1G Idle Speed Control not Good !!

[emanuele]

Hi,
I have a problen with Idle speed control in My 1G Eclipse Turbo AWD 1991.

I would like to be have a help about my problem:
When my car is running at the idling occurs that the number of revolutions of the engine vary intermittently between the value of 1500 rpm and 1800rpm.
I tried to replace my old ISC Motor with a used plastic but the problem remains.

 

[Cushman]

Your problem can be the result of a multitude of issues. First, if it has never been done, you may need your throttlebody rebuilt. This is a good cleaning, new shaft seals, new o-rings, new biss screw, and proper adjustment of the isc and the tps. I recommend throttlebodys.com. They have rebuilt two of mine. Part of the throttlebody, the FIAV, is where coolant moves through to heat up the air. The valve in it may not be working properly. Sometimes a rebuild of the tb, and good cleaning of the FIAV will cure it.

Your isc may be bad, even the 2nd one. If you know how you can test it with a multi-tester tool. Your ips may also be bad or need adjustment. Throttlebodys.com will test both of these during the rebuild and if necessary will supply used tested and approved ones.

Make sure your system is filled with coolant. With the engine cold, take off the radiator cap and fill to the top. Fill the coolant container bottle to the full mark.

Your vacuum lines may have a leak. Considering yours is a 91, if never replaced you may have a bad rubber line leaking vacuum.

Hope this helps.

 

[9!'clipseDOHC]

There is a very easy way to test your ISC. Remove the 2, 8mm blots holding the ISC to the TB but leave it plugged in. Have a friend (or anyone really) turn the key to the "on" position and then back off several times, your ICS should turn in and then back out each time the key is turned "on". Check out this video to see what a working ISC looks like. I'd say about half of the 1g ISC are shot.

YouTube - DSM ISC

Also like cushman mentioned, this is a very common problem and there are several other things that can cause it. A few are, Dirty TB, leaking vacuum lines, bad or not adjusted BISS screw, BISS o-ring, FIAV, bad caps on the ECU, etc. Take it one step at a time.

Hope this helps!

 

[DSMGary]

Your problem can be the result of a multitude of issues. First, if it has never been done, you may need your throttlebody rebuilt. This is a good cleaning, new shaft seals, new o-rings, new biss screw, and proper adjustment of the isc and the tps. I recommend throttlebodys.com. They have rebuilt two of mine. Part of the throttlebody, the FIAV, is where coolant moves through to heat up the air. The valve in it may not be working properly. Sometimes a rebuild of the tb, and good cleaning of the FIAV will cure it.

Great Info cushman... I dont mean to highjack the thread but does anyone know of a vender that sells a rebuild kit for the T.B. ?

 

[AlaskanDsm]

Obviously each car is different but does anyone know what the average steps the ISC is supposed to be at during warmup without your lights/AC/etc on?

 

[tsi1991awd]

I am not sure about during warm up, but I know at idle when it is fully warmed up, the ISC should read closer to 0. Because 0 is fully extended and 100 is fully retracted (like during WOT) I am battling with my ISC as well. WIth the ignition on the plunger doesnt move.

 

[AlaskanDsm]

Oh ok. I wasn't aware of that fact. I am having idle surge and am trying to identify the problem. Still suspecting the ISC .

 

[snowborder714]

Test it with a multimeter. Very easy way to tell if it's bad or not. If it tests out fine and you're still having ISC issues, you need to look at the ECU as there may be an issue with the drivers.
DmTaLoN's Idle Speed Control Test/Fix Page!

 

[9!'clipseDOHC]

Great Info cushman... I dont mean to highjack the thread but does anyone know of a vender that sells a rebuild kit for the T.B. ?

There is no rebuild "kit" that I have seen. You need a BISS screw, BISS o-ring, ISC o-ring, FIAV waffle gasket, both throttle body gaskets, and throttle body shaft seals. They can be ordered from JNZtuning, STM, or Extreme PSI.

 

[AlaskanDsm]

Test it with a multimeter. Very easy way to tell if it's bad or not. If it tests out fine and you're still having ISC issues, you need to look at the ECU as there may be an issue with the drivers.
DmTaLoN's Idle Speed Control Test/Fix Page!

Thanks for the link But I have used this page before to test my ISC and the coils test out ok for Ohms and I tried using a 6volt battery but I couldn't really see any movement. Wouldthe best way to test the ISC at this point be to have a second person turn the key to one when I have the ISC out and plugged in?

