what controls Idle

[mattspyder]

What controls the Idle so when I rev it up at Idle and then let off the pedal it doesn't die. I changed out the TPS, made sure it was good use the how to guide on here and I still get idle drop. I can get it to idle good just sitting but when I rev it up high it will almost die. What causes this? I made sure everything was tight so I doubt it's a boost leak

 

[ilco187]

biss and fiav i really dont know 2g's that much but those are my guess.

are you venting the bov that will cause it to stall after revving.

 

[gusu]

Failed EGR can cause it. Needing to clean your throttle body will also cause it.

I'd block off the EGR since it costs about 15 bucks. You can find the gaskets and block off plates online very cheap. To cap it off is very easy and VFAQ has a tutorial on how to do it.

It could also be that your ECU has bad caps because of the bad TPS. When the TPS fails it causes a strain on the ECU and will eventually cause the caps to leak. If you had your caps replaced by a nonprofessional they were almost defiantly done wrong no matter how well you think the person can solder.

 

[Jeff99GS]

The ISC (idle speed control) it's just underneath the throttle body. Mine went bad about a year ago.

 

[mattspyder]

Failed EGR can cause it. Needing to clean your throttle body will also cause it.

I'd block off the EGR since it costs about 15 bucks. You can find the gaskets and block off plates online very cheap. To cap it off is very easy and VFAQ has a tutorial on how to do it.

It could also be that your ECU has bad caps because of the bad TPS. When the TPS fails it causes a strain on the ECU and will eventually cause the caps to leak. If you had your caps replaced by a nonprofessional they were almost defiantly done wrong no matter how well you think the person can solder.

2Gs have the EGR on the firewall, and then I have the other part capped off

anyone else?

 

[Elek_ron_ix]

The ISC (idle speed control) it's just underneath the throttle body. Mine went bad about a year ago.

I agree, My ISC went bad due to a bad a year ago and had to replace. The gasket sometimes around it also goes bad also. During a leakdown test I found mine to be leaking. So definitely would be a good starting place to look. My Idle was perfect after figuring that out.

 

[ulitka]

Are you able to capture TPS voltage (it should be 0.63V @idle)?
Are you able to capture ISC position at idle with engine fully warmed up (it shold be around 30)?
Are you able to capture ISC "learned postion" (it shold be around 140)?

Did you test your ISC coils resistence using a voltmeter?

 

[dyetrying91]

Agreed with above poster. Check your ISC. Take it off but leave it plugged in, turn the car to on, BUT DON'T START IT. You should hear the ISC click rather loudly, then turn the car off, and it should click again. If it doesn't click, replace.

 

[steve]

It could also be that your ECU has bad caps because of the bad TPS. When the TPS fails it causes a strain on the ECU and will eventually cause the caps to leak.

Nope, the TPS isn't going to stress the capacitors, if it's bad (shorted) it burns up the current limiting resistor on the 5v sensor power feed.

The caps go bad because the seal around the wires leaks. It seems to be more a temp and age related problem with a couple of specific capacitors. They leak in all the parts they were used in.

The ISC (idle speed control) it's just underneath the throttle body. Mine went bad about a year ago.

We have a winner

Are you able to capture TPS voltage (it should be 0.63V @idle)?

Did you test your ISC coils resistence using a voltmeter?

Only DSMLink wants 0.63v at idle and on a 2G it's the IPS switching point that's really important, if you get that right the voltage won't be far off. On a stock 2G ECU the IPS switching point is the critical TPS adjustment.

Measuring the ISC resistance of the 4 coils in the ISC is an important test both to see if it's bad and to know if it damaged the driver in the ECU.

Agreed with above poster. Check your ISC. Take it off but leave it plugged in, turn the car to on, BUT DON'T START IT. You should hear the ISC click rather loudly, then turn the car off, and it should click again. If it doesn't click, replace.

This is what it should do.

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[mattspyder]

I just went out and tested the ISC with the ohm reader and also turning the key on and watching it click and move, both came out fine.

So that pretty much removes the ISC from the problem, what could it be now?

 

[steve]

Make sure that the TPS is correctly adjusted as required for a 2G (by setting the IPS switching point, clean the throttle body and set your base idle speed adjustment. (BISS)

 

[mattspyder]

I adjusted the the TPS yesterday following your steps. I ran seafoam through it last night, I'm in the car right now with my evo scan hooked up and its currently idleing at 781-812

it only wants to die down after I rev it up 6k or I bounce the throttle around from around 3-4-5

On my evo scan it's reading that my Throttle position at Idle is 14.9% I thought I read someone that it needs to be 11.9%??? is that correct?

 

[steve]

On a 2G it's the IPS switching point that is important. The TPS will read whatever it does and that's find as long as the IPS switches off as soon as the throttle opens.

On a 1G the TPS should read 10% because it's not directly coupled to the IPS.

I think your problem is due to the lightweight flywheel. You'll have to reflash the ECU to raise the point where the injectors kick back on during decel when the IPS is closed to fix it.

 

[ulitka]

Did this issue start happening after you changed something? Do you have a recirculated BOV setup? Did you hack your MAF? What kind of intake pipe do you have?

