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Unstable idle help. Oldskoolers and troubleshooters PLS.

misterfixit

Well-known member
Joined
Aug 4, 2004
Messages
1,583
Location
Midlands, UK
Hi All.

My freind here has a 92 Galant DOHC. It has some idle issues. Unfortunately my crates full of galant stuff are back home. I however did bring my logger.

When the car is turned on the idle goes to about 2500 then sinks to an oscillation from 1,200 to about 2000. Sounds like the ecu but please read the following.

1, all connections in the engine bay are good.
2, idle switch functioning and set correctly
3, TPS set using the logger correctly
4, CAS is good

The ECU was capped by me about 9 moths ago and there was no damage on the board.
ECU communicates with the logger. There are sensible redings coming out of all sensors except the ISC. That is flatlined at 0 on the logger. But MMCD shows no error codes in the ECU memory.

I tried a Hyundai ecu I brought over from the UK, that runs, but again the car suffers from a high idle. ISC readings fluctuate on theat one. The servo is good, but here's where the questions start to formulate in my head. It looks a little different than I'm used to seeing a rim around the outer face, this is a smaller thing. Masuring the depth of the bore vs the height of the servo with a vernier looks to be ok. PN MD628051 Is that OK? It's not listed in the Jap parts book I have here.

I popped the ecu apart and traced and belled out the traces back to the ISC drivers and these are all good (all4)(def no cap damage) so I'm a little stuck. This is for both ECU's

One last thing. No knock sensor. No lambda sensor, only basic emissions kit as std equipment here.

Can anyone help with some ideas?

Cheers,

Rich
 

Noobsauce

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Joined
Apr 7, 2012
Messages
159
Location
Beaverton, Oregon
What are the resistance readings on the isc?
Testing the wiring harness. what are the resistance readings from the isc to the ECU?
 
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cheekychimp

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Joined
Apr 19, 2004
Messages
7,333
Location
East Sussex, U.K.
Rich,
When I was having idle issues I bought two brand new ISC motors from the States. There was nothing to suggest from anyone that I spoke to or in CAPS that these wouldn't work in a JDM car but they didn't. The length was wrong so that no matter how the ISC tried to compensate it couldn't reduce the airflow enough to get under 2000 rpm. You might want to try another ISC.
 
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matt92vr4

Well-known member
Joined
Oct 3, 2010
Messages
676
Location
Venice, FL
Most surging idle issues I've dealt with were caused from an air leak somewhere after the MAF. Either pressure test or squirt some starting fluid around the intake pipes and throttle body while the car is running to see if you can find the leak. The leak will suck in the starting fluid and surge the engine.
 

misterfixit

Well-known member
Joined
Aug 4, 2004
Messages
1,583
Location
Midlands, UK
I will do some more research and try to test the ecu and maf on a known good car.

I would be inclined to agree on the airleak, but to get a 1.5 to 2 increase then acually be seeing the isc doing nothing to compensate on the logger i think thats one to discount.

I'll test the MAF because it's an easy double check, but i'm seeing sensible readings on frequency (hz) and the other attributes.

Paul, i seem to remember when you were having ISC issues. Can you remember the thread? When my head feels less like it's about to fall off I'll have a good search and see what I Can dig up.

Cheers

Rich
 

brisvr4

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Feb 13, 2004
Messages
955
Location
brisbane australia
Check the fiav too. It will cause this exact condition.
 

misterfixit

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Joined
Aug 4, 2004
Messages
1,583
Location
Midlands, UK
Thats also on the list, when the car got here yesterday the coolant was 108c and i didn't want to tear the t/body off witout a gasket.

It's amazing how painful it is holding screws you've just pulled out of a hot engine to pull the isc out. them suckers were hot.... ! /ubbthreads/images/graemlins/frown.gif

Rich
 

cheekychimp

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Apr 19, 2004
Messages
7,333
Location
East Sussex, U.K.
Quoting misterfixit:


Paul, i seem to remember when you were having ISC issues. Can you remember the thread? When my head feels less like it's about to fall off I'll have a good search and see what I Can dig up.

