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1G Idle Surge (up & down)

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Blkapache01

Proven Member
76
6
Mar 28, 2017
Birmingham, Alabama
Hey folks,

I need some help. My Talon is reving up and down on the idle and I saw that whenever I hit the sensor on top of the throttle body the speed changes. I included a pic of the sensor in case someone can tell me what it's called.

It's a 2.0 non turbo.
I wanted to include the video but the file is too large.

BTW, I already replaced the mass air flow sensor, new TPS sensor, cleaned throttle body, got a new Idle Air Control Valve and cleaned the EGR valve.
 

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Have you tried plugging that closed throttle sensor back in?, try that first and do you have any vacuum leaks? have you checked?
 
Have you tried plugging that closed throttle sensor back in?, try that first and do you have any vacuum leaks? have you checked?
Hey, yeah, I only left it off to take a clear pic of it. I plugged it back right after I took the photo. I didn't find any leaks. Someone said in another thread that some of these have purge canisters that can leak but I don't know if mine has one. Supposed to be under the passenger side of firewall but I didn't see one.
 
How long have you owned the car? What is the history with the car in regards to recent work done.
Did it used to idle welll?
Check injectors seals, Throttle body shaft seals and biss screw and seal.
Has TB been installed correctly? Meaning throttle plate adjustment, tps adjustment and TPS closed switch. Has all that been set according to factory spec?
Did you have a chance to inspect the FIAV in the TB?
 
The part you reference in the pic is actually the idle position switch. It needs to be adjusted correctly (search) for the car to idle correctly. The idle issue you have is idle surge and is well documented. It's usually a vacuum leak or a BISS screw out of adjustment.
 
Im assuming that you still have the coolant lines going to the throttle body?

Yes, indeed.

How long have you owned the car?
What is the history with the car in regards to recent work done.
Did it used to idle well?
Check injectors seals, Throttle body shaft seals and BISS screw and seal.
Has TB been installed correctly? Meaning throttle plate adjustment, TPS adjustment and TPS closed switch. Has all that been set according to factory spec?

Did you have a chance to inspect the FIAV in the TB?

Well, I've owned it for 25 years, TBH.

I had it sitting up the past 7 years in my garage when the clutch went out and ignored it. Last year, I decided to resurrect it. New clutch, new starter, new timing belt, water pump, engine coolant flush, new head gasket, new piston rings, new idle air control valve, new spark plugs/plug wires, new thermo emissions control valve, fuel injector cleaned and new o-rings, BISS screw o-ring, TPS sensor, Mass Air Flow Sensor, new exhaust manifold, throttle body gasket and cleaned and torqued parts to spec.

Even when it was my daily driver, the idle up and down happened after the first few years I owned it but replacing the IACV worked for a while but came back later.

Now that it's been sitting up, I just wonder what else could be causing it.

The part you reference in the pic is actually the idle position switch. It needs to be adjusted correctly (search) for the car to idle correctly. The idle issue you have is idle surge and is well documented. It's usually a vacuum leak or a BISS screw out of adjustment.

You know, for years I never knew what that part was called. Couldn't find it in my service manual. Have you had to do an adjustment?
 
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And make sure that the throttle body is GROUNDED so that the switch works correctly. It just tells the ECU that the throttle is completely closed, but needs to throw that circuit to ground for it to work. That is what the little metal strap is for on some TB's, to ground it so when the idle switch is closed, it grounds. :)
I have added a ground to mine to make sure it operates correctly.
 
And make sure that the throttle body is GROUNDED so that the switch works correctly. It just tells the ECU that the throttle is completely closed, but needs to throw that circuit to ground for it to work. That is what the little metal strap is for on some TB's, to ground it so when the idle switch is closed, it grounds. :)
I have added a ground to mine to make sure it operates correctly.
Thank you. I'll give that a go.
 
Take a look at your engine temp sensor and connectors. Like an another member mentioned, ensure the coolant lines are still connected to the throttle body.
Has the ECU ever been inspected?

I replaced the ECU with a junkyard part. I made sure the model/ECU numbers matched. There wasn't any change in the performance, though.
 
Idle surging is caused by the engine wanting to idle higher than the coasting idle speed and when the ECU sees that the throttle is closed (via the IPS being grounded) and that the engine RPMs are higher than the programmed RPM's it turns the injectors off until the RPMs drop and then back on to keep the engine from stalling.

The usual cause is idle air bypassing the closed throttle from leaks and misadjustments. Everything that connects to the intake manifold is suspect and given all the things you've touched a general pressure test from the throttle body might be useful to identify sources. Once your sure there are no leaks setting the basic ignition timing and BISS adjustment come next.

On a 1G the IPS also acts as the throttle stop. It limits how far closed the butterfly will go to keep keep blade from jamming in the bore and sets how much air can bleed past. Along with the BISS, FIAV, and ISC control the idle air. The factory service manual cautions against adjusting the IPS normally since it's a critical piece for the TB to work correctly. It then goes on to specify something like 15/16's of a turn after the IPS plunger contacts the throttle pulley.

For those who suggested checking that the IPS was grounding, I'll remind you that the ECU won't attempt decel fuel cut if the IPS doesn't ground the signal when the throttle is closed. So having idle surge is a good indicator that the IPS is working, just pull the wire and see.

The ECU won't attempt to manage the idle speed at all if the IPS isn't telling the ECU that the throttle is closed. That means you also won't see the ECU attempt to raise the idle speed when the Power Steering pump is active, the alternator is creating load, or the AC is on.

