ISC/IACV issue

[Sniffbooger]

Hi all, my first post in a DSM forum, as I usually tinker with Hondas and Toyotas, but I bought my Eclipse GST with ideas of making a fun daily driver....it has a 6 bolt swap already installed but the previous owner didn't get it running very good and I bought it for cheap... so now I'm going thru it trying to address the issues.

I was able to get it started after replacing the Engine Coolant Temp sensor and fixing some vacuum leaks. It still idles very rough and surges however. The exhaust smells rich. Exhaust leaks at the header. New exhaust studs coming soon. Two are stripped, and one is broken off... I removed and cleaned the VAF/MAF sensor with alcohol, but it may need replacing... Not tested yet...the 1g IPS sensor is acting as the throttle stop screw, not hooked up. May be in need of proper setting as a throttle stop.

My main question is in regard to the ISC/IACV motor... It's a flat brown one with 3 screws and a 6prong connector. Does anybody know if this is a 1g Eclipse ISC? Or what year/model the lower throttle body and FIAV is from? Are the 1g/2g interchangeable?? I suspect it may be faulty, and I would rather have a newer black one... and if the fast idle air valve is bad, would I need to replace the entire lower throttle body assembly...any suggestions? Looking to make the car run/start more reliably. Thanks!

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[DSMPT]

You actually disassembled the ISC. To remove a ISC completely from the throttle body, you only remove the two 8mm head bolts in the green circles in the pic below. And you have a 91-94 throttle body and ISC, and you can use a black one, too. Should check your ISC before buying another one according to the last pic below.

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[Sniffbooger]

Ahhh yes! My oversight! I actually just noticed that while looking at the pictures as you were responding ...So I'm going to view a couple of videos too and test it see if the movement is correct and also if my ECU drivers are functional.... I may order just the black ISC motor if needed. Hopefully this will cure some of the issues. Ill update as I go! Thank you for the nice diagnostic diagrams....and for replying! DSMtuners rocks!

 

[steve]

Order a black one even if that one is currently "good". The original Metal ISC has a high likelyhood of the coils shorting and that damages the drivers in the ECU. Better to remove that potential problem.

 

[Sniffbooger]

You guys really make a newbie feel welcome! I've been reading countless threads here for months, learning about all the nuances of these Eclipse motors and trying to remedy the issues of my new GST....and its no joke whenever I've read a post by the hallowed Steve, I've learned a lot of good info! Probably even more informative than my newly acquired FSM! It is an honor to have your input on my thread!

I am definitely going to order a new black ISC motor. Found an OEM one on ebay for $83 shipped....not sure if i trust the cheaper Chinese ones for $10... I've already replaced the ECT sensor and TPS with OEM quality. So far so good...I really hope this will do the trick...along with the new exhaust manifold studs and gasket I ordered last week... haven't even taken it out for a spin yet!

 

[Vegas Smith]

You guys really make a newbie feel welcome! I've been reading countless threads here for months, learning about all the nuances of these Eclipse motors and trying to remedy the issues of my new GST....and its no joke whenever I've read a post by the hallowed Steve, I've learned a lot of good info! Probably even more informative than my newly acquired FSM! It is an honor to have your input on my thread!

I am definitely going to order a new black ISC motor. Found an OEM one on ebay for $83 shipped....not sure if i trust the cheaper Chinese ones for $10... I've already replaced the ECT sensor and TPS with OEM quality. So far so good...I really hope this will do the trick...along with the new exhaust manifold studs and gasket I ordered last week... haven't even taken it out for a spin yet!

The most common problem on these cars is idle surge and general idle issues. It's also the most complicated to fix as it involves air leaks and adjustment of multiple sensors. It an be frustrating for a newbie but doable to fix.
This is your DSM idle bible:

https://www.sixsigmatuning.com/dsm-idle-control

 

[pauleyman]

Hi all, my first post in a DSM forum, as I usually tinker with Hondas and Toyotas, but I bought my Eclipse GST with ideas of making a fun daily driver....it has a 6 bolt swap already installed but the previous owner didn't get it running very good and I bought it for cheap... so now I'm going thru it trying to address the issues.