Not to thread jack...

 

[tsi1991awd]

Thanks for the link But I have used this page before to test my ISC and the coils test out ok for Ohms and I tried using a 6volt battery but I couldn't really see any movement. Wouldthe best way to test the ISC at this point be to have a second person turn the key to one when I have the ISC out and plugged in?

Not to thread jack...

I second this. Coils tested out at 38 across each one. But when the key was turned on, the plunger didn't move at all. I heard a click and felt the click while holding onto the ISC but nothing moved.

I have idle surge ONLY when the car is warmed up...until then, it will idle normal. I suspect ISC, as everything else on the car checks our just fine. I have no clue. This is the new style black plastic one.

The ECU was sent out to ECMTuning to have the eprom conversion done and they tested everything there. There was one trace that was damaged that they fixed. Shouldn't have any problems at the ECU for me....they went over it and said everything was good.

 

[AlaskanDsm]

My car only does it during the warm up phase. I just rebuilt the TB with new shaft seals, new Biss screw, o-ring, cap, and gaskets. It could be the FIAV or boost leak but seems similar situation to TSI1991awd, as I thought I eliminated the boost leaks.

 

[tsi1991awd]

I did the same thing. New shaft seals, new biss screw, biss o-ring, throttle body gaskets, etc. I had 2 boost leaks that I fixed and EGR and FIAV are blocked off. So I really don't know where to look except for the ISC.

 

[GST98 PR]

Test it with a multimeter. Very easy way to tell if it's bad or not. If it tests out fine and you're still having ISC issues, you need to look at the ECU as there may be an issue with the drivers.
DmTaLoN's Idle Speed Control Test/Fix Page!

hey thanks a lot for the link, it really helped me !

 

[AlaskanDsm]

I did the same thing. New shaft seals, new biss screw, biss o-ring, throttle body gaskets, etc. I had 2 boost leaks that I fixed and EGR and FIAV are blocked off. So I really don't know where to look except for the ISC.

We just fail sir.

 

[tsi1991awd]

We just fail sir.

I am going to go out and log the car from startup until it surges and see what the ISC is doing. I was talking to Dave W. (pneumo on the board) and he was saying at idle, the ISC should be zero'd out.

On the 3S page, it says the ISC should be relatively low, around 10 or so at idle and that they've never seen it go down to 0.

So I am assuming if it remains constant, the ISC is good...if it is all over the place during surge then you know it is the ISC.

Simple test just looking at the logger....and I can buy one for $70 brand new so I will do that today if it is bad.

 

[RoasT BeeF]

The ISC's position is ultimately dependant on where you have the BISS set. Adjust the BISS and the ISC will (should) move accordingly.

 

[AlaskanDsm]

Let me know your results as I will have to get my logger hooked up tonight as well and check it but that might only be at idle...

 

[steve]

I was talking to Dave W. (pneumo on the board) and he was saying at idle, the ISC should be zero'd out.

On the 3S page, it says the ISC should be relatively low, around 10 or so at idle and that they've never seen it go down to 0.

If Dave W. really said that he was wrong.

At idle with the car at temp, grounding the timing check connector and DLC mode pins sets the ISC to around 12 steps for you to adjust the BISS to the programmed idle speed. The ISC should stay around that when you unground the pins. I typically adjust mine to about 20 steps at idle without touching the connectors.

A reading of 0 indicates that the ISC can't close the bypass air channel any farther and I believe 120 is about as far as it can open the passage. If the ISC steps are at either of these extremes when the car should be idling it's likely it's not working anymore.

The ECU has no feedback on the actual position of the ISC just what it stepped the ISC to. The feedback it the RPM vs target RPM so if it can't get the idle up to where is should be the steps increase to the limit and if the idle is higher than programmed the steps go to 0 because the ECU tried to slow the engine down with no success.

Keep in mind that the ECU also has to see the IPS close to know that it's supposed to be controlling the RPM and the car needs to be not moving. (No pulses from the VSS)

 

[tsi1991awd]

If Dave W. really said that he was wrong.

At idle with the car at temp grounding the timing check connector and DLC mode pins sets the ISC to around 12 steps for you to adjust the BISS to the programmed idle speed. The ISC should stay around that when you unground the pins. I typically adjust mine to about 20 steps at idle without touching the connectors.