Both of your ECUs should be inspected for capacitor leakage and that the ISC drivers are not damaged. Every 1G ECU is plagued by the capacitors leaking over time and must be replaced and any leakage corrected.
 
Any cracks in the air intake tube?
None that I could see or feel. I heard a hiss but it wasn't coming from the air intake tube. Been difficult to track that "phantom" hiss.

Idle surging is caused by the engine wanting to idle higher than the coasting idle speed and when the ECU sees that the throttle is closed (via the IPS being grounded) and that the engine RPMs are higher than the programmed RPM's it turns the injectors off until the RPMs drop and then back on to keep the engine from stalling.

The usual cause is idle air bypassing the closed throttle from leaks and misadjustments. Everything that connects to the intake manifold is suspect and given all the things you've touched a general pressure test from the throttle body might be useful to identify sources. Once your sure there are no leaks setting the basic ignition timing and BISS adjustment come next.

On a 1G the IPS also acts as the throttle stop. It limits how far closed the butterfly will go to keep keep blade from jamming in the bore and sets how much air can bleed past. Along with the BISS, FIAV, and ISC control the idle air. The factory service manual cautions against adjusting the IPS normally since it's a critical piece for the TB to work correctly. It then goes on to specify something like 15/16's of a turn after the IPS plunger contacts the throttle pulley.

For those who suggested checking that the IPS was grounding, I'll remind you that the ECU won't attempt decel fuel cut if the IPS doesn't ground the signal when the throttle is closed. So having idle surge is a good indicator that the IPS is working, just pull the wire and see.

The ECU won't attempt to manage the idle speed at all if the IPS isn't telling the ECU that the throttle is closed. That means you also won't see the ECU attempt to raise the idle speed when the Power Steering pump is active, the alternator is creating load, or the AC is on.

Both of your ECUs should be inspected for capacitor leakage and that the ISC drivers are not damaged. Every 1G ECU is plagued by the capacitors leaking over time and must be replaced and any leakage corrected.

I sold the other ECU on eBay a couple of years ago because it was malfunctioning. Meaning, the CEL wouldn't even light up when key was in the ACC position so I knew it had to be ECU related. I got the same type with same matching model number as my old one from a junkyard and instantly, the CEL was working again, just had the same issue of improper idling. I thought that I read on here that someone used to fix ECUs on this site. Is that still the case and if so, how much to send it off for repair?

The fast idle air valve (fiav) does go bad here and there, if all else checks out I would look for another.

Replaced it with a black/tan part online. No change.

And make sure that the throttle body is GROUNDED so that the switch works correctly. It just tells the ECU that the throttle is completely closed, but needs to throw that circuit to ground for it to work. That is what the little metal strap is for on some TB's, to ground it so when the idle switch is closed, it grounds. :)
I have added a ground to mine to make sure it operates correctly.

How did you ground yours? From what I could tell, with it bolted and the negative wires bolted to the intake, I thought it already was.
 
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There is usually a ground strap that goes thru one of the TB bolts and has a screw on top of the TB that it grounds to. Sometimes those have been tore up and are missing. I just ran a ground to that screw so that the complete TB was grounded for sure.
 
I thought that I read on here that someone used to fix ECUs on this site. Is that still the case and if so, how much to send it off for repair?

I'm sure there are several people on this site that fix ECU's on the side but since I shut down my ECU business 8+ years ago I only recommend using the guys at ECMTuning due to their knowledge, pricing, and after the sale support. They know what to look for and how to correctly fix what they find.
 
I'm sure there are several people on this site that fix ECU's on the side but since I shut down my ECU business 8+ years ago I only recommend using the guys at ECMTuning due to their knowledge, pricing, and after the sale support. They know what to look for and how to correctly fix what they find.

Ahh, man. I got in a tad bit too late...LOL. Thanks for the info, though. I'll look into it. Do you know offhand about how much an ECU repair runs or costs to look at it?

There is usually a ground strap that goes thru one of the TB bolts and has a screw on top of the TB that it grounds to. Sometimes those have been tore up and are missing. I just ran a ground to that screw so that the complete TB was grounded for sure.

Awesome. None of the TB bolts have straps to them so I'm gonna give that a remedy. Thanks.
 
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Here is the thread that has a picture of the ground strap and some info on idle surge also. It may not make any difference but the throttle body is grounded from the factory on 1g's for the idle switch which is why I brought it up to you. In the other thread, you can see that you are not the only one that had no idea the TB was grounded for any reason. :)

http://www.dsmtuners.com/threads/throttle-body-ground-coolant-line-hookup-questions.393540/

Thanks for this info. As "fate would have it" mine does NOT have a ground strap at all. SMH... Do you know where I can get another one or is it ok to create a makeshift strap like a wire and clip on some ring connectors?
 
Just make your own ground and confirm it has continuity to the battery, not just the firewall or such. Then when it "clicks" to ground, the ECU sees that signal and knows you are at idle, or are supposed to be. Make sure the slight bit of slack is in your throttle cable and let the ECU do its work.
Glad to be able to point you to a good thread. :thumb: Thats the whole idea for this "library" in a GREAT forum!

Edit. You can ground to the closest ground point and check for a good ground. I don't go all the way to the battery with a dedicated wire, just ground the TB good so the sensors do their job. :)
Marty

If you find NO GROUND when you check, you may have to adjust the stop switch. It is a simple adjustment but only do it if you can confirm that it ISN'T working correctly. Ask for help if you need to, it's right here!
 
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