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ISC? TPS? IDFK?!
Topic Started: Sep 14 2013, 01:58 AM (1,775 Views)
compjake
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When my car is cold I'll start her up and she will gladly idle at a nice smooth 800 rpms, problem is once its at normal operating temperature it will idle at about 1300 rpms.. So basicly the cold start function works but in the opposite manner it should. I don't have a surging idle so I THINK the ISC is working fine, and no matter where I set the TPS it doesn't change anything except make a 2000 rpm idle when hot.

How do I fix this stupid thing? I can't enjoy my new engine when the damn thing wont idle correctly :banghead
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clarkdw


Almost sounds like your ISC isn't working at all. It should idle higher than 800 cold. Any DTC codes? Engine light on? Does the check engine light come on when you turn the key on before starting it?

Can you see the ISC move when you turn the key on and start the car?

Edited by clarkdw, Sep 14 2013, 02:51 AM.
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compjake
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I know, it should be at the 1200-1300 range I believe. No codes, and no CEL. CEL was on when my IAT wasn't working but I changed the broken plug and that's working fine now. I plan to reset my TPS with my DMM tomorrow afternoon, I normally just set it by ear clearly that's not an accurate way to do it lol

Yes, If I have KOEO the ISC will hum a couple times and stop, if I push on the plunger with my finger it will go in slowly, as the solenoid allows. It then just resets at that position until I stop pushing on it. After doing this the idle when hot is around 800 rpm, but over the next 30-45 seconds the idle will slowly go back up to 12-1300 rpm.

If I set the TPS as far as you can turn it clockwise the ISC will change the idle up to about 2000 rpm cold or hot doesn't matter, any other setting on the TPS results in this issue. :banghead
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clarkdw


Do you have a Factory Service Manual? If not then there is a 94 FSM in the manuals section of the forum. If you go to section 6E2-A2 it is the troubleshooting section of the upgraded emissions. That is exactly the same as your car. As long as the section of the manual applies to upgraded emissions it will cover your car.

Possible bad ground onthe ECT? Check both grounds on the back of the intake manifold.

ECT will cause high idle when warm if it tells the ECM that the engine is not warming up but that doesn't explain the low idle when cold.

I have a feeling that you may have a sticky ISC.

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compjake
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I don't, I looked around couldn't find it. Can you link me please? and finally found it :)

I doubt a bad ground, but I will check them. Engine has only been in the car for about 3000 miles lol
Edited by compjake, Sep 14 2013, 07:04 AM.
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Memphis metro


Will your car warm up to normal operating temperature? What is the timing set at?
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clarkdw


The reason I suspect the ISC as opposed to temp related problem is that the symptom of low idle when cold should not occur if the ECT is giving a low temp signal to the ECM. The low temp idle should be normal. If the engine wasn't warming up the symptom should only be a high idle all the time.

You have low idle when cold and high idle when warm. That is a pretty good indication of an ISC that is making no adjustments at all.
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compjake
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It would appear my issue was the idle set screw. I unscrewed it most the way, pushed the ISC plunger in all the way then screwed the idle set screw in just far enough that the butterfly valve wouldn't stick. Set TPS by feel with KOEO (Adjust TPS until there is about 1.2mm gap between throttle linkage and ISC plunger) Tighten screws on TPS, put air cleaner back on, reconnect IAT sensor and done. It idles at 1000 rpm cold and 800 hot.

No wonder JM and everyone else says to never touch that screw, it makes you think your TPS and ISC don't work lol
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clarkdw


:thumb Glad you found that. I had the same issue. P.O. had messed with the setting of the throttle stop screw and you can never get the engine to idle properly without setting it back to the correct spot.
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compjake
Sep 14 2013, 06:29 PM
No wonder JM and everyone else says to never touch that screw, it makes you think your TPS and ISC don't work lol
:lol Normally, when someone messes with the TPS or throttle stop screw, Guido pays a little visit to remove a couple of your fingers at the second knuckle. In this case, since you fixed it, you have been spared. ^o)


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compjake
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Well a lot of good that all did. Everything was fine with my idle and all of a sudden today it cold idles at like 300 rpms and hot idles at 1200 again.
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clarkdw


Set your TPS according to the instructions here for the upgraded emissions. I use a 9/64" allen key as the spacer. It is 0.140 inches.

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Edited by clarkdw, Sep 15 2013, 06:45 PM.
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clarkdw


I guess that isn't too clear if you don't have a Tech1. Follow the instructions but use your DMM and measure from pin 3 to the battery negative or your manifold ground.

KOEO on your TPS you should have 5v on pin 1. Pin 2 is open. Pin 3 should vary from 0v-4v give or take. Pin 4 should be grounded. Obviously this is with the connector still plugged in.
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compjake
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The image doesn't load. I'll give that a go, I had planned to originally.
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2000Firefly1.3L
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compjake
Sep 14 2013, 06:29 PM
It would appear my issue was the idle set screw. I unscrewed it most the way, pushed the ISC plunger in all the way then screwed the idle set screw in just far enough that the butterfly valve wouldn't stick. Set TPS by feel with KOEO (Adjust TPS until there is about 1.2mm gap between throttle linkage and ISC plunger) Tighten screws on TPS, put air cleaner back on, reconnect IAT sensor and done. It idles at 1000 rpm cold and 800 hot.

No wonder JM and everyone else says to never touch that screw, it makes you think your TPS and ISC don't work lol
hrm, i decided to give this a shot. as it were, my idle screw adjust was out by a little. a clockwise turn to increase the throttle plate opening just slightly managed to remedy the hunting idle speed with A/C on. 8mm bolt and 2.5mm allen screw. i did this with the engine running to experiment with the proper setting, checking the A/C on and off as well as other accessories and throttle play. just tuned it by ear and the ISC motor now keeps the idle between 750 and 850 as it should be.
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