Idle Surge

[olaf811]

I'm having quite a hard time Diagnosing my idle surge, and have searched through many forums for answers, and tried the recommendations, but to no avail.

Car: 1993 Talon TSI

Symptoms:
When car is cold, you start it up and idle instantly starts to surge up and down in around 1 second repititions. This persists until the car is warmed up and then stops once reaching normal operating temp.

Process in trying to solve problems:
- Sprayed carb cleaner around intake hoses and seals. (no apparent leaks)
- Taken off throttle body and cleaned (no change)
- Tested ISC unit with ohm-meter. Tested bad. Replaced with part from junkyard that tested within acceptable range. (no change)
- Tried to set BISS screw to proper idle (750rpm +- 50rpm followed instructions for car to be fully warmed etc.) but idle would not drop below 1100RPM. Everything was done according to instructions, with proper sensors grounded out to set BISS.
- Adjusted IPS (Idle position switch) with ohm meter as per instructions (15/16 turn past point of connection, in order to try to let idle lower to 750rpm)
- Tried to set BISS again. Still would not drop lower than 1100RPM.

Since doing the last IPS adjustment (could be coincidental) the car now seems to be surging when warm too. Not sure if the problem is getting worse, or if something was adjusted improperly?

I read that if after adjusting the IPS and you STILL cannot adjust the BISS to get the idle to drop to 750RPM then it points to a leak in the FIAV. And that if the FIAV is leaking you will need a new throttle body. I'm wondering what the next step would be? I have read the idle surge FAQ, and need to have another look over it I assume to make sure I have caught most of it. Just looking for recommendations as to what I can test next, or possibly replace (Pick'n'pull if possible). I have a multimeter, and a novice skