Idle surge that fixes itself

[Dawson159]

I have a 98 Eclipse gst with 127k miles that has really weird idle surge
When u start the car will idle surge Minorly not bad and will do it for a while and randomly spike up to 2k rpms then settle at around 1k rpms where it’s supposed to be (depending on how cold it is outside) but if u tried to drive it before the idle spiked and settled it would get to 2k rpms and sputter and jerk until u hit boost then it would slingshot u forward then would surge really bad if u came to a stoplight between 300-800 rpms which made it pretty much undrivable.
I researched it and thought it was the tps so I replaced it and started the car and it didn’t surge at start or anything so I thought it was fixed so I went to drive it and it was fine until I Parked at target then started it up again and it was back to Surging again so I drove it to see if it would jerk and sputter and it did but only half as bad (almost unnoticeably) but then when I came to a stop light it would idle surge REALLY bad just like before I replaced the tps do idk what’s wrong I’ve replaced the iac, the tps, and bypassed the fiav, and blocked the egr.

I don’t know what else it could be the weirdest part is that it fixes itself after about 3 minutes of idle then it drives perfectly fine. I really thought it was gonna be the tps unless I installed something wrong.. it was a used tps btw

What do U guys think? Thanks in advance

 

[chrysler kid]

It sounds like typical symptoms of bypassing the fiav. Hook it back up

 

[Dawson159]

It sounds like typical symptoms of bypassing the fiav. Hook it back up

Well damn I bypassed it to stop idle surge and it’s idle surging because its bypassed now what do I do?

 

[chrysler kid]

I apologize, I mixed up the bypass with the block off. Bypass you should be fine

http://www.dsmtuners.com/threads/fiav-blockoff-or-bypass.368668/

 

[chrysler kid]

First things first, have you done a boost leak test. It could be as simple as your blow off valve leaking

 

[Dawson159]

First things first, have you done a boost leak test. It could be as simple as your blow off valve leaking

I have a small leak in my shaft seals in the throttle body but that’s the only one and It runs fine after the idle settles so i don’t think it’s a boost leak?

 

[shinzon]

I have a small leak in my shaft seals in the throttle body but that’s the only one and It runs fine after the idle settles so i don’t think it’s a boost leak?

Idle surge is often caused by air bypassing a closed throttle plate--that means it could be, among a few other things, stuck open throttle plate/misadjusted throttle cable, TB gasket, BISS o-ring, injector seals, vacuum hoses, or intake manifold gasket. If your shaft seals are leaking, you've likely found your issue. Failing that, if idle stabilizes after the engine gets warm, it may be your intake manifold gasket: as the engine heats up, the metal expands and crushes the gasket making it seal better.

 

[chrysler kid]

I mean idle surge can also be vacuum leak too. It could be the mass air flow sensor failing. They say if you tap it hard with your finger and the idle changes the mass air flow sensor is going bad

My favorite way to check for vacuum leaks is by ear, just keep wiggling vacuum hoses and fuel Injectors until you hear a hiss noise or stop hearing a hiss

I have a 98 gst and deleting my EGR messed with my engine. The car expected a certain air flow from the EGR at a certain condition and it would run funny, however it ultimately did trigger a check engine light. So if you have the 98 ECU it could also be about to trip a EGR code

 

[Dawson159]

I mean idle surge can also be vacuum leak too. It could be the mass air flow sensor failing. They say if you tap it hard with your finger and the idle changes the mass air flow sensor is going bad

My favorite way to check for vacuum leaks is by ear, just keep wiggling vacuum hoses and fuel Injectors until you hear a hiss noise or stop hearing a hiss

I have a 98 gst and deleting my EGR messed with my engine. The car expected a certain air flow from the EGR at a certain condition and it would run funny, however it ultimately did trigger a check engine light. So if you have the 98 ECU it could also be about to trip a EGR code

The thing that confuses me the most is that it fixes itself after a few minutes it takes longer if the car has been sitting overnight so I think it might be the intake manifold gasket like what shinzon said

 

[Dawson159]

I mean idle surge can also be vacuum leak too. It could be the mass air flow sensor failing. They say if you tap it hard with your finger and the idle changes the mass air flow sensor is going bad

My favorite way to check for vacuum leaks is by ear, just keep wiggling vacuum hoses and fuel Injectors until you hear a hiss noise or stop hearing a hiss

I have a 98 gst and deleting my EGR messed with my engine. The car expected a certain air flow from the EGR at a certain condition and it would run funny, however it ultimately did trigger a check engine light. So if you have the 98 ECU it could also be about to trip a EGR code

What do U mean when U say the blocked egr messed with ur car?

