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2G Is this ISC motor bad even if coils test fine?

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Kryndon

Proven Member
944
591
Jan 10, 2014
Bulgaria, Europe
I made a video of its behavior when turning the key to ACC and then back to ON:

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As you can see, it still moves in and out, however it stopped making that longer whirring noise like it used to before. Also, compared to this video of a working one, it doesn't seem to vibrate in place.

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I tested all 4 coils and they are within the 28-32 ohm range at ambient temp. As soon as the car warms up the idle starts going absolutely batshit. It would start to jump up and down from 1000 to 1500 rpm twice per SECOND, as if I'm constantly dicking around with the throttle pedal. Sometimes it would almost stall, sometimes it would start climbing RPMS.

I have eliminated all other possible causes such as:
Boost leak
Vacuum leak
TPS
Wiring
Clean Throttle body
Binding Cruise Control
Binding Throttle Cable

I am 99% sure the ISC is bad even though the coils test fine. My engine has also been running much hotter after the rebuild and it's already really hot around here so all the additional heat is maybe causing the ressistance of the internal coils to increase so maybe that's why it's shot. I'm searching for a used one currently but I would appreciate some feedback on what you fellas think based on my video. Thanks in advance!
 
I just recently had an issue with a new motor where it was surging horribly as you describe (500-1000 rpm jumps constantly and consistently.) Turned out to be a FIAV issue. Id recommend doing the FIAV bypass, in the future I will be doing this on my other car.
 
What you describe sounds like classic idle surging.
The IPS is stepping in and out like it should but it's on old style original ISC/IAC that are known for shorting out over time I'd replace it with one of the new black plastic parts to be safe.

When did your car begin surging?
 
I'm aware of the inferior quality on the brown top ones, Steve. I've been searching furiously over the past few days for a black plastic one but there ain't none from an Eclipse. I'm finding lots of identical looking ones from other models such as Galants, Colts and some Hyundais but I cross-reference CAPS and the part numbers for both ISC models for the DSM are different to those on other models. That said, they might be identical internally but I cannot risk it, unless someone can confirm with part numbers whether non-DSM ISCs work on ours.

She started surging last week (when ambient temps finally rose to around 80F). As soon as the car got hot (she's running hotter now because my FMIC blocks a lot of flow), the RPMs just go mad. It's also throwing a PENDING P0505 Idle Control Malfunction. Oddly enough, when I got the car all back together after the engine rebuild (earlier in March when it was still cold), that P0505 code popped in once but I erased it and didn't have idle issues at all. I did however install a proper EGR block off plate (sealed with RTV) and cleaned the throttle body thoroughly. I also installed all new gaskets such as an intake manifold gasket, and a TB gasket. There seem to be no boost leaks, but even if the surge was due to a leak, it would have been happening as soon as I went for the break-in.

Like I said, it recently got very warm around here and the coolant while cruising goes up to 222F, however I am flushing the old coolant right now and putting in fresh new one + distilled water, so I'm hoping that would drop temps down further. My thinking is that this ISC is simply becoming much more susceptible to heat, and as soon as the engine warms up it the radiant heat increases the resistance of the coils which makes it act up. I'm no electrics engineer but that's what I'm thinking. While it was still very hot I took it off the car and measured the pins. 1 and 2 gave 32 ohms, whereas 3 and 4 measured 33 ohms. I later tested them again while cool and they measured 30 ohms.

I started thinking about what greddy_1700 said about the FIAV. Could the increased coolant temp f*** with the internal spring and make it malfunction? I'm not 100% sure how the FIAV works in relation to the ISC but that may also be the culprit. Or if the ECU driver controlling the ISC has been blown randomly. I admit I have messed with the BISS before but always turned it 1/4 turn very slowly. I don't have Link so I can't control or ground it that way.

I'll be topping off the coolant tomorrow and hopefully a guy locally will give me another brown top ISC to test out. I'll get back with results, but in the meantime if someone else has any other ideas, please feel free to chime in!
 
Small update, but still no good results. A friend gave me a spare one he had (brown top again). All pins tested fine besides 5+6, that didn't read any ohms so it must be an open/faulty coil. What I tried to do was combine the good 1st coil from his, and the 2nd coil from mine. In doing so I actually learned how the mechanism works. There is a cylindrical magnet and a threaded shaft in the center, with 2 support bearings. The shaft is attached to the plunger. Essentially the electric current makes the magnet either go forward or back, thus it forces the threaded rod inwards or outwards, which allows the plunger to move in and out basically.

However, after installing this new frankenstein ISC (again, all pins/coils tested ~30ohms), with the BISS prematurely set 2 revolutions OUT (standard position), the RPMs shot up to 2k, slowly dropped to about 1500 (with no accessories) and stayed there. What surprised me that even BEFORE starting the car, from doing ON>ACC, ON>ACC to test the ISC, the ISC got really hot. Could too much current be flowing through it, causing it to malfunction? I did open up my ECU but the drivers were completely intact, no smells, no leaks, no breaks in the circuitry. I let the car warm up idling without touching anything. At 88C the thermostat opened, the new coolant started flowing fully through the radiator and both hoses got really hot. As soon as I started reversing out of my driveway the RPMs started surging again. 1000>1500, 1000>1500 etc. I went to the car wash to give it a rinse anyway and threaded the BISS 1 full turn INWARDS. That made no difference to the RPMs. I even fully slacked off the throttle cable bracket just to make sure it wasn't binding or anything from the heat, but no results either. I touched the ISC again but it was extremely hot. I have the EGR blocked off completely so no exhaust gasses should flow through it.

I also got the P0505 code again.

Later today another guy is gonna give me an ISC to test out. Wish me luck but I'm starting to lose hope.
 
I'm going mad. The 3rd ISC I tested had one coil reading 164 ohms... Waay to much resistance. So again I made a 'healthy' ISC from combining a good 1st coil with a good 2nd coil. I resoldered all the connections, made sure everything is clean and dry. Hooked it up, deleted any codes, reset the ECU/battery and went for a drive. Again, as soon as I started reversing the idle started surging. I got so mad I beat on the damn car quite a lot. It runs really strong but as soon as I go into neutral the RPMs either climb to 1500 and stay there, or they start surging between 1k-1.5k.

I double checked to see if my FIAV coolant lines are mixed up (I was unsure), but they are not. I made sure the o-ring is intact and well seated in the ISC spot. I rechecked my throttle cable bracket, it has maximum travel while having enough slack.

I am really lost. I have no clue what it could be. I don't think this car ever had a normal idle, like ever. I remember before the rebuild, on a cold start it would rev up to 1500 and immediately drop to my desired 850 RPM, WHILE COLD!!

I f***ing hate the shitty electronics they put on these cars. The engine is going to get wrecked from all this unnecessary high idling at stop lights this Summer. Way too much heat and wear. If anyone has any ideas I'll be glad to hear them. But I think it's safe to assume it's not a faulty ISC.

EDIT 08/05/2019: Small update. The day after trying out the third ISC, the weather worsened and ambient temps dropped to about 60F. The previous days were really hot, reaching up to 80F. She started up fine, dropped the RPMs a bit to soon considering it was still warming up but it didn't surge. It was behaving like it used to, which was fairly normal without any issues regarding the RPMs. Even with the car fully warmed up, when going into neutral the idle fell back to my target 800 or so RPMs.

Could this be coincidence? Or could the ambient weather be playing a significant role in this? Maybe the temp sensor within the MAF is related to this. I'll drive it like this for now. If the problem comes back when the weather gets hot again then it's definitely something related to ambient/air temp.
 
Last edited:
Last update (27/06/2019) EU format LOL: Been over a month. I believe it was a combination of bad (old) coolant keeping my operating temps higher than normal, causing the FIAV to malfunction (metal spring/wax not acting as designed), as well as bad coils on the previous motors. I did manage to combine 2 good coils into one brown top ISC. I drained the old coolant out and put in new, high quality blue one with some distilled water, 30-70 mix. The weather's been even hotter now but there have been absolutely no problems with the Idle. It starts up fine, idles fine when cold/hot and at stoplights.

In conclusion, I would say firstly troubleshoot the ISC. Even if it tests fine on all coils, it may not do so when its gotten very hot from the engine (radiant heat will heat up the coils inside, increasing their electric resistance). Try a different ISC and run the car to operating temp to see if anything fluctuates. If nothing changes, proceed to troubleshoot your COOLING system, since the idle is also controlled by the FIAV body right under the TB. Bad coolant, air bubbles or simply insufficient cooling might affect the idle RPMs.

Hope this is of help to someone down the line.
 
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