I was able to get it started after replacing the Engine Coolant Temp sensor and fixing some vacuum leaks. It still idles very rough and surges however. The exhaust smells rich. Exhaust leaks at the header. New exhaust studs coming soon. Two are stripped, and one is broken off... I removed and cleaned the VAF/MAF sensor with alcohol, but it may need replacing... Not tested yet...the 1g IPS sensor is acting as the throttle stop screw, not hooked up. May be in need of proper setting as a throttle stop.

My main question is in regard to the ISC/IACV motor... It's a flat brown one with 3 screws and a 6prong connector. Does anybody know if this is a 1g Eclipse ISC? Or what year/model the lower throttle body and FIAV is from? Are the 1g/2g interchangeable?? I suspect it may be faulty, and I would rather have a newer black one... and if the fast idle air valve is bad, would I need to replace the entire lower throttle body assembly...any suggestions? Looking to make the car run/start more reliably. Thanks!

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Do not clean the maf sensor. These are not a hotwire sensor and do not require cleaning like those do. It is a Karmann Vortex sensor. Maf sensor cleaners will even say on the can "not for karmann vortex".
You may also have problems with random misfire using a 1g cas and no tuning solution. You're on the right path fixing what is wrong. 2g does not use an idle position switch. It uses TPS for this if memory serves. Not sure how using a 1g TPS would affect things. I've not personally done it so some research would be in order.

 

[Sniffbooger]

Wow Vegas smith! Thanks for that DSM idle Bible... that is gold! It's written very clearly and coherently. That gives me a really good idea what I'm trying to accomplish here.... Not sure I can afford the dsmlink just yet.... So I'll have to settle for the factory setup best I can, merging the 1G/ 2G throttle body / TPS sensor/IPS delete. Thanks for chiming in I appreciate your input greatly!

Pauleyman!! The wiseman speaks! Glad to read your post! Unfortunately the previous owner already tried cleaning the MAF sensor, and I read somewhere that it was okay to clean it with denatured alcohol lightly and I did it again myself..... But it hasn't made any difference...car still doesn't start easily, idles like crap, and does not accelerate well, so I will replace it if necessary later... For now I will replace the ISC and then try to set the throttle stop, and then adjust the TPS. Also that exhaust manifold studs and gasket set...

Specifically I have two questions....
1) where would I set the IPS as the throttle stop screw? I would think it need to be a little less of a turn after contacting the throttle... Because this is a larger-diameter 1G throttle plate that replaced the smaller 2G throttle body, so that means more air will already be bypassing the plate correct? The DSM idle bible says to turn it 15/16 of a turn beyond when it touches the throttle plate. Maybe I should turn it a little less because this is a larger 1g throttle plate going on the smaller 2G intake?

2) I noticed the original TPS only had three prongs because it was 1G. I have replaced it with a new 2G TPS with four prongs, in order to accommodate the idle switching. However since I've done this, it runs even worse.... I hope I can get it dialed in once I replace the ISC...

Just got my new exhaust manifold studs today... from ebay for $20 shipped....still awaiting my new ISC solenoid... can't wait to get them installed and get it running...at least so I can take it for a drive around the block!!

 

[steve]

Specifically I have two questions....
1) where would I set the IPS as the throttle stop screw? I would think it need to be a little less of a turn after contacting the throttle... Because this is a larger-diameter 1G throttle plate that replaced the smaller 2G throttle body, so that means more air will already be bypassing the plate correct? The DSM idle bible says to turn it 15/16 of a turn beyond when it touches the throttle plate. Maybe I should turn it a little less because this is a larger 1g throttle plate going on the smaller 2G intake?

2) I noticed the original TPS only had three prongs because it was 1G. I have replaced it with a new 2G TPS with four prongs, in order to accommodate the idle switching. However since I've done this, it runs even worse.... I hope I can get it dialed in once I replace the ISC...

I suggest adjusting the 1G IPS to where it contacts the throttle arm but doesn't begin to open the blade. You want it to keep the blade from biting into the throttle bore but not hold it open any. This forces all the idle air to flow through the ports, ISC, FIAV, and BISS passages. Any excess air will cause issues trying to get the engine to idle low enough and surge.

The 2G IPS is inside the 2G TPS and the adjustment is per the factory procedure where you adjust the TPS for where it's IPS opens and closes. I can't find the link to it right now but it involves using a feeler gauge to hold the butterfly open a set amount and adjusting the TPS to cause the IPS to switch at that point.

 

[Sniffbooger]

Thanks!
I found this from an old thread from 2010:
https://www.dsmtuners.com/threads/how-to-adjust-the-throttle-position-sensor-tps.324431/

1. Loosen the 2 TPS screws.
2. Put a feeler gauge of .0177" under the stop screw
3. Turn the car to the ON position
4. Rotate the TPS until pins 3 & 4 lose continuity (open)
5. Verify that the voltage between pins 2 & 4 is .4-1 volt with the feeler still in.
6. Tighten TPS bolts and remove feeler gauge

Is this method above better than setting the TPS voltage at .63 as explained in the DSM idle bible?

1. With key on engine off, check the voltage on the output pin of the TPS connector. Alternatively, look at the TPS voltage in the ECU on a data logger or scanner.
   
   
2. Loosen the 8mm bolts and adjust the TPS until voltage reads 0.63v, and tighten the adjustment bolts.
   
   
3. Verify idle switch operation
   

 

[Sniffbooger]

I suggest adjusting the 1G IPS to where it contacts the throttle arm but doesn't begin to open the blade. You want it to keep the blade from biting into the throttle bore but not hold it open any. This forces all the idle air to flow through the ports, ISC, FIAV, and BISS passages. Any excess air will cause issues trying to get the engine to idle low enough and surge.

This is what I intended to accomplish today... However, after I installed the new ISC today, things didn't work out so well...I discovered after testing the resistance on the # 3&4 pins, my new TPS doesn't work as it should? According to the instructions above, it should have a point where the continuity breaks as the throttle is moved about .0177" from the stop.
However, with my new (OEM) TPS, the resistance just gradually goes from about .45 ohms fully closed, to approx 1ohm, when my continuity beeper stops sounding... The throttle actually moves about 1 full cm before continuity is gradually broken...It doesn't seem like its supposed to be this way....a gradual increase in resistance as the throttle opens up? Strange...

So, I tried the other way above from the DSM idle bible...with throttle stop set just where the butterfly valve is almost fully closed...I measured the voltage between pins #2&4 with key on, and turned the TPS until it showed 0.63v. However, this position was maxed all the way clockwise! And it gave some crappy acceleration with slight puking and backfires. The attached photo shows the maxed out TPS.

So, I'm kinda stuck...the newly installed (OEM) ISC and ECT seem to work, because the car starts much better than before. Probably the FIAV works too? But I'm not sure if this is how the TPS is supposed to behave. I'll tinker around with it some more tomorrow and back off the TPS counterclockwise and see if I can get some better results.... this TPS doesn't even measure 5v when wide open. It maxes at 4.68v. Strange...

 

[Sniffbooger]

I messed with the car some more today, tried moving the TPS clockwise but the acceleration became worse...after it was warm, I disconnected the battery 30 seconds to reset the ECU, then i quickly started the car and backed out the BISS screw to increase the idle rpms because the idle was a too low...but the ecu learned and then it started surging.... plus the engine dies after light acceleration when i back off the throttle...maybe a lean condition at closed throttle...could the ISC be maxed out? I tried changing the throttle stop screw slightly also. I tried different positions for the stop screw, all within one turn of completely closed.

Im going to do some boost leak/vacuum testing and see if there's something I missed...I installed the new EGR blockoff plate today (photo 1) and replaced all the vacuum caps (photo 2)...I am suspecting the throttle plate bushings may need replaced...there is a slight shaft play at the cable side (photo 3)...and I discovered the alternator isn't charging the battery so I wonder if this is contributing to the problem too...

