really dirty (gunked-up).
Don't be afraid to completely remove the screw before making adjustments and clean the rounded bottom and the 'O' ring (on the screw) and spray some brake clean into the hole to loosen up the Gunk.
Then slowly turn the screw in until it seats and back it off one turn, start engine and re-adjust, per procedure
Dave K
Recently I was cleaning an old throttle body and wow the rounded bottom of that screw and the cavity was really dirty (gunked-up).
Don't be afraid to completely remove the screw before making adjustments and clean the rounded bottom and the 'O' ring (on the screw) and spray some brake clean into the hole to loosen up the Gunk.
Then slowly turn the screw in until it seats and back it off one turn, start engine and re-adjust, per procedure
Dave K
09-14-2016, 05:05 PM
#29
Update (sorry to hijack the OP's thread):
I re-seated my MAF a couple of times and re-checked all my vacuum hoses and was able to get the idle speed down, suggesting there was in fact a minor air leak somewhere. One other thing I did was to swap out the "red hat" vacuum plug on the front of the throttle body (CA emissions comlpiant port for the strut bar doohickey/vacuum activated charcoal canister purge control) with a rubber plug, which might fit better.
I boosted the idle to around 750 RPM (only about half a turn out on the idle screw, so I may still have some air coming in somewhere) and it looks like it solved my problem, at least on the drive to work this morning. If it holds up, I will assume the problem was a combination of (1) a small air leak past the MAF with the throttle too far closed to compensate at idle, and (2) the S3 ISV design being inherently a little slow on the uptake when the idle speed dips below the set point.
Thanks to everyone who contributed, and to PorKen for the suggestion to increase the idle a touch. I will probably fiddle with it some and see how low I can set it without running into the same problem.
I hope everyone else with the problem also manages to find a successful resolution. Thanks again! This board is what makes driving a 928 possible (or at least pleasurable).
I re-seated my MAF a couple of times and re-checked all my vacuum hoses and was able to get the idle speed down, suggesting there was in fact a minor air leak somewhere. One other thing I did was to swap out the "red hat" vacuum plug on the front of the throttle body (CA emissions comlpiant port for the strut bar doohickey/vacuum activated charcoal canister purge control) with a rubber plug, which might fit better.
I boosted the idle to around 750 RPM (only about half a turn out on the idle screw, so I may still have some air coming in somewhere) and it looks like it solved my problem, at least on the drive to work this morning. If it holds up, I will assume the problem was a combination of (1) a small air leak past the MAF with the throttle too far closed to compensate at idle, and (2) the S3 ISV design being inherently a little slow on the uptake when the idle speed dips below the set point.
Thanks to everyone who contributed, and to PorKen for the suggestion to increase the idle a touch. I will probably fiddle with it some and see how low I can set it without running into the same problem.
I hope everyone else with the problem also manages to find a successful resolution. Thanks again! This board is what makes driving a 928 possible (or at least pleasurable).
08-10-2021, 11:46 AM
#30
Burning Brakes
Thread Starter
So a little update: I did what Ken advised and it looks to have cured the problem during a short test drive. Thanks to Ken and all the people that have contributed to the discussion.
Steve
Steve
Perhaps because it is too slow to react I found that the S3 idle control needs at least a little bit of bypass air. It does not have to be a perfect 680 RPM. A little higher is often better.
Try turning the throttle body idle screw CCW one turn (open). For sure check that it is not screwed all the way in. At least one full turn open from seated. (If it is closed all the way to get the idle low enough there is probably a vacuum leak somewhere.)
Try turning the throttle body idle screw CCW one turn (open). For sure check that it is not screwed all the way in. At least one full turn open from seated. (If it is closed all the way to get the idle low enough there is probably a vacuum leak somewhere.)