Cheers

Rich



Rich,

This was my thread click which I updated in the last post to include everything that we did to solve my issues.

I'm convinced that my poor idle was a combination of a number of issues, not least of which was a faulty power steering sensor (hence the constant stalling in the car park at very low speeds). However about half way down you can see minor references to the new DSM ISC that I fitted which simply would not work. Idle was stuck at 1500 rpms or thereabouts!

I have yet to find any info that proves USDM throttle bodies are different to JDM ones BUT both my cars are 1990 models. It may be possible that JDM 1990 throttle bodies are different to the 1991-1992 throttle bodies that USDM cars have. That would make sense since when I fitted my S90 aftermarket throttle body the FIAV/ISC assembly from the 1990 throttle body was not a straight bolt up whereas the Aussie Boys on here advised me that their 1991 and above assemblies bolted up just fine.

I am leaning towards the idea that there is a slight difference between the earlier throttle bodies and later ones and that consequently you DO need the correct ISC to get a smooth idle. However without any documentary proof I am loathe to make that statement. If I had my two new ISCs to hand I would have dug them out and posted up the part no. so that you could compare it with what you have there. Unfortunately I am moving house right now and have so many boxes I can't even find my spare ECU that Ken wanted to borrow never mind something as easily lost in a box as an ISC. However if you go to www.dsmisc.com there is a pic of the ISC they sent me on the front page (on the right) that you can compare with the one you have.

Everyone tells me the USDM ISC should work, but it won't, not in my idle control assembly anyway. What I most likely will do at some point is buy a 1991-1992 USDM throttle body (or just the idle assembly) and have it cleaned up/reconditioned to see if that works with the new ISCs. But for the moment whilst everything is working just fine I am sticking with the "if it ain't broke don't fix it" policy!
 
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JNR

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Joined
Apr 23, 2004
Messages
9,803
Location
ca
How's the vacuum look? Not just the #, but how it behaves...don't use a boost gauge for that, but a real vacuum gauge and that will tell you a lot (too lazy to pull the links up, but do a search online /ubbthreads/images/graemlins/smile.gif )
 

misterfixit

Well-known member
Joined
Aug 4, 2004
Messages
1,583
Location
Midlands, UK
Looked through the system and it's showing OK. I'm still with Paul on the ISC thing.

Found this service news letter:



4G6 is listed as MD628051, but the original 1993 jap parts catalogue says MD614367=>MD628052 Which oddly is listed against 4G9...
Both the new and the installed servo did the same thing and looked exactly the same.

Can anyone help and supply some hpotos of known ISC's in this thread (not the chinabay alibaba sh*t google throws up) but actual parts we the community have kicking around.
Need:
MD614367/e9t15293
MD628052/e9t15293c
MD614368/e9t15292
MD628051/e9t15292c

All help muchly appreciated.

Paul how can you loose an ISC in a house move? It should be in the same box as thekettle and the teabags!! /ubbthreads/images/graemlins/rofl.gif

Cheers again

Rich
 

misterfixit

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Joined
Aug 4, 2004
Messages
1,583
Location
Midlands, UK
Todays progress and chaps I need some input here.

"Mitz" is back at my house, she's here for a few days so I've removed the throttle body. As that's the biggest issue in my head right now.

I figure high idle is because of a big air leak or excessive air from somewhere. The ECU is actively trying to bring the idle down by driving the ISC to 0.
Secondly as well as hunting it's in the 2.5K range with the idle screw wound shut.

This leaves 3 sources of leak past the throttle to cause an over 1.5K increase and it to be well outside the range of control of the ecu.
i, The throttle is not shut.
ii, The ISC is not shutting enough
iii, The FIAV is too open.

I Cannot upload pictures tonight despite trying for over an hour... /ubbthreads/images/graemlins/frown.gif

I have stripped the FIAV and would like some help determining two things.
1, How open is the orifice supposed to be when cold?
2, The brass T/stat leg in the rear of the FIAV. is the little leg supposed to stick out when cold and if so how much?