 

[steve]

I'm not sure what you call pins 3 and 4 and the ones that the manual reference are the same. Pin 3 has a yellow with red stripe wire and the wire to pin 4 is black. Pin 4 is the ground connection used by both the IPS and the TPS. The TPS resistance is measured between 2 and 4. (Brown w/red stripe and the same black from above)

 

[Sniffbooger]

I'm not sure what you call pins 3 and 4 and the ones that the manual reference are the same. Pin 3 has a yellow with red stripe wire and the wire to pin 4 is black. Pin 4 is the ground connection used by both the IPS and the TPS. The TPS resistance is measured between 2 and 4. (Black w/red stripe and the same black from above)

I believe the output wire is actually Brown/red stripe not black/red stripe. I am sure I checked the voltage and resistance with the proper wires. My black wire (#4) is on the very top of the connector, unlike the FSM diagram which shows the black wire in between # 2&3. However, the position didn't change the testing procedure.
1) I checked voltage between black and brown/red stripe (#2) wires, but .63v setting was maxed clockwise.
2) and I checked resistance between black and yellow/red stripe wire (#3), but the continuity was not broken until the throttle moved at least 1cm. It was a gradual increase in resistance, not like a switch that is turned on/off when throttle is moved .045mm as described in the procedure.

Still not sure why my new TPS doesn't act as described in the setting procedure....any ideas? I'm not sure why my black and yellow/red stripe wire locations don't match the FSM diagram...is this a problem? There was a 3-pin 1g TPS on there before... but I believe the black #4 ground wire is located the same place (at the topmost pin)??

 

[steve]

I believe the output wire is actually Brown/red stripe not black/red stripe.

You are correct, I've updated the post.

I am sure I checked the voltage and resistance with the proper wires. My black wire (#4) is on the very top of the connector, unlike the FSM diagram which shows the black wire in between # 2&3. However, the position didn't change the testing procedure.

While the diagram shows the TPS drawn with pins 1, 2, 4, 3 that's to make it clear how things internally work, The pins are numbered in order and as you note in this case pin 4 is the closest to the top of the TPS as installed.

1) I checked voltage between black and brown/red stripe (#2) wires, but .63v setting was maxed clockwise.
2) and I checked resistance between black and yellow/red stripe wire (#3), but the continuity was not broken until the throttle moved at least 1cm. It was a gradual increase in resistance, not like a switch that is turned on/off when throttle is moved .045mm as described in the procedure.

Still not sure why my new TPS doesn't act as described in the setting procedure....any ideas? I'm not sure why my black and yellow/red stripe wire locations don't match the FSM diagram...is this a problem? There was a 3-pin 1g TPS on there before... but I believe the black #4 ground wire is located the same place (at the topmost pin)??

I'm not sure why you are getting the results you are either. I hope I've explained the numbering. Just look at how the FSM shows the ECU pins and it should be clear that they are in number order not drawing order. (except when you're looking at the connectors at the bottom of each diagram.

 

[Sniffbooger]

Today, since the battery has not been charging, I traced the 5mm white wires coming from the alternator to the battery and junction box...one wire had broken connection at the battery terminal and a couple other smaller wires from the 4-wire alternator plug had exposed wires under the tape. Apparently the alternator plug was changed and spliced into the 2g harness. Maybe that had something to do with the 6bolt swap...but the splice was not very good so I cleaned it up.

Afterwards the battery showed 14+ volts when running so i thought I had fixed the charging issue. However after a few minutes it stopped charging again. It ran for awhile from the battery as it drained, but I imagine the ecu would have issues without proper voltage....so I shut it down....

As I was tinkering, with TPS set at .63v, i got the idle to stop surging with the BISS screw only 1/2 turn out from bottom. But it smelled rich. Also, it would stall and die after quick acceleration/letting off throttle. And I slowly raised the rpms steady until 2000 RPMs then suddenly the dash battery light flashed red and suddenly the rpm dropped off badly...then it surged and idled roughly...it's only pulling 5-10 lbs vacuum, depending on rpm and BISS/throttle plate settings. I'm waiting for my boost leak tester and new alternator to arrive. From reading around the forums, I'm suspecting throttle shaft seals and probably the FIAV (fast idle air valve) in the throttle body...since it has such a hard time cold starting and wont idle consistently when warm... And I have no idea what the flashing red battery light was all about...