I had some fun today adjusting my idle after installation of bunch of parts like boomba throttle body, arc2 dis, smim, huge fmic setup, tial q bov. Car would not idle at all, after few attempts to crank the engine I ended up flooding cylinders with gas and messing up my spark plugs. In order yo make car idle I had to open TB plate using an adjustment screw and calibrate TPS to read 0.63V. Once I took car for a test drive I began having the same issue you have. I pulled spark plugs out and sure enough they looked like crap after I flooded them, so, I replaced plugs with a new set and no more issues.
If I was you, I would check condition of your spark plugs, measure voltage from TPS with ignition key in on position but engine not running to insure you get 0.63V, next i would play with BISS by opening it up counter clock wise in 1/4 intervals and driving car in between to see if it makes any difference. You can also try adjusting the throttle plate with an adjustment screw but it would require re-calibration of TPS after each adjustment.

 

[mattspyder]

I never thought about that, the flywheel causing idle issues. Interesting.
I actually just changed my plugs couple weeks ago. I'm running a stock rubber intake pipe with K&N cone filter. Running stock boost on a 14b turbo. 2100 clutch kit with lightened flywheel. (its not the super lightweight flywheel)
I wouldn't mind adjust the TPS but its just a pain in the ass getting to the bottom bolt. I don't think I adjusted it with the ingnition on. I just left it on the flywheel and turned it until there was no readong on the ohm meter (this was for the pins 3 and 4)

 

[ulitka]

When did you start having this issue? Did this issue occure after you replaced or upgraded part(s)? Try opening up throttle plate in small increments with an adjustment TB screw.

 

[steve]

Please don't touch the fixed SAS. The factory cautions against ever adjusting it. Your just as likely to induce a bad case of idle surge as you are to fix this issue.

 

[ulitka]

Please don't touch the fixed SAS. The factory cautions against ever adjusting it. Your just as likely to induce a bad case of idle surge as you are to fix this issue.

I agree with you. Manufacture precisely adjusted SAS when the car was new. After many years of service and some upgrades like a light weight flywheel may require some adjustments here and there. The good thing is that there is a backout plan as documented in a service manual plus SAS screw could be marked before doing any adjustments. I did not have any sick affects when I adjusted SAS on my 2G TB, had to do it because FIAV was blocked and upgrade to Kelford 280s cams caused cold idle issues.

From service manual:
FIXED SAS ADJUSTMENT NOTE
1. The fixed SAS should not be moved unnecessarily;
it has been precisely adjusted by the manufacturer.
2 . If the adjustment is disturbed for any reason, readjust
as follows.
1. Loosen the tension of the accelerator cable sufficiently.
2. Back out the fixed SAS lock nut.
3. Turn the fixed SAS counterclockwise until it is sufficiently
backed out, and fully close the throttle valve.
4. Turn the fixed SAS clockwise until the throttle lever is
touched (i.e., the point at which the throttle valve begins
to open).
From that point, turn the fixed SAS clockwise another
1-1/4 turn .
5. While holding the fixed SAS so that it doesn’t move, tighten
the lock nut securely.
6. Adjust the tension of the accelerator cable.
7. Adjust the basic idle speed.
8. Adjust the closed throttle position switch and the throttle
position sensor.

 

[rimmbrme]

ALLDATA TEST FOR ISC:






Verify that the Idle Speed Control Servo stepper motor is operating by listening for sound when the ignition switch is turned to the ON position (without cranking the engine).
If the Idle Speed Control Servo does not make an audible sound, the possible cause may be the stepper motor actuation circuit, electrical connections, the Control Module, or the stepper motor itself.
Checking The ISC Servo Resistance






STEPPER MOTOR COIL RESISTANCE CHECK


Disconnect the electrical connector at the Idle Speed Control Servo.
Measure the servo's resistance, between terminal # 2 and terminal # 1 and then between terminal # 2 and terminal # 3, at the ISC Servo side of the connector.
Measure the servo's resistance, between terminal # 5 and terminal # 6 and then between terminal # 5 and terminal # 4, at the ISC Servo side of the connector.
Standard resistance:

Between terminal (2) and either terminal (1) or (3) 28-33 Ohms [at 20°C (68°F)]
Between terminal (5) and either terminal (6) or (4) 28-33 Ohms [at 20°C (68°F)]
STEPPER MOTOR OPERATION CHECK

Cautions:


The following test procedures must be followed in the exact sequence instructed. By applying power and/or a ground as instructed, circuits within the servo are activated properly. Skipping a testing step will produce inaccurate results, which may lead to the unnecessary replacement of a component.
Do NOT clamp the servo into a vise.
Assistance may be helpful in completing these test procedures.
Remove the Idle Speed Control Stepper Motor. Refer the COMPONENT REPLACEMENT AND REPAIR for Throttle Body removal procedures.
Checking The Stepper Motor Operation








Connect the positive leads of a 6 volt power source to terminals # 2 and # 5 of the ISC Servo.
While holding the ISC Servo, connect the negative leads of the power source to each terminal IN SEQUENCE. A slight vibration should result at each connection.
Connect the negative terminal of the power source to the ISC Servo connectors terminals # 3 and # 6.
Connect the negative terminal of the power source to the ISC Servo connectors terminals # 1 and # 6.
Connect the negative terminal of the power source to the ISC Servo connectors terminals # 1 and # 4.
Connect the negative terminal of the power source to the ISC Servo connectors terminals # 3 and # 4.
Connect the negative terminal of the power source to the ISC Servo connectors terminals # 3 and # 6.
Repeat the above test procedure in reverse. Starting with step e. and ending with step a.. If vibration is felt at each step procedure, the servo can be considered to be operating normally.

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[Elek_ron_ix]

+2 good posts for the ISC. Would have been good to know when i took mine out Mine was covered in black deposits and had a bad gasket. I cleaned it up and threw a new gasket on it and worked fine. Let us know your results.