99 GST ECU fried or what?

[KMOSES]

Hey guys,

This project started about 2 months ago, I was experiencing a bad idle, found out my tb shaft seals were leaking pretty bad, replaced the tb, helped a lot with response and power, but idle was still sitting around 1k, even with the BISS screw all the way screwed in...

I pulled the ISC and tested it and got all readings over 45, so I bought a new ISC from a guy on here, when I got the ISC in the mail i tested it and was getting inconsistent jumpy readings, i noticed one of the coils i tested was jumping around way down in the 0.2 - 0.8 range, the readings just never settled, so i figured my multimeter was bad.

I messaged the guy and he assured me it tested perfect before he mailed it to me, so i just put it on, and fire the car up, it bogged and died. I tried it again, and it started up really low idle, really rough, but died again after a bit, then i remembered my biss screw being all the way in, i backed it out a bit and started it up and it stayed on but really rough, so i just backed the BISS out some more until my idle settled around 750. the car now ran but idle was still a little weird.

I turn on the AC and the idle dropped below 500 and almost died, idle went horrid.

Since then I've bought a new multimeter, tested the ISC and got 38, 0.5, 41, 41. pretty similiar results to my initial test with the bad multimeter, So Im guesing this ISC is bad and was bad to being with, now im just hoping it didnt fry my ecu driver.

I pulled my ecu to look and see if its burnt up. However I have no clue what im looking at/for, and I have only been able to find pics/threads on 1g or n/t ecu's that look nothing like my ecu.

Does anyone know where the isc drivers on a 99 gst ecu look like? or where they are located?

thanks!

 

[cwriley]

Well first off what lead you to ecm? there are many different things that can cause bad idle, checked throttle pos sensor? make sure there is no intake or exhaust leaks, is fuel pressure good? before and after fuel filter? all injectors spraying well? i had a wierd idle problem once and it ended up being the sensor on the left side of the tb had 1 wire going to it. you can loosten it up and adjust where you want your idle, i set mine at 1k. (at end of throttle cable linkage stops the throttle plate, not sure if 2g's have this sensor)

 

[KMOSES]

Well first off what lead you to ecm?

I've read on here that a shorted out ISC can blow the driver on the ecu, I just want to make sure my ecu is fine before i put a new ISC on.

 

[gofer]

First things first, the ISC you replaced sounded like it was good from the brief test results you gave. The '99 ISC (black) measures a higher resistance, I think mine measures about 40-45 ohms across the board.

If you installed a bad ISC and any of the coils showed infinite resistance (open) or no resistance (short) then you more than likely need to replace a blown driver. If this is the case I recommend contacting ECMLink and having the test/troubleshoot it for you. They are a supporting vendor and have excellent customer service.

 

[KMOSES]

First things first, the ISC you replaced sounded like it was good from the brief test results you gave. The '99 ISC (black) measures a higher resistance, I think mine measures about 40-45 ohms across the board.

If you installed a bad ISC and any of the coils showed infinite resistance (open) or no resistance (short) then you more than likely need to replace a blown driver. If this is the case I recommend contacting ECMLink and having the test/troubleshoot it for you. They are a supporting vendor and have excellent customer service.

Damn, i already pitched the first ISC i had, I was figured it was bad because the vfaq showed the good range was lower....

all of the coils were good except the one that showed 0.5 ohms, almost no resistance, is that low enough to fry the driver?

 

[KMOSES]

Update,

Got a new ISC, all coils tested good, and im sort of back at square one, 1k idle, it stays pretty steady, its not surging or anything..

tps is set properly.

biss screw is all the way screwed in, if not my idle will go up higher the more the screw gets backed out.

however when i turn on the a/c it still drops the rpms about 200-300 rpms. is that normal?

I got in contact with the guys at ECM and they said they currently do not support the 98/99 ecu, and their knowledge is very limited on them and their layout.

I pulled the ECU, but it looks totally different than any of the pictures i found on here of ECU's with blown ISC drivers,

however I did find some brown goo like substance going across the ecu board.

with all that said, I'm gonna have to lean toward the ecu being bad, what do you guys think?

If so, ill probably have to live with these symptoms for some time, until I can afford a new ecu, ill probably go with a eprom to prepare for my future dsmlink.