I'm finding out that this car is a PITA! If I can't get it to start/idle properly, I'm going to install a FIAV delete plate.

 

[Sniffbooger]

I'm returning my new TPS sensor back to the eBay seller. It did not seem to be an authentic Mitsubishi part. There were no DSM diamonds stamped on it or a part number anywhere. However it was advertised and sent packaged in a nice new authentic looking Mitsubishi part bag!

As for performance, the idle switching was not immediate and abrupt as it should be if the throttle is moved only .45 mm.... the continuity between pins three and four existed until I moved the throttle at least a full 1 cm! Resistance at closed throttle measured .047 ohms. I believe it should be closer to zero. And the resistance gradually increased from .047 as I opened the throttle. It was a gradual increase in resistance, not immediate and abrupt as it should be.?...

I could just never get it set correctly with this part. I'm going to order another new one. Anyone have any ideas or thoughts? Does this seem correct? Or am I missing something here...

 

[Sniffbooger]

I sent the faulty TPS back for a refund and ordered a different one. This new one looks like its refurbished, not new. I guess its hard to get what you pay for on ebay these days... anyway, I tested the resistance and functionality of the idle switching circuit which finally operates as it should. Continuity with almost no resistance at closed idle, and very quickly goes to open continuity/ infinite resistance when opening it. Yaay!

So I installed and adjusted until it read .63v at idle, which was near the middle of the adjustment slots, not maxed out clockwise as the last one i sent back. And this one has 4.75v reading at max throttle. Yaay!

I also replaced the old 2g alternator with a new 1g alternator. This was cheaper ($50 compared to $105, both non OEM)....and had to convert 4 wire connector to a 2 wire connector....--thanks to some reading around the forums--...I just crimped some female spades on the two main wires (1 upper red wire for battery and 1 lower black/yellow wire for dummy light). I have a new 2 prong clip with pigtail coming in the mail soon to secure the connection.

After all this, it still has some cold start issues, surging/dying until coolant warms up. I suspect the FIAV is the culprit, probably set open farther than it should be, causing lean mixture and acting like a vacuum leak. Also, there is some shaft play on the cable side of the throttle body. I suspect a minor vacuum leak there. I have another 1g throttle body with good shaft seals I may swap out. That one has a fully screwed shut FIAV so it may eliminate the surging and give me better throttle control for cold starts. I don't mind keeping my foot on the pedal for a couple mins while the engine comes up to temperature. I also ordered a delete plate for the FIAV. That may be what I end up using, just to be sure its sealed.

 

[Sniffbooger]

New 1G alternator is installed and charging between 14.3 and 14.5 volts when running. But now the issue with the alternator is that it has constant power from the battery and doesn't shut off when the key is turned off. So now it drains my battery completely overnight! I think my old 2G alternator with the four wires was controlled by the ECU for power on and off... Now my new 1G alternator seems to be always on and that's a problem....

I also installed the FIAV delete plate on the throttle body. It still starts a little rough when cold but now I can manage to control it with the throttle a little better and keep it from stalling. However, the idle is still a little low and sometimes stalls out when my manual radiator fan is turned on.

Opening the throttle stop screw more doesn't help increase the idle, and also the engine begins to stall after deceleration. Sweet spot seems to be about 3/4 turn in from butterfly bottomed out, where it usually keeps the engine from stalling after deceleration, with no loads on the engine....(but it struggles when there IS a load on the engine). I have a bigger 1g throttle body on a 2g intake. This is probably why I cant open up the throttle stop screw a full 1.25 turns as recommended.


Messing with the BISS screw I can get the rpms up a little, but then the ECU compensates and drops it back down to 500-600 rpms. 272 cams are making a rough, loping idle. Maybe the ECU is having trouble compensating for the bigger cams?

I still need to do boost leak testing. New tester just arrived in the mail today!

 

[Sniffbooger]

Did some boost leak testing and got it idling best I could with the big cams (600 rpms and shaking).. but the ISC stepper motor works as it should....got a new knock sensor, and fixing an oil leak at the turbo drain line, and installing a new WalBro 255 fuel pump soon...and also a fuel pressure regulator...and a new FMIC....it's almost time to install the DSM link!!!