Another Idle Surge Question. Oh god.

[BaddAssGst]

Basically the car is surging and the idle is way to high. I've went through a few threads but I didn't see what I was looking for.

Before: The car idled good, stayed at 850, no idle surge.

After (complete motor swap, where the TB was rebuilt with new seals and what not): Car idles like garbage.

When I first start the car, it jumps to 2300 and slowly settles down into the 12-1400 range and surges back and forth. The TB was rebuilt but I'm thinking it's possible he used a bad lower half of the TB (FIAV). I said, eh it will go away when it's warm. It hasn't gone away and surges the whole time, warm or cold. A bad FIAV (fast idle air valve) should only surge until the wax pellets melt and should go away when it's wamred up.

- I've checked 2 ISCs, both in spec and neither changed.
- If I undo the high idle switch, the surge goes away but still idles at 2500.
- Boost leak test was done, no leaks.
- I've tried adjusting the BISS and even as low as it goes, it still idles at like 1100, still surging.

I have a custom e-prom chip and the idle was set to 900.

Any ideas? Rep points?

 

[steve]

When I first start the car, it jumps to 2300 and slowly settles down into the 12-1400 range and surges back and forth. The TB was rebuilt but I'm thinking it's possible he used a bad lower half of the TB (FIAV). I said, eh it will go away when it's warm. It hasn't gone away and surges the whole time, warm or cold. A bad FIAV (fast idle air valve) should only surge until the wax pellets melt and should go away when it's wamred up.

IMHO, a bad FIAV is one where it still idles high after the coolant has warmed up. (No/little change cold to hot)
The FIAV is just suposed to provide bypass air until the pellet melts and it closes. If it does that then I think a FIAV is good and the real cause is somewhere else.

What's I've noticed is after replacing the seals many throttle butterflys are misaligned and don't close right. I've heard that the black stuff around the outside edge of the plate isn't carbon but a epoxy used to provide a final seal. I don't know how accurate that is but I know that before I replaced the seals and really cleaned the TB my car never surged. Since, it been very touchy.

Steve

 

[BaddAssGst]

IMHO, a bad FIAV is one where it still idles high after the coolant has warmed up. (No/little change cold to hot)
The FIAV is just suposed to provide bypass air until the pellet melts and it closes. If it does that then I think a FIAV is good and the real cause is somewhere else.

What's I've noticed is after replacing the seals many throttle butterflys are misaligned and don't close right. I've heard that the black stuff around the outside edge of the plate isn't carbon but a epoxy used to provide a final seal. I don't know how accurate that is but I know that before I replaced the seals and really cleaned the TB my car never surged. Since, it been very touchy.

Steve

I think you just might be onto something here. The TB was just rebuilt and before that, I hadn't had any problems with my idle. It was thrown together and has been bad ever since then. Thanks for the help so far Steve.

As far as the FIAV, I've mostly noticed that it is a start-up problem. I had about 5 throttle bodies that I tested, 2 of which I knew were bad and I would end up with the same result. None of them were rebuilt but 2 of the FIAV were no good (although I'm actually not sure what goes bad in them).

Quick Edit... sorry Steve, I can't give you rep points until I pass some more around..

 

[drewvr4]

does anyone have pictures or specifically where these things are...ive pulled the engine twice...but never really looked into that area as part of the problem...thanks

 

[BaddAssGst]

does anyone have pictures or specifically where these things are...ive pulled the engine twice...but never really looked into that area as part of the problem...thanks

The FIAV is the lower half of your throttle body.

Here.

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Don't mind the bad art skills.

 

[gurmanator]

I had the same problem and it turned out to be a vacuum leak in a hose that goes to the tb...I took a can of brake clean and mist the vacuum hoses on the tb and boom I found the problem.

 

[BaddAssGst]

I had the same problem and it turned out to be a vacuum leak in a hose that goes to the tb...I took a can of brake clean and mist the vacuum hoses on the tb and boom I found the problem.

No vacuum leak could be as bad as my idle.

But in all honesty, 90% of my vacuum lines are gone so it's not that.

 

[steve]

No vacuum leak could be as bad as my idle.

Perhaps, but think about how little the BISS passage is and how much range it has over the idle before you start ruling out tiny vacuum leaks.

Steve

 

[BaddAssGst]

Perhaps, but think about how little the BISS passage is and how much range it has over the idle before you start ruling out tiny vacuum leaks.

Steve

A very good point, something tells me that isn't it though. I'll check all the lines tonight and come back with some more info.

I will also go and ahead and double check both ISCs and possibly reset of the TPS.

 

[BaddAssGst]

I double checked both ISCs and they appeared to be in spec.

I think Steve might be onto something, I'm going to try and swap throttle bodies and see if the idle goes away. I know I have a spare somewhere.

 

[BaddAssGst]

To bring this back to life..

We got around to checking out a few more things. All new vacuum lines where they should be, new vacuum caps where they are blocked off, a boost leak test was done, throttle cables were checked, etc.

I can't keep the idle under 1800. It starts and stays there.

Any ideas? I'm running out of them.

EDIT: The car doesn't surge anymore, just idles high.

 

[steve]

If the ide doesn't drop some as the coolant temps rise and you still have the coolant lines to the TB it sounds like the FIAV isn't working.

Steve

 

[BaddAssGst]

If the ide doesn't drop some as the coolant temps rise and you still have the coolant lines to the TB it sounds like the FIAV isn't working.

Steve

That's what I'm having trouble with. If I let the car idle itself until it reaches operating temp (210*), the idle will slowly drop to 1000 or so, which I'm okay with. But if the car gets driven, it seems like it wants to end up idling back at 1700.

If I ground out the diagnostic plug, and set the idle to 950, as soon as I pull off the aligator clip, it goes back to up 1200 or 1300.