Is it the ISC?

[Rgnbull88]

Well I have searched the FAQ and Virtual Mech. did what I could and my 89TSI still is dieing after hard acceleration. I have replaced the fuel pump with the Bosh 350 from TEP, I have replaced the fuel filter, the water temp sensor, the injectors with Trilogy stock replacements, plug wires with Magncore 8mm wires, plugs with NGK Iridiums, and the injector clips. I went to do the TEP reset after putting everything in, as per the FAQ, but I could not get the .90v at the ISC. I am not sure I am even getting the right readings because my wires to the ISC are different colors from the FAQ. They are blk/blu, blk/grn, and blk/red. Tried it several time and I get only .019v to .024v no matter were I put my leeds. The FAQ said something about the wiring harness between the ISC and the ECU being faulty if I don't get the .90v, so what do I need to do to correct it? Any advice would be helpful, Thanks. Edited May 4, 2008 by Rgnbull88

[mikec]

I don't know of any connector on a StarQuest with those wire colors. Are you describing the wire colors on the wires between the ISC itself and the connector or from the main wiring harness to the connector. The FAQ describes wire colors from the harness itself. The wire colors between the ISC (or any part on a Mitsu car actually) and its connector can be any color.

 

The throttle body on 87-later StarQuests will have 7 bundles of wires going to/from it:

* 2-wire bundles to each fuel injector

 

* One 2-wire bundle to a skinny connector on the EGR solenoid control (one of the vacuum+electrical things on the front of the throttle body)

 

* One 2-wire bundle to the secondary air control solenoid (the other vacuum+electrical thing)

 

* One 3-wire bundle to the Throttle Position Sensor (TPS) that's located on the bottom/front of the throttle body; it's a round black thing.

 

* One 3-wire bundle to the Idle Speed Control (ISC) motor itself, this is the round black thing on the BACK/driver side of the t-body. Normally this connector is clipped to the side of the t-body too. Two wires will clearly go to the round black motor; the 3rd wire goes underneath the bracket somewhere... the wiring harness mate to that 3rd wire is the one you need to ground when doing the idle adjustment procedure.

 

* One 3 or 4 wire bundle to the Motor Position Sensor (MPS). The MPS connector is also clipped to the t-body. This is the one that you want the 0.9 volts on... leave the connector plugged into the MPS when you do the voltage test, key ON, engine idling.

 

mike c.

[Rgnbull88]

Yes the wires I described were the ones from the plug to the ISC. I guess I was trying to get the readings from the wrong plug, I will try it tomorrow after work, hopefully will this cure the dieing problem. Thank you mike c. Edited May 6, 2008 by Rgnbull88

[Rgnbull88]

Well after using the right connector, I reset the TPS. The car idles wonderfully, however I am still having the dieing problem. I swapped out the MAS and still the same results. From what I gather from around the site it is the ISC that is the problem. Any one know where I can get one?

[Shelby]

did you test and check the funtion of the noise swt,, it's it's job to telll the ecu that the engine is at idle

also when doing the idle rpm adjust,, did you adjust the min idle screw to just below the normal idle rpm, it should be about 1/2 to 3/4 turn below the normal idle position this helps prevent the rpms from geting too low durring idle resumeing after reving , the min idle screw should in no way interfer with normal idle isc funtions or it will hinder the nose swt funtion

 

you can also have NO airleaks any where , includeing the inj houseing mid houseing seals

Edited May 13, 2008 by Shelby

[Rgnbull88]

did you test and check the funtion of the noise swt,, it's it's job to telll the ecu that the engine is at idle

also when doing the idle rpm adjust,, did you adjust the min idle screw to just below the normal idle rpm, it should be about 1/2 to 3/4 turn below the normal idle position this helps prevent the rpms from geting too low durring idle resumeing after reving , the min idle screw should in no way interfer with normal idle isc funtions or it will hinder the nose swt funtion

