ISC Valve replacement.

87CandyBlueT

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I bought an ISC valve on ebay and replaced it and the car ran terrible so i put the old one back on and it runs a little better but I can't get the idle right it's way to fast and the car is very jerky when shifting. Any suggestions or help would be greatly appreciated. Thanks
 

shaeff

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is either one of them clicking after you shut off the motor? like this:

click click, click click, click click.

-shaeff
 

supraman7mgte

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idles too fast? that might not be the culprit. in my experience,a bad ISC will make the rpm's drop to about 750. have you looked up the prob in the TRSM
Derp,normal idle is around 650
 
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87CandyBlueT

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Yes it does click. I didn't replace the diaphram or seal I didn't have them to replace. Also it was doing an idle surge problem is why I changed the ISC. Now after changing I can't get it to idle slower and it jerks when shifting and feels like it's pulling to much like the idle is to highor low when shifting. Downshifts don't slow me down as much etc.
 

87CandyBlueT

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87CandyBlueT said:
Yes it does click. I didn't replace the diaphram or seal I didn't have them to replace. Also it was doing an idle surge problem is why I changed the ISC. Now after changing I can't get it to idle slower and it jerks when shifting and feels like it's pulling to much like the idle is to highor low when shifting. Downshifts don't slow me down as much etc.
 

toml

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Sorry, but just so I am clear after reading that very informative post from jetjock... if the engine clicks after shutting off, it means the ISC valve is returning to full open and is a good thing? :)

Thanks.
 

jetjock

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toml said:
Sorry, but just so I am clear after reading that very informative post from jetjock... if the engine clicks after shutting off, it means the ISC valve is returning to full open and is a good thing? :)Thanks.

Well, if the ISC valve clicks then yes, give the man a cigar ;).

The ISC valve has no "positional feedback" ie, whenever the ECU tells it to step X number of steps it assumes it actually moved but has no way of verifying it. While it's true the ISC system is a closed feedback loop, it's closed only in that a devitaion from targeted idle speed is sensed by engine rpm and corrected. The ISC valve itself is open loop in the sense it has no way to "report back" it's done what the ECU told it to do.

Since the ISC valve can't report back it's actual position the ECU could lose track of it's position on shutdown. Therefore the ECU needs to put the valve someplace so the ECU can start from scratch. In fact, the TCCS initializes a whole bunch of things every time you turn the key. This is called "housekeeping" in automation engineering. It's needed to "reset" output devices in open loops to a predetermined position prior to putting them into operation.

The valve position could be reset on start up but that would cause a delay getting right on the target idle the ECU wants, so Toyota does it by stepping the valve 125 steps back (to full open) after engine shutdown and putting that position in memory. Got it? Probably a lot more than you wanted to know but it's basic control theory when designing closed loop systems that don't employ positional feedback.
 
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87CandyBlueT

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Well after i changed out the ISC valve the second time using my original ISC valve. On the way home right after the engine light came on for about 20 minutes. Now I read somewhere about getting the engine diagnostic codes. Does anyone know in detail how to do this and to see what each code is? I try holding in the far left button and the (M)minute button. It pops up error and then DIAG but goes no further. Thanks, no I had no ISC valve gasket or anything just the piece itself. (I cleaned the ISC valve with carb. cleaner before installing. The auto parts store said they couldn't find the gasket to even order it.
 

figgie

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jetjock said:
There isn't much that can go wrong with that thing and I suspect many get changed for no reason. It's nothing more than a 4 pole stepper with a total movement of 125 steps. I'm betting your problm lies elsewhere but here's some tech details about the ICS system. On the 7M idle control is based on the following inputs. Some targeted idle speeds are variable while others are fixed.:

1) Engine speed (NE)

2) TPS: ISC is only active when IDL contacts on the TPS are closed. A quick check of the IDL contacts can be done by shorting E1 and T with the engine off and opening the throttle slighty. The code for IDL should be displayed (I forget what it is).

3) Coolant Temp (THW)....for cold idle.

4) Vehicle speed (SPD): While the ECU could simply look at the IDL contacts on the TPS there are obviously cases where the vehicle is moving with the throttle closed. For example, you wouldn't want cold idle active while braking to a stop.

5) Air conditoner clutch (AC): For idle up when the A/C is on.

6) Headlight operation: On the Supra the headlight switch sends a signal to the ELS (electrical load) terminal on the ECU. Other alternator loads are sensed by engine speed. This setup is different from most Toyotas but it works out OK.

7) Battery voltage: The ECU looks at B+ for several reasons anyway.

There are a few other inputs monitored for cars with auto trannies and the inputs mentioned are used together in some cases. For example, for cold idle the ECU looks at coolant temp, engine speed, checks that the IDL contacts on the TPS are closed and vehicle speed is zero. Needless to say engine speed is always being sampled as it's the primary process variable (what needs to be controlled) in the loop. After all, how can idle be controlled if the ECU doesn't know what the engine speed is in the first place?

Other than a winding opening up the only other failure modes are the bearings or gunking of the screw nut or screw itself. ISC valves can be easily tested as per the service manual. As shaeff pointed out, a quick electrical check is to listen for the ISC valve stepping back to full open just after the engine is shut down. That doesn't mean the pintle is actually moving however. Also keep in mind the Supra's ISC system is "smart" in that the values used are periodically re-written in the ECU's memory.

If the ISC valve fails it'll remain at it's last controlled position. This makes sense but needs to be pointed out as it will obviously effect the amount of air bypassing the TB under all conditions. On turbo cars there is a check valve on the manifold side of the ISC valve. It needs to flow air in one direction but stop boost in the other.

Lastly, it's important to remember the ECU uses inputs for multiple tasks. Obviously the coolant temp is used for more than idle speed control. This is why it's painful to read about busted sensors or bad wiring. If you want the car to run right you need to be sure that all sensors and wiring associated with the TCCS are in good condition. Even then a sensor can be out of whack and not throw a code. The MKIII's OBD-I system isn't very bright when it comes to this, it's much dumber than OBD-II.


toyota actually uses a 6 pole stepper and more specifically the stepper is a unipolar design. If it was a 4 pole stepper it could only be a bipolar stepper. Toyota states (from the autoshop101 site) the stepper motor has 125 steps. Reality it actually has 255 steps as i had it tested to see if it was compatabile with standalone and infact it is and at that time it was revealed to me the amount of steps the ISC has :)

In all my years working with stepper motors and the supra. I have yet to see one take a crap without giving issues beforehand. the ones that have died didn't click or where always runing at x rpm without change.
 

87CandyBlueT

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When the vehicle is warmed up the lowest I can get it to idle is 1300 RPM. My idle screw on the TB is all the way to the right, the lowest it can go. It seems like their is something wrong with my throttle too. I adjusted the stop screw some but still no dice.
 

shaeff

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seriously. i was going to answer the questions that came after my previous post, but it's all learning right now! :)

-shaeff
 

87CandyBlueT

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Also I noticed this noise when i accelerate. Like chattering/ticking noise. I assume the valves. Anyway since this high idle and jerking problem the chattering has gotten louder. Anyone can point me in the right direction would be great.
 

figgie

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yeah

I did a lot of digging into the ISC just because everyone was saying that the stock ISC can not be ran by a standalone and boy where they all wrong, lmao.

If the standalone can drive a a 4 wire GM based stepper motor it can drive the Toyota ISC valve. :)