 

[KMOSES]

Update,

Threw a CEL today while driving around with the a/c turned ON, CEL came on just a few minutes after i turned on the A/C, I drove all day yesterday with my new IAC with no A/C and it was fine.



Code: P0505

Definition: IAC circuit condition or idle speed higher/lower than expected

Explanation: ECU has detected that the IAC counts are higher or lower than expected, the engine speed is not in its expected range.

Probable Cause:

1. Vacuum Leak on engine ( just did a boost leak test recently and have no leaks )

2. Dirty throttle body ( installed a new one not too long ago, rebuilt, cleaned, sandblasted, looks brand new)

3. IAC motor Defective ( yesterday I installed a brown IAC tested it with multimeter all coils were in range )

4. Poor electrical connection to the IAC valve ( I'm guessing this one is the culprit )



is it possible that the IAC harness/plug is bad? is there a way to test these?

could #4 be pointing to the ECU driver being blown? as its not sending the right signals, because its dead?


side note, the brown IAC wouldn't fit the same way my black IAC did, so i had to flip it around, does that make a difference?

 

[4g63 PowerBlock]

did you solve your problem bro...
cause im idling at 3000k
and i just want to solve the darn problem i test my ISC and everything is good but my connector could be my problem bacuse wheni do the key in the ignition test the ISC doent move not one bit

 

[KMOSES]

did you solve your problem bro...
cause im idling at 3000k
and i just want to solve the darn problem i test my ISC and everything is good but my connector could be my problem bacuse wheni do the key in the ignition test the ISC doent move not one bit

nope, I just unplugged my ISC to make sure i dont burn up another one, and I just adjusted the BISS to where i want it around 900-1k and I just don't use my A/C or anything that messes with my rpms.

 

[nickk90]

If im correct you need link or a scan tool to properly set the BISS on a 2G. If not the ICS will not center itself and will be out of range to control idle.

 

[ed1380]

the 98 and 99 use a programmable ecu. get evoscan $25 or mutmonitor free and a vagcom obdII cable from ebay $15 and you can datalog everything from the ecu. also you'll be able to set the biss correctly.

if you get the tactrix cable $180, you can reprogram the ecu. AKA you will have the modern equivalent of ecmlink for 1/4 the price.

 

[4g63 PowerBlock]

i got a question guys....
well...
im concernd cause
i might have a bad ECU but wen car is cold its hard to accelerate
and points a bad TPS circuit, maf circuit, and other things
but i erased codes and TPS circuit came back...
and well i idle at 3K cause my IAC doesnt get no electricity what so ever...
tps and IAC are BRAND NEW!

 

[KMOSES]

the 98 and 99 use a programmable ecu. get evoscan $25 or mutmonitor free and a vagcom obdII cable from ebay $15 and you can datalog everything from the ecu. also you'll be able to set the biss correctly.

if you get the tactrix cable $180, you can reprogram the ecu. AKA you will have the modern equivalent of ecmlink for 1/4 the price.

All of the vagcom cables I see on ebay say vw/audi, will those still work? also they have a usb on one side, I assume that will that allow me to just plug into any laptop?

 

[KMOSES]

you can datalog everything from the ecu. also you'll be able to set the biss correctly.

Ok, I've got Mut Monitor and Vag-com cable hooked up and im data logging. Now as im monitoring the ECU can I simply adjust the biss screw and thats it?

I feel like i've read somewhere you have to put the car into "Diagnostics Mode" is that possible with Mut Monitor? I've done quite a bit of searching and there doesn't seem to be a lot of documentation on mut monitor.

 

[ed1380]

IIRC you want to datalog the ISC and adjust the biss screw so that the ISC is at a value of 30.

 

[KMOSES]

Made an attempt at this, but im not sure if im doing it right. After adjusting the biss i got the ISC step count to 34, then I adjusted the biss and checked again and it was at 35, so i adjusted the biss in the oposite direction, and then it started climbing, and eventually leveled out at 100, then no matter how i turned the biss it stayed at 100 steps. I'm gonna give it another shot tomorrow, ran out of time today.

But I think I may have a boost leak at the biss, while adjusting i noticed different sounds & pitches of air coming from somwhere...

Going to do a thorough boost leak test before I try again at the ISC adjusting.

 

[jayrec]

For people who are having this problem on "99" eclipses, check your ecu for fried resistors. After re-soldering the new resistors and replacing ISC, cars idle great again. Beats paying $200 for a new ecu.