 

[motomattx]

First, how did you bypass the fiav? if you looped the lines for the coolant it wont work, the only way to get rid of the fiav is to literally get rid of it and install a block off plate, anything else can and will cause idle problems.

 

[Dawson159]

First, how did you bypass the fiav? if you looped the lines for the coolant it wont work, the only way to get rid of the fiav is to literally get rid of it and install a block off plate, anything else can and will cause idle problems.

If it doesn’t work then what’s the point of the bypass plate in the first place?

 

[drcolt]

Leak down test for sure. And change all seals gaskets anyway from tb to intake manifold.
I had idle surge and with a quick leak down test noticed small leaks at Tb and injectors. I may have something small at the manifold, that's the only one I didn't change and now it idle much better.
I also fully cleaned the TB when cleaning the shaft seals.
Long of the short. Leak down test first.

 

[Dawson159]

Leak down test for sure. And change all seals gaskets anyway from tb to intake manifold.
I had idle surge and with a quick leak down test noticed small leaks at Tb and injectors. I may have something small at the manifold, that's the only one I didn't change and now it idle much better.
I also fully cleaned the TB when cleaning the shaft seals.
Long of the short. Leak down test first.

I don’t get how it can be a leak if the car runs perfectly fine after the idle fixes itself. It feels like there is too much fuel going into the cylinders and is bogging down as well as surging then when I step on the pedal it clears the cylinders out then when the idle fixes itself it’s like the computer tells the car to not put as much fuel then it runs fine. This is just an educated guess of what I feel like is happening because it’s hard to explain over a forum post. The car is running really rich it has since I bought the car and it needs to be tuned so that’s why I think it’s getting too much fuel

First, how did you bypass the fiav? if you looped the lines for the coolant it wont work, the only way to get rid of the fiav is to literally get rid of it and install a block off plate, anything else can and will cause idle problems.

I bypassed it with a plate and looped the coolant lines what did I do wrong?

 

[drcolt]

You're running link v3? what injectors, fuel pump and fuel presure regulator?
You've checked base timing?
So boost leak tested?

 

[AWD-Tony]

Boost leak test boost leak test boost leak test. Check the hose to pcv valve as well. Check the connector on the iac and make sure the wires are ok. My 2g had a broken wire on that connector which caused it happen occasionally and eventually got worse.

 

[Dawson159]

You're running link v3? what injectors, fuel pump and fuel presure regulator?
You've checked base timing?
So boost leak tested?

Link v3, stock injectors, walbro 255 pump, I need to check timing, only a small leak in throttle body shaft seals

 

[Dawson159]

Boost leak test boost leak test boost leak test. Check the hose to pcv valve as well. Check the connector on the iac and make sure the wires are ok. My 2g had a broken wire on that connector which caused it happen occasionally and eventually got worse.

But if it was a boost leak wouldn’t it never fix itself cuz it’s constantly leaking?

 

[AWD-Tony]

Sounds like you did a blt. Replace the shaft seals and do another blt. You won’t know if there’s another leak until you fix that but it’ll most likely be a smaller leak.

 

[AWD-Tony]

Correct. It will never fix a boost leak but it does change your fuel trim if it’s getting different reading then MAF

 

[drcolt]

So what did you last touch? Was it ever running good? If so, what was the last thing that was messed with?

 

[Dawson159]

So what did you last touch? Was it ever running good? If so, what was the last thing that was messed with?

It has never not had idle surge since I bought it I’ve only had it had it for around 3 months and it had idle surge and all the signs were leading to bad fiav so I bypassed it and it runs better now but still idle surges under certain conditions

 

[Gandalf]

Your fiav wasn't opening when cold allowing the air it needs to idle. So you blocked it off which essentially did nothing. The problem wasn't that it was staying open, it's that it was staying closed. Idle surge when getting too much air surges between 1200-2000. Yours surges between 300-800, which indicates lack of needed air. You don't need a leak down test. You need a functional fiav.

This is not a guess.

 

[Gandalf]

You should validate that someone didn't remove the freeze plug on the fiav and rotate the valve clockwise, effectively preventing it from opening. This is the method used to block it off without a bypass plate.

 

[Dawson159]

Your fiav wasn't opening when cold allowing the air it needs to idle. So you blocked it off which essentially did nothing. The problem wasn't that it was staying open, it's that it was staying closed. Idle surge when getting too much air surges between 1200-2000. Yours surges between 300-800, which indicates lack of needed air. You don't need a leak down test. You need a functional fiav.

This is not a guess.

So remove the plate and make sure it is not stuck closed then go from there?