A reading of 0 indicates that the ISC can't close the bypass air channel any farther and I believe 120 is about as far as it can open the passage. If the ISC steps are at either of these extremes when the car should be idling it's likely it's not working anymore. The ECU has no feedback on the actual position of the ISC just what it stepped the ISC to. The feedback it the RPM vs target RPM so if it can't get the idle up to where is should be the steps increase to the limit and if the ild is higher that programmed the steps go to 0 because the ECU tried to slow the engine down with no success.

Keep in mind that the ECU also has to see the IPS close to know that it's supposed to be controlling the RPM and the car needs to be not moving. (No pulses from the VSS)

WHen the car first starts up in the morning to warm up, the ISC reads 120. EVen with the BISS screw tightened all the way or loosened a few turns. Once the temp gets to a certain point, the idle raises to 1500 and the surging begins, fluctuating between 1400 to 1600. I check the logger and it WAS giving me different readings for the ISC and then it went to 0.

For some reason the VSS is giving me readings randomly even though the car is in neutral and the ebrake is up. It blips numbers here and there. No clue why.

So would it be safe to say the ISC is to blame for my surging idle? There is nothing else to look at, according to all the things I have read about idle surge.

 

[steve]

What happens during initial startup and warmup is different, that's why I stated at idle at temp.

Depending on the ECT the ECU opens the ISC pretty much all the way to aid in starting and you'll normally see the steps ramp down to 0 or so shortly after it starts and then back up to the 12-20 range once the FIAV starts closing.

If you using MMCd and trying to use the VSS that it displays you not really reading the VSS, what you'll see will look pretty random, the memory location that MMCd uses isn't the VSS counter in a DSM.

If your not idling at 750 with a stock ECU or what you programed with aftermarket software you can bet that the ISC steps will be 0 or 120 depending on if the idle is higher or lower than what's programmed.

 

[sexystover]

i had an idle surge problem after warm up and hard starting when cold, tested the ISC and one coil was bad, replaced the isc today and she starts/warms up/idles perfect now , i used the vfaq guide for testing

 

[VIGILART]

I bought an eprom ecu from someone used and my car had idle surge when I installed it, so I sent in the ecu to ecm tuning and they replace the drivers for the isc motor. they said the isc motor was bad on the car I got ecu from and blew the drivers. Idle surge fixed!

 

[tsi1991awd]

What happens during initial startup and warmup is different, that why I stated at idle at temp. Depending on the ECT the ECU opens the ISC pretty much all the way to aid in starting and you'll normally see the steps ramp down to 0 or so shortly after it starts and then back up to the 12-20 range once the FIAV starts closing.

If you using MMCd and trying to use the VSS it displays you not really reading the VSS, what your see will look pretty random.

If your not idling at 750 with a stock ECU or what you programed with aftermarket software you can bet that the ISC steps will be 0 or 120 depending on if the idle is higher or lower than what's programmed.

FIAV is blocked off. Idle will sit like it is supposed to until warmed up and once it is warmed up, it will surge. I believe idle was set at 850 on the eprom chip. But when it surges, ISC goes down to 0. When I unplug the ISC, nothing happens, still surges. So I don't know.

 

[steve]

FIAV is blocked off. Idle will sit like it is supposed to until warmed up and once it is warmed up, it will surge.

Without the FIAV you shouldn't have much of a fast warmup idle. Since the ECU programmed idle and decel cutoff limits are higher when the ECT is low to allow the FIAV to fast idle your not hitting the decel cutoff when cold. As the coolant temps rise the values in the table drop just like the idle speed is expected to and at some point your crossing the line and surging starts.

I believe idle was set at 850 on the eprom chip. But when it surges, ISC goes down to 0. When I unplug the ISC, nothing happens, still surges. So I don't know.

Why would you expect unplugging the ISC would make any difference. It's not like it's spring loaded and disconnecting it would cause it to move.

Does your ISC pintle move in and out when you turn the ECU on like in this video? If it doesn't then the ISC system is not working correctly.

Does the IPS have a good ground connection and pull the voltage on the green wire to 0 when the throttle is closed and sit at > 5v when the throttle is opened. If it doesn't the IPS isn't working correctly.

Do all four coils in the ISC measure between 28 and 38 ohms? If not the ISC is bad! It can still be bad if they do since this only tests the coil windings and not the bearings or pintle screw thread.

You must be logged in to view this image or video.

If the ISC works you have a bypass leak somewhere. They are harder to find since a pressure test only identifies external leaks so you may still have air sources to the intake after you have found all the external "boost" leaks.