Bad ISC?

[STL91TSI]

Ok heres the situation,

In the morning when I've started up my car its starts up at 2k Idle,(Lower if i kick on AC)
After I drive for 5-10 min the idle will drop down to 1200 ish.
And then randomly, at times the idle will go to normal (750) this only happens id say 20% of the time.

Not in the last few days but last week I had a idle surge a couple times. Would fluctuate between 1200-1500.

So from searching, and based on the fact that when something on my car breaks its always the most expensive, im guessing its the ISC.

Any comments/opinions?

Edit: Almost forgot I get intermitent CEL's. It never stays on very long, it comes on then goes out. It will stay on from anywhere to just a few seconds to maybe 1 minute. But always goes out.

 

[DSM90AWD]

May want to first take a look a the Intake VFAQs relating to the Idle Speed, FAIV and TB Cleaning

 

[RSTurboFWD90]

You can do a quick check of the ISC coil resistance and that will tell you if any are bad. Beyond that a throttle body cleaning should help. Also do a check of the idle switch to be sure it's functioning.

 

[STL91TSI]

Yep ISC is bad, Ohm readings
1-2 - 31 ohm
2-3 - 32 ohm
4-5 - 79 ohm
5-6 - 31 ohm
Bleh....oh well atleast i know whats wrong now.

 

[RSTurboFWD90]

Hopefully that's it. I'm surprised at 79 ohms, (I thought it would be either open or shorted). But either way, it's out of range. You may also want to check it for movement (using a 6-volt battery) after you remove it. Also, be sure to clean your throttle body. Please post your results.

 

[somdturbo]

Eliminate it using jmfab fiav blockoff plate...thats what I did. Those ISC's seem so fragile.

 

[RSTurboFWD90]

Didn't eliminating the ISC affect idling and driveablility? How are you liking the results?

 

[doggo]

Didn't eliminating the ISC affect idling and driveablility?

It does. Removing the ISC means the idle RPM will vary somewhat with temperature and humidity. If you are running A/C, it will drive idle down when AC kicks on.

Here is some cleaning and test info (sounds like at least one of your coils is bad) and isc suppliers:

http://www.stealth316.com/2-isc-iac.htm


Doggo

 

[NitrousBob]

Also remember if the isc shorts it will cause the ecu some problems. Like burning things up inside.

 

[itsover]

I got one for sale pm for detail.