DSMISC Automotive


1. What does ISC/ IAV stand for?
Idle Speed Control/ Idle Air Valve/ Idle Stepper Control. Take your pick. All these names refer to the same part on DSMs. We call them ISCs, because that's what most people call them in the DSM community. Stealth/3000GT people call them IACs.

2. Why should I replace my ISC, besides improving the idle?
There is a far more important reason. If your ISC has shorted coils, it will eventually damage your ECU. Shorted coils will fry the drivers in the ECU; it doesn't take a fully shorted ISC to exceed the current specs on the M5269L drivers Mitsubishi used. They are only rated for 2A 10ms 10% duty cycle pulses max. A closed short (meaning low resistance) ISC coil will easy cause it's corresponding ECU driver to load ("sink") many more times than it normally would; eventually the driver exceeds its rated duty cycle, heats up and shorts. As resistance goes down, current flow increases. The old ISC coils are supposed to test at 28-33 ohms. On those, anything below 20 ohms or above 50 (indicating leaning toward an open coil) would be a problem.

Once an ECU driver goes as a result of shorted coil, several ECU IC circuits will be next in line to be damaged. Why risk your $375 socketed ECU by running with a bad ISC?

ecu driversECU drivers are circled in red:

3. My ISC tests ok, but I know it's not working. What gives?
Sometimes, the ohms reading can be in spec but the ISC is still bad. Testing with a 6V battery is a better test (tests the ISC motor), but even then you can't be 100% sure. It could be a mechanical plunger problem as opposed to an electrical coil problem, see below #8. Try taking it out as shown in the video in #12, and see if it operates the same. Another possibility: your ISC O-ring could be missing, or leaking.


4. My ISC is bad. What are my options?

1. Buy a new ISC from DSMISC Automotive.

2. Buy a rebuilt from on-line sources ($40 - $110 + shipping) . 

3. Buy from dealer (about $245 + tax or shipping). 

4. Buying from junkyards and rebuilding your own by picking good coils from junkers. (about $12-30).

5. What cars does the ISC your selling work with?
Mitsubishi Eclipse, Eagle Talon, Plymouth Laser,( 1G or 2G 2.0L DSM's, from '90-'99, turbo and NT), Mitsubishi Galant VR-4 ('90-'94), Pajero and Montero '88-'96, Hyundai Sonata ('94-'95), Hyundai Elantra '95, Mirage/Colt Turbo ('89-'91), or ANY Dodge Stealth/ Mitsubishi 3000GT- 3.0 (turbo or non-turbo).

There are OTHER models too, we are always adding to this list. If you know of some not on the list, let us know!

6. Do I need to replace the O-ring as well as the ISC?
Yes. The o-ring experiences a lot of heat and if your previous ISC was damaged from coolant due to a leaking FIAV seal, it will probably have deteriorated. Over time, the O-ring will either get brittle and crumbly, or it will soak up liquids and inflate in thickness and diameter AND be stiffer than a fresh one, making it a little tricky to get it properly placed back in the FIAV when you need to install your new ISC.

Replace the O-ring! It's cheap insurance, and one less thing you will have to worry about.

7. My old ISC died because coolant leaked from the FIAV seal. Should I put a new ISC in?
ONLY AFTER fixing the FIAV leak. Although the new ISC is a bit more resistant to this kind of failure due to it's coolant-resistant case material, it is not immune to coolant damage. Fix the FIAV seal leak first!

8. My old ISC's coils test fine, but the ISC still seems to be the problem. Idle still fluctuates! What could it be?
The coils aren't the only failure point in the ISC. Many ISC's fail not because of bad coils, but because the mechanical plunger drive wears and gets sloppy in it's movement. If you can rotate the plunger easily with your fingers at all axially around the major axis, it is getting loose and sloppy. 5-10 degrees of movement is common on old ISC's. A new one will not rotate at all. There is no fix for this kind of wear other than to replace the plunger parts with fresh, new ones- providing tight movement and repeatability in the movement of the plunger in relation to the stepper drive commands. Only then can the ECU get the repeatable and accurate responses it needs to fine-tune timing to get a smooth idle. (Of course everything else in your motor needs to be working perfectly also!)