When going over the Tbody, I also noticed some other things.
A, The throttle valve was not completely closed on the idle switch. When held to the light there was a 0.5mm Halo around the butterfly.
B, when stripping and manually extending the ISC while mounted on the Idle control block it closes the orifice but doesn't seal completely. Is this normal? I tested using Carb cleaner and there was a slow but pronounced leak.
C, The throttle stop screw is wound in tight even with this it's sitting at 2.5K
D, After knocking the plug out over the FIAV the plug is about 4-5mm downin the centre at cold. Consequently the anulus around it is huge. What is the correct depth from rim to plug when cold?
E, Pulling that apart and looking at the thermo leg underneath it would appear that the central stick is bottomed (flush with the top of it's housing) Should it be?

Gut feel after tearing the whpole lot down is the throttle butterfly and the FIAV are the biggest culprits. I think i'm satisfied after the dousing and experimenting tonight the ISC has enough authority over it's port.

So to Brisvr4 thanks! i think I'm now chasing out your theory now I have the beast here and torn down.

Rich
 
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misterfixit

Well-known member
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Aug 4, 2004
Messages
1,583
Location
Midlands, UK
There will be no leak from boost. Its an NA 4G63. The Only places there could be a leak are at the t/body. The manifold to head, or the rubber intake pipe.

Rich
 

Noobsauce

Well-known member
Joined
Apr 7, 2012
Messages
159
Location
Beaverton, Oregon
Then it will be even Easyer to find the leak. Hook it to the throttle body flange.
Or you can use a smoke tester and install it to one of the ports to the maf inlet tube. Remove the maf and plug the hole.
 
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misterfixit

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Joined
Aug 4, 2004
Messages
1,583
Location
Midlands, UK
FIXED!!!!!! /ubbthreads/images/graemlins/smile.gif

Noobscauce you were right it was an epic leak. However not anywhere else other than the throttlebody.

The FIAV was the culprit. I have completely rebuilt it and reset it. I had to improvise a method which I will outline. When I have a little more time I'll do a how-to on it.

'MITZ' has now gone home and is idling smoothly warm and cold /ubbthreads/images/graemlins/wink.gif

The FIAV is responsible for lifting the idle 200rpm when the engine is clack cold. It should shut off completely when the water gets to 50-60c.
I dinked the bare FIAV in a pan of water and put the ring on to see how much actuation travel and how much force there was. I kept check on it using a houshold thermometer. In the case of this FIAV it moved about 2mm and no more up to boiling. The plunger was quite stiff, but not so stiff it would not have a balancing effect from the FIAV spring.

Next I cooled it down and reassembled the FIAV, but with no cap. I adjusted it to appx 1mm off the stop. The whole lot went back in the pan (with fresh water) and I started the process again. After a little bit at 55c I took it out and tried to blow throught the valve. I adjusted the gland (screwy seat thing) until it just bottomed at the 55c.

Next I stuck cold water (under the tap) into the water feed to take the heat away. valve was now opened but wet! /ubbthreads/images/graemlins/wink.gif.
I used a depth mic to measure the gland to the front face of the body and marked the gland for orientation 1turn is about 0.5mm or just a tadge more.

I took the whole lot apart again and cleaned and dried it all. When dry I smeared a thin film of sealant around the outside of the gland and reassembled back to the measured and marked position. Interestingly on the body there was evidence of some thread locking paste or something much further down the thread from where I discovered the gland.

I replaced the rear cap using a close fitting socket and a smear of sealant for good measure (Idid knock the cap out originally) and reassembled the body.
I double checked the idle switch and TPS. the servo I was more than happy with and put it back on the car.

Car fired lovely and immidiately died. OOPs, I'd left the idle screw tight shut. Backed it out three turns to see where we'd be at and she ran smooth at 1100rpm.

Got the logger out and fiddled with the idle when she was warm to give an ISC around the 25 mark (idle screw only gave authority from 0 to 55 FSD) and she was happily purring away at 850 when she was warm.

On the run back home she was, strong smooth and well mannered. Owner was chuffed to bits with the result, as was I

Cheers for all the input guys! Another truly global effort!

Rich
 
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