2G 2G 4G63 Eclipse GST high idle then reaches temperature and then dies

[Codename_Mitch]

Hey everyone new to the forum, I'm currently having an issue with my '98 GST Coupe it has a high idle from start once it gets up to temperature it starts to come down but still idles at about 1,000 to 1,500 then once it's up to temperature after you drive it around for a little bit if you let off the gas at any point it cuts off and then it has an issue starting up again until it cools down. I've cleaned the TB and MAF sensor, replaced the air filter, and replaced the Air Control Unit as well. This brought the idle down from 3k to 2k on start up.

Should I replace the thermostat?

Thanks in advance for the help, hope the videos give an idea as well

 

[dwb]

Welcome to the forum! Nice to see another DSM in CO. Please do us all a favor and fill out a vehicle profile with your mod list (https://www.dsmtuners.com/dsm-profiles/)

Have you checked for any diagnostic/check engine light codes? Do you have anyway to log the car (i.e. ECMLink)? If not I'd start by looking at and/or replacing the coolant temp sensor. Thermostat is only relevant if you are overheating.

 

[jcastello214]

Check and make sure your throttle shaft seals aren't leaking..id just do a boost leak test to verify everything is sealed properly.

 

[We're on Boost]

replaced the Air Control Unit as well

What is the Air Control Unit? Are you talking about Air Conditioning?

Have you replaced the ISC? (idle speed control)(also called IAC, idle air control)
It's a little stepper motor valve thingie.

 

[Codename_Mitch]

Welcome to the forum! Nice to see another DSM in CO. Please do us all a favor and fill out a vehicle profile with your mod list (https://www.dsmtuners.com/dsm-profiles/)

Have you checked for any diagnostic/check engine light codes? Do you have anyway to log the car (i.e. ECMLink)? If not I'd start by looking at and/or replacing the coolant temp sensor. Thermostat is only relevant if you are overheating.

There isn't any CEL showing I plugged in my OBD reader and nothing popped up, I was looking into the ECM link but don't know if it's complicated or not to run. I definitely haven't replaced that sensor yet so I'll give that a shot, I was also told that It might be a vacuum leak from the EGR and I should add a block off plate. Pros vs cons?

 

[Codename_Mitch]

Check and make sure your throttle shaft seals aren't leaking..id just do a boost leak test to verify everything is sealed properly.

I ordered all new silicone hoses and new clamps just waiting on them to arrive and then I was going to run a boost leak test should I just do the test before hand?

 

[Codename_Mitch]

What is the Air Control Unit? Are you talking about Air Conditioning?

Have you replaced the ISC? (idle speed control)(also called IAC, idle air control)
It's a little stepper motor valve thingie.

Yes I replaced the ISC, sorry for the mix up. That dropped the idle RPfrom 3k to 2k on start up.

 

[Justin DuBois]

Yes I replaced the ISC, sorry for the mix up. That dropped the idle RPfrom 3k to 2k on start up.

Cold start with a functioning FIAV is 2000, then as the coolant come to temp, the FIAV closes off some air. what is the condition of your Fast Idle Air Valve? is coolant plumbed to the Throttle Body?

 

[Codename_Mitch]

Cold start with a functioning FIAV is 2000, then as the coolant come to temp, the FIAV closes off some air. what is the condition of your Fast Idle Air Valve? is coolant plumbed to the Throttle Body?

I replaced the Idle Air Valve. Just today didn't seem to change anything. I replaced the Coolant temperature Sensor and now it's showing temps are around 250F at idle. The vehicle still hauts off after running for abit. I replaced the spark plugs, as well. Would the fuel filter/ fuel pump be an issue for start up and to.keep it running?

 

[Justin DuBois]

I replaced the Idle Air Valve. Just today didn't seem to change anything. I replaced the Coolant temperature Sensor and now it's showing temps are around 250F at idle. The vehicle still hauts off after running for abit. I replaced the spark plugs, as well. Would the fuel filter/ fuel pump be an issue for start up and to.keep it running?

IAC is an active stepper motor idle control valve.
FIAV is different. Its bolted to the bottom of the Throttle body, and has coolant lines plumbed to it.

Temp sensor is wrong - nothing will work right without correct coolant values. As a diagnostic test you can force ecmlink to ignore the coolant temp. There is a checkbox in the ecu inputs tab

 

[Codename_Mitch]

IAC is an active stepper motor idle control valve.
FIAV is different. Its bolted to the bottom of the Throttle body, and has coolant lines plumbed to it.

Temp sensor is wrong - nothing will work right without correct coolant values. As a diagnostic test you can force ecmlink to ignore the coolant temp. There is a checkbox in the ecu inputs tab

I'll check the FIAV when I get back to it on Monday.
I've been reading about a delete for it is that necessary or just an option?

Also thank you for all of your help

 

[Justin DuBois]

I'll check the FIAV when I get back to it on Monday.
I've been reading about a delete for it is that necessary or just an option?

Also thank you for all of your help

The delete is only better when the valve is broken (leaking coolant or air) Deleting the FIAV comes with side effects, mostly you have to hold the throttle open in order to get the engine to start, and hold it open 1-2 min until the coolant temps come up to 140. Its better to have a working FIAV hooked to coolant lines.

