Bad consequences of fixing ISC motor?

[pcons]

Hi, I've got the dreaded idle surge problem in my car, and I've traced it back to the ISC motor on the throttle body. I removed the ISC and applied power to the car (didn't start it though) and noticed that the ISC leadscrew backs out nicely, but won't move forwards. Right now I just removed the electrical connector to the ISC (since it doesn't send any engine trouble codes) and manually set the leadscrew to make the car idle at 1000 rpm with all devices off (the leadscrew is almost fully closed now). If I turn on my blower, rear defroster and headlights, the rpms drop to around 800. Basically, my ISC is now acting as a second BISS, fixed in position instead of variable.

I know the ISC is supposed to normally open and close during engine operation, but I'm wokdering what would be the bad things that could happen by running with the ISC at a constant fixed position. If I'm understanding correctly, it may make a bit of difference in power and fuel economy, but for the most part it is safe for the engine. I'm not sure I want to spend the $300 on a new ISC since I'm probably selling the car in the summer. Its a 91 and its getting on in years. Anyway, any advice would be appreciated.

 

[billdo_83]

Get a new ISC motor. You can get one up from a junkyard or someone that has a parts car.

If a part is broken, then fix it. Its as simple as that.

 

[CurtTSI]

It won't hurt anything, except drivability. However, you can probably find one from salvage or Ebay for only about $50. They usually fail due to one of the two internal coils going bad. I have repaired several by swaping good coils for bad ones. I once bought a perfect ISC on Ebay for $3.50. I bought it for internal parts only but it turned out to be perfect.

 

[monotalonawd]

Pcons, I've been running my 1g without an isc for almost two years and personally, I prefer it that way. My idle is adjusted the same way you did and it never changes. I would leave it that way, especially if you're going to sell it. Just hope that the new owner won't mind it.

 

[boostedinaz]

I was going to go without an ISC but here in AZ the summers get hot so the AC has to come on. You can either get a used ISC, risky at best, or buy a rebuilt one from www.crebotech.com. They are only 80 or so and they come with a gaurantee.

You can also just block of the whole lower portion of the TB with this supernice plate.

http://www.qprinc.com/

You have to go to FIAV blockoff to see it and order.

 

[steve]

There may be nothing wrong with the ISC itself. Check the coils and if they measure good have your ECU checked. I see this happen all the time when C106 has leaked and either eaten the ISC (B2 Coil Pin 68) trace that runs right under it open or has shorted it to +12v and blown the driver.

Steve

 

[me612]

Damn Mike, those BO Plates seem awesome, how'd you hear about those??? j/k, I too have one of those same plates that will be going on my car. I drive it only in summer, so I too have to run my A/C. But I've been running with basically a blocked off ISC like the guy who started this is doing, cuz my ISC is shot. I just set my idle for around 900rpm, and when I use the A/C, it goes down to around 750. Works just fine for me. and no more worries of idle surge caused by those lil bastard ISC's!!

 

[t0taleclipse]

my car has idle surge in the same way as the guy who posted this but when my car idled fine i pulled the connector to the ISC and it never surged again. Does this mean the ISC was bad and one more thing my car doesn't idle higher when its cold, is this normal with ISC unplugged?

 

[me612]

Idling high when the motor is cold deals with the FIAV, not the ISC. The FIAV has coolant running through it. There is a tablet inside the FIAV, and it's state depends on the temp of the coolant. So let say you go outside and start the car, well the motor is cold, so this tablet is hard(frozen so to say), and isn't making a good seal, which allows air to get past it, causing a slightly higher idle. Now once the engine heats up, the coolant gets warmer, melting that tablet. Once it's melted, it will make a good seal (well at least a working fiav will). This will not allow air past anymore, causing your idle to be normal. Now after a long time, that tablet can just get old and not seal like it was designed to do. So you will consantly be getting a little air through there. This could cause idle surge, or also just a higher idle.

Hope that made sense. And you can also block this off if you want along with the ISC at the same time, with that blockoff plate that Mike linked to earlier. Here is a pic of mine, they don't look like the ones on that site anymore, they look like this now, anodized blue. Mike got the last brushed aluminum one.

 

[t0taleclipse]

ok i know how the fiav works but what im saying is my car has idle surge/ high idle sometimes (85% of the time) and when i was idling normal i unplugged the isc connector. Now i dont have it but when my car is cold it does not idle higher with the isc unplugged. Is this normal????? Now this morning my car idled low and stalled so i turned the BISS so it idles at 850 or 900 rpm so it starts and does not stall. Runs normal as it should with the exception of the higher idle at cold start ups. Any idea's ? Is it because I unplugged the ISC ?



THIS IS ON MY 92 LASER RS NON-TURBO