 

you can also have NO airleaks any where , includeing the inj houseing mid houseing seals

 

I did check the min idle screw, back the screw out all the way, turned it til the touch point, then backed off 1/2 turn. I was having a tuff time getting the idle to set prior to TPS reset. After I jumpered the yel+red connection to ground, it would idle high then drop about 1 to 2 hundred rpm all of sudden then go back to normal. I believe it was when the fans kicked on. I tried to get it while the fans were off. I was unaware of the nose swt. Is it the switch in the tip of the ISC? If so how would I go abouts testing and checking it? For the air leaks, I sprayed starter fluid almost every were, prior to me changing every thing out, but I will try it again to include the inj housing if the weather calms down for a day. Thanks Shelby.

[Shelby]

testing is easy enought , unplug the ISC connector and with engine off , connect test light to batt neg and probe the 3'd wire on the connector going to the isc, while opening the throddle by hand the test lamp will go off and on if the nose swt is working , lamp on when close'd off when off idle

 

the ISC gets it's instructions from ecu base'd on what the CTS is telling the ecu

 

base idle is set by you,,most find it works best if it's 850 to 950

Edited May 13, 2008 by Shelby

[Rgnbull88]

I tried the test. I'm not sure which is the third wire, I think it's the red one. That is were I started, and I checked them all. I couldn't find my test light so I used my voltmeter. I figured I would see voltage at idle and none off idle. I didn't see any kind of voltage at all, in either position. Though one point I am not totally clear on is, the key would be in the on position with the engine not running to do this, correct? That is how I performed the test. If I did it correctly, then this would mean the nose swt is bad. If so, can this be fixed? One other thing I neglected to mention is when I did a test drive, after the tps reset, the car hesitated or stumbled when I hit the gas, then took off. I am not sure if this has anything to do with my problem, but I figured it may prove helpful in the diagnosis. As for the idle speed I set it at about 900 rpms, though after the tps reset the car wanted to idle at about 1000 to 1100 rpms. When the fans kicked on the rpms would sit at about 900 again. I double check the slack in the throttle cable and it was fine, about 1/4 inch of play.

[Shelby]

you don't need any power at all,,the nose swt is nothing more then a grounding point,, if useing a volt meter,, posi clip to batt posi,, neg lead to wire in the ISC connector (to isc ) move throddle while checking each wire , only one will give any reading at all and that is the nose swt connection wire

if useing test lamp, clip to the batt posi and pointer to the wire,, move throddle lamp lights up if the swt is makeing contact,,open close throddle the lamp goes on and off

if i recall the connector right there are 3 terminals in it,, two are across from each other the odd terminal is to the nose swt ,, " l _ l " _ = nose swt wire

[Rgnbull88]

Gave it a try, and no luck. None of them showed voltage. Suggestions? Edited May 14, 2008 by Rgnbull88

[Shelby]

yes slowly reread post #9

[Rgnbull88]

yes slowly reread post #9

 

Reread the post, tried the test again. I used the voltmeter, hooked the pos leed to the pos terminal and used the neg leed to check the wires. On each wire(leading to the ISC) there was no change. If I am understanding correctly, the nose swt is just a ground point. So, if the nose swt is closed, ie at idle, there would be 12+volts going to ground as if I took the neg leed to any other ground point on the chassie. Or if I used the resistance setting I would get a closed indication (resistance), and if off idle an open. If I am doing this incorrectly please let me know. Maybe I'll just ride down to Autozone and pick up a test light.

[Shelby]

a volt meter will work but theres tons of things that can cause a poor reading on a volt meter,, a test lamp is simple and straight forward , makeing tests for ground swts a lot easier to do and see ,,

your right the nose swt is just a metal piece on the tip of the ISC plunger that makes a ground to the throddle houseing when the throddle is close'd ,, as with any ground , dirt rust , corrosion etc can cause a poor contact ,, a lite is easier and quicker to see

 

page 14-10 in the FSM has a nice cut away of the ISC and the nose swt

[mikec]

To test the nose/idle switch:

 

* Engine is OFF. ISC "motor" connector is totally unplugged.