 

[We're on Boost]

I replaced the Coolant temperature Sensor and now it's showing temps are around 250F at idle.

Just want to clarify this a little. You don't have ECMlink, so the 250 deg F number you get for temp is coming from a Glow Shift gauge, I guess, right?
The coolant temp sensor you replaced is not for the Glow Shift, it is the one the car's ecu uses, right?
The car's coolant temp sensors, if it is like 1g, there are 2 of them. One that the ecu uses, the other one is used by the vague temp gauge in the stock instrument cluster.
Could you give us a link to the exact coolant temp sensor you bought for this - need to check the make and part number of the sensor.
Another thing to check is the condition of the wires right where they go into the electrical plug on the coolant temp sensor. Could you take a pic of the sensor showing the wires there, and post it. Usually the wires get frayed there, or the plug could be broken.

 

[Codename_Mitch]

Just want to clarify this a little. You don't have ECMlink, so the 250 deg F number you get for temp is coming from a Glow Shift gauge, I guess, right?
The coolant temp sensor you replaced is not for the Glow Shift, it is the one the car's ecu uses, right?
The car's coolant temp sensors, if it is like 1g, there are 2 of them. One that the ecu uses, the other one is used by the vague temp gauge in the stock instrument cluster.
Could you give us a link to the exact coolant temp sensor you bought for this - need to check the make and part number of the sensor.
Another thing to check is the condition of the wires right where they go into the electrical plug on the coolant temp sensor. Could you take a pic of the sensor showing the wires there, and post it. Usually the wires get frayed there, or the plug could be broken.

Yes the number is coming From the glow gauge, I purchased the vehicle like this. And so I know only so much about what was done with it. The one I purchased was from AutoZone. I'll try to find the link for it here. It was the sensor and not the sender that I replaced so would that make a difference ?

The plug and wires are all in good shape as they were replaced before I purchased the vehicle.

Update: I replaced the TB and added the FIAV block plate. The vehicle starts right up and idles at 1500.
I drove it around today and when the temp on the gauge got up to 220 and I let off the gas it would die and doesn't start up again which has been the main problem

 

[We're on Boost]

The one I purchased was from AutoZone. I'll try to find the link for it here. It was the sensor and not the sender that I replaced so would that make a difference ?

Sensor is probably what it's usually called rather than sender. AutoZone has one that looks correct for 1998 GST and I have it bookmarked, just want to make sure that's the one you got.

I replaced the TB and added the FIAV block plate.

Oops gotta check on this too because "block" is the wrong word.
You would want a "Bypass" plate rather than a "Block off" plate, for the the FIAV delete.
FIAV Bypass Plate - 91-99 DSM
FIAV Block Off Plate for 91-99 DSM

 

[Codename_Mitch]

So it was actually advanced Auto gets the link https://shop.advanceautoparts.com/p...re=1089&searchTerm=coolant+temperature+sensor

And I can confirm that I did get the bypass plate

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[We're on Boost]

So it was actually advanced Auto gets the link https://shop.advanceautoparts.com/p...re=1089&searchTerm=coolant+temperature+sensor

And I can confirm that I did get the bypass plate

Ok, bypass plate is good.
The sensor is probably ok. If you want, we could check the resistance (ohms) of it with a multimeter if you have one. It would be simple to check it when the engine is cool. A little more annoying to do it when the engine is warm. But the best check is to do it at 2 different temps. This is something you can do with this type of sensor even if it's not even in the car at all. The idea is that its resistance decreases as it gets warmer, and we have some numbers for what the resistance should be at 2 or 3 different temps.
The actual trouble is probably something else entirely since these 2 changes didn't seem to help.

 

[Codename_Mitch]

I have a multimeter so I can do a check on it and see what the numbers come out at.

Would it be possible it could be an issue with the fuel? Maybe the filter or pump?

 

[We're on Boost]

I have a multimeter so I can do a check on it and see what the numbers come out at.

Would it be possible it could be an issue with the fuel? Maybe the filter or pump?

We're probably going to need some help from some 2g people. I'm going to be gone for the next 3 days anyway and am kind of on my way out right now.

To check the sensor with a meter, just take the electrical plug off the sensor so that the 2 pins are exposed, and measure ohms between the 2 pins. Try to get numbers for it at 2 different temps.

The 250 degrees is a little weird. Your fan should come on well before that. Does the fan come on at all? What temp does your gauge say when the fan comes on?

We might need to look inside your ecu at some point. Could start just by finding out where it is located. Sometimes there is a problem on the circuit board that is visible in a good photo.

Does the car have air conditioning?

The Mishimoto fans, are there 2 of them?

I wouldn't think that a fuel system problem would show up only when hot like yours is doing.

You mentioned EGR blockoff earlier as a possible thing to do. When I had the stock parts there I put an EGR block off plate on it. I don't think there was any downside to it, but I don't even remember why I did it or if there were any other things that had to be done to go with it .

 

[We're on Boost]

On the 250 degrees again, there was a 2g in here a couple years ago where they found cracks in the underside of the exhaust manifold. It had been causing them a lot of trouble. Anyway, take a look at their pics. Try to see that area on your manifold.