9. The new ISC you shipped me reads 40 Ohms across the coils, not 28-33 ohms. This isn't what the VFAQ, or the OEM manual or other test procedures say.
Yes, because most of the on-line info on DSM ISCs is old and has never been updated! Mitsubishi started putting these new ISC's in cars around 2000. Dealers started selling them as OEM replacements for DSMs after they cleared out their stock of the older units. These older units (cast metal/brown plastic) are impossible to find anymore, and in any event, aren't as good as the new version. The new OEM replacement ISC for the 4G63 motor uses a higher ohm load. This is an improvement over the old ISCs, which were suppose to be within spec if they were between 28-33 ohms. Those cause the ECU to push more current. The new-style ISC's are much more precise and will read about 40 +- 0.25 Ohm across each coil. The higher ohm rating is actually a good thing, and results in pushing your ECU drivers less than even a brand new, old ISC. In other words, it uses less power to do the same thing.

Remember, we sell the SAME ISC you would get from the dealer!

10. Will the ISC you sell work with my Dodge Stealth/ Mitsubishi 3000GT, 3000 SL, etc?
Yes. It is the direct Mitsubishi replacement for both the twin-turbo and non-turbo version. You don't have to spend $353.43 (dealer list) on it!

11. Will the ISC you sell work with my '90 DSM T/E/L? Below section for 89/90 OWNERS ONLY!

We get this one a lot. The answer is yes. The only difference is the 8" "tail" wires and connector that extend from the original '90 ISC. This "tailed" ISC was used on DSM's up until 6/90. After that the "tailess" version was used.

To use the updated ISC we sell with your '90 DSM motor harness, all that is needed is to make an extension cable. There are two ways to do it:

By cutting off the old ISC harness and crimping spade connectors on to each of the six wires so that it will plug into the new ISC. Cut as close to your old ISC as you can, so that the cable extension can be as long as possible.

Or, by just making six wire extensions so you can reach to your '90 motor harness and the new ISC. You'll need spade connectors crimped on either end of each wire (more work than using your old ISC tail).

The six connector pins are identical between the two ISCs. The pin/wire connections are straight through, pin to pin. You don't have to spend $243 (dealer list) on a new '90 ISC!

One more thing. It's easier to install your ISC with the entire throttlebody off the motor. The '89/'90 TB has a 'transverse' setup with the ISC port rotated 90 degrees to the TB flange face. Mitsu makes it hard on this setup to get to one of the two bolts (while the TB is mounted on the intake) holding the ISC to the TB; it's hidden under the TB. Also, (important here) you will need to flip your new ISC UPSIDE DOWN (connector side facing downwards) when bolting it to the TB. An ISC mounted connector-side-up won't fit once you try to put the TB elbow back on the motor-mounted TB... the corner of the TB elbow flange will hit the top of the ISC.

So, flip the ISC upside-down when mounting it to the TB! Then, it fits perfectly!


12. How do I check resistance on my ISC? Checking resistance will tell you if you have a bad coil- below scan is from DSM manual but applies for ALL cars that use the ISCs sold on DSMISC.com. NOTE- These resistance values are for the OLD OEM metal cased ISC, NOT the new black-cased OEM ISC now offered by Mitsubishi, but the pin-outs on both ISCs are identical.

dsm manual resistance

Here is a video showing a good running ISC removed from the throttle body but still connected to the ECU:


13. Can I return my order? I ordered the wrong ISC/ Don't need this ISC/ Need to buy food instead!
Yes you can, subject to the following:

a. You must contact us before you ship in order for us to provide a RMA number for your package.

b. We will provide you a ship-to address with the RMA via email.

c. You will not be refunded shipping costs. Your return is subject to a 15% restocking fee. It will be processed through our inspection process. If the unit has been installed or is otherwise not "new" any more, I can only sell it as used (which I don't do, anyway) in which case another 35% will be applied against your credit amount. IF YOU HAVE QUESTIONS, PLEASE ASK ANYTIME BEFORE YOU ORDER. THERE IS NO DUMB QUESTION!   

After thirty days past shipment date, we do not accept returns.



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