* Set your test meter to measure OHMs (resistance) on it's least sensitive scale. On analog meters, that's usually the "x1" scale; on digital meters it's usually the "200" scale.

* Connect the meter's black/- lead to the battery "-" post.

* Connect the meter's red/+ lead to the nose/idle switch connector on the connector coming FROM the ISC/nose switch assembly - do NOT connect it to the connector from the main wiring harness.

* With the throttle in the idle position, you should read ZERO ohms. On a digital meter, it should read 0.0 ohms (or something close to zero anyway... under 1.0 ohms). On analog meters, the needle should swing all the way to the right.

* Now open the throttle plates slightly: have a helper push on the gas pedal about half an inch, or reach around the back of the throttle body and turn the linkage a bit... or just push on the exposed throttle cable going into the throttle body assembly. The meter should instantly jump to INFINITE ohms. On a digital meter, it'll show OPEN, nothing at all, dashes, etc - whatever it shows when the meter leads aren't connected to anything. On an analog meter, the needle should swing all the way to the left.

* Release the throttle and make sure the meter goes back to zero ohms. Repeat the last few steps to make sure the switch RELIABLY and CONSISTENTLY responds.

 

Another way to test the idle/nose switch is to leave the ISC/nose switch connector plugged in. Start the engine and let it idle. With the test meter set to DC VOLTS now (not AC... that won't work) hook the black lead to battery "-" again and the red lead to the idle/nose switch wire. You'll read zero volts with the throttle at idle (since the swtich is "shorting" to ground at idle when it works right) and either 5 or 12 volts when you rev the engine a little.

 

For folks not used to using "multimeters" to test volts/ohms, a few basic guidelines:

1: VOLT testing is done with the engine running and the connectors/wires/parts connected normally. The meter leads are "tapped" into the circuit to monitor it. Use the DC volts scales for most tests on cars. The meter will monitor/read the voltage IN THE CIRCUIT; this voltage is provided by something in the circuit - not provided by the meter. Testing voltage is similar to testing vacuum levels on a running engine: you have to "T" into the wiring to get a reading; the guage just shows you "what's in there."

 

2: RESISTANCE (ohms) testing is done with the component being tested OUT of the circuit. That means the wires to/from it, or the connectors, are DISCONNECTED. For parts with only two leads (like temp sensors which have one lead plus the "body" of the sensor screwed into the engine) disconnecting just ONE wire is enough. For multi-wire sensors (like the throttle position sensor) it's better to unplug all wires. The meter leads are connected right to the part being tested. For resistance testing, the meter SUPPLIES THE VOLTAGE needed to test the part. This is like testing vacuum actuated parts: you disconnect the vac hose to the part (e.g. the distributor vacuum advancer) and instead apply your own vacuum source to see what the part does.

 

When testing RESISTANCE, you have to be careful of the voltage injected by your meter; analog meters especially can spit out a fairly high voltage that'll damage the ECU or "active" sensors like the airflow sensor ("active sensor" means parts that have electronic circuitry inside them). Digital meters generally inject lower/safer voltages when doing resistance testing. Also, most analog meters have the injected voltage "backwards" in polarity on the leads: the red lead is negative, the black lead is positive. This backwards polarity can be even more dangerous than the actual voltage; reverse polarity fries many electronic parts instantly. Simple sensors (throttle position sensor, idle/nose switch, the various oil/water temp sensors) won't be damaged by any analog meter. The airflow sensor, ECU, cruise computer, a/c computer, ETACS computer, etc. are far more vulnerable. Unless you know what you're doing, testing those parts with a meter set to RESISTANCE is generally incorrect - and often dangerous to the circuitry.

 

mike c.

[VICE]

Where is the A/C computer located?