Its making me crazy, I have gone thru all my vacum lines and they all appear to be good, I have tried multiple o2 sensors. I have adjusted my idle screw, with no serious improvements. running out of ideas here any one have any fresh suggestions.
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Lonewolf64
Well-known member
Two things you should do. Check that your TPS is properly working and make sure it is set correctly with a palm datalogger or ohm-meter as per vfaq instructions. As soon as this is done, set your idle per the vfaq instructions (you have two ground out two pins before messing with BISS screw to set the idle correctly and reset the ISC correction).
GVR4_1057
Well-known member
I replaced my ISC with one of the later model black ones and it fixed my problem.
dmj
Well-known member
check the isc and also your computer . if your ecm has not been rebuilt the isc circuit could be burnt out.pm Keydiver
Ok so I cleaned the TB, FIAV looks good, but i was unable to find a way to test it. I tested the ISC, it was bad, replaced it. Oh I also adjusted the BISS (per vfaq instructions). My situation has improved, the car will idle fine at start up, and will do so just until it is fully warmed up. I have installed DSM LINk but that is all.
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toybreaker
iconoclast
- Joined
- Apr 30, 2006
- Messages
- 3,581
Is the throttle body ground tab under the top front mounting bolt?
If you've removed the brace, or the tab is mia, the closed throttle switch on the t-body won't be grounded strongly/consistently enough for the system to work as intended when the motor's warm.
You can just run a ground wire from under the screw head up on top of the t-body over to the firewall (or intake mani), and that should finish the job.
If you've removed the brace, or the tab is mia, the closed throttle switch on the t-body won't be grounded strongly/consistently enough for the system to work as intended when the motor's warm.
You can just run a ground wire from under the screw head up on top of the t-body over to the firewall (or intake mani), and that should finish the job.
s_firestone
Well-known member
You likely still have too much air passing through. Is this a slow steady up/down even surge or a fast (once every 1 to 2 seconds) surge that ramps steadily up to an RPM threshold then drops quickly and repeats.
If the BISS is opened beyond a threshold that the ISC can control, then the idle will start oscillating. The ECU sees that the idle is too high and probably attempts to reset the idle by cutting fuel. It will ramp up until it hits about 1500~1800 RPM then drop rapidly to about 800 then repeat over and over.
I know from experience that this can happen from adjusting the BISS when the engine is not in Idle set mode. It will also happen if you have too much air bypassing the butterfly. The FIAV usually goes bad and amplifies this problem by allowing way too much air through all the time(its supposed to actuate a plunger as it warms up and the wax melts. A bad BISS O-ring will also cause this problem. As will a vacuum hose leak past the butterfly. An incorrectly adjusted CTPS butterfly clearance as well.
Turn the BISS inward a half turn at a time (with a few seconds in between) until the surge stops.
If the BISS is operating correctly the idle will go down until the engine stalls. If the engine will not stall there is too much air bypassing the TB butterfly.
If the surge stops as you turn the BISS down then you've gotten under the threshold that the ISC (assuming its fully functioning) can control. The RPM at this point will likely tell you how much the leak deviates from what the design is. Remember stock idle is 850 I think. (I don't think my car ever idled that low, it idled at 1050 RPM when I bought it.)
The bigger the leak the less impact(change in RPM) the ISC will have across it's full range of motion. This can be to the point that the ECU cannot drop the idle low enough that it feels it must reset the idle. The ECU is simply following a list of instructions of what should happen during idle and in this case endlessly repeats the same steps.
The short list of most common problems are as follows:
Bad seal or incorrectly adjusted BISS
Bad FIAV
-requires blocking off FIAV
Bad ISC
-Test, replace. A bad ISC can destroy the ECU facilitating repair and vice versa.
Bad ECU (incapable of actuating the ISC until repaired)
-Odds are that if your ISC was bad, then this may be the culprit, and the ECU can/will kill a new ISC and vice versa.
This will require some more troubleshooting on your part. Break it down into smaller, easier to solve problems. Think in terms of what you do know about the problem.
And read the Idle Surge FAQ on the VFAQ/Intake Section
If anything I've written is incorrect, please feel free to correct me.
If the BISS is opened beyond a threshold that the ISC can control, then the idle will start oscillating. The ECU sees that the idle is too high and probably attempts to reset the idle by cutting fuel. It will ramp up until it hits about 1500~1800 RPM then drop rapidly to about 800 then repeat over and over.
I know from experience that this can happen from adjusting the BISS when the engine is not in Idle set mode. It will also happen if you have too much air bypassing the butterfly. The FIAV usually goes bad and amplifies this problem by allowing way too much air through all the time(its supposed to actuate a plunger as it warms up and the wax melts. A bad BISS O-ring will also cause this problem. As will a vacuum hose leak past the butterfly. An incorrectly adjusted CTPS butterfly clearance as well.
Turn the BISS inward a half turn at a time (with a few seconds in between) until the surge stops.
If the BISS is operating correctly the idle will go down until the engine stalls. If the engine will not stall there is too much air bypassing the TB butterfly.
If the surge stops as you turn the BISS down then you've gotten under the threshold that the ISC (assuming its fully functioning) can control. The RPM at this point will likely tell you how much the leak deviates from what the design is. Remember stock idle is 850 I think. (I don't think my car ever idled that low, it idled at 1050 RPM when I bought it.)
The bigger the leak the less impact(change in RPM) the ISC will have across it's full range of motion. This can be to the point that the ECU cannot drop the idle low enough that it feels it must reset the idle. The ECU is simply following a list of instructions of what should happen during idle and in this case endlessly repeats the same steps.
The short list of most common problems are as follows:
Bad seal or incorrectly adjusted BISS
Bad FIAV
-requires blocking off FIAV
Bad ISC
-Test, replace. A bad ISC can destroy the ECU facilitating repair and vice versa.
Bad ECU (incapable of actuating the ISC until repaired)
-Odds are that if your ISC was bad, then this may be the culprit, and the ECU can/will kill a new ISC and vice versa.
This will require some more troubleshooting on your part. Break it down into smaller, easier to solve problems. Think in terms of what you do know about the problem.
And read the Idle Surge FAQ on the VFAQ/Intake Section
If anything I've written is incorrect, please feel free to correct me.
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I grounded out the trottle body and managed to bring the idle down to 900 hundred. But this is only when I stop, if Im rolling it will still surge.
s_firestone
Well-known member
Do you have your ABS disabled?
Are you sure the idle-closed switch on the throttlebody is working? If the ECU isn't seeing the switch grounding that wire it will not know the throttle is closed, and it will surge.
Also, as Steve asked, if the ABS isn't disabled correctly you will get an idle surge whenever the car is moving >12 mph.
Also, as Steve asked, if the ABS isn't disabled correctly you will get an idle surge whenever the car is moving >12 mph.
I've found the Thermo Valve in the Throttle Body is also one of the problems.. along with the replacement of my IAC it took care of mine..
Quoting keydiver:
Are you sure the idle-closed switch on the throttlebody is working? If the ECU isn't seeing the switch grounding that wire it will not know the throttle is closed, and it will surge.
Also, as Steve asked, if the ABS isn't disabled correctly you will get an idle surge whenever the car is moving >12 mph.
What do you have to do to correctly remove ABS? The car I bought has it removed.
Are you sure the idle-closed switch on the throttlebody is working? If the ECU isn't seeing the switch grounding that wire it will not know the throttle is closed, and it will surge.
Also, as Steve asked, if the ABS isn't disabled correctly you will get an idle surge whenever the car is moving >12 mph.
What do you have to do to correctly remove ABS? The car I bought has it removed.
3rdstrikedsm
Well-known member
I am also wondering about this.
SmoothCustomer
Well-known member
I think you need to find a 1g non abs shell and swap all of the components that aren't abs related into the gvr4 (as far as just brake stuff)
3rdstrikedsm
Well-known member
Yea, I am talking about the eletronic part of it.
If you just cut the wire to pin #11 of the ECU, the ECU will no longer be looking at the ABS signal, so you will never have any issue with the idle raising because the ECU thinks the ABS is activated.
ECU Pinout
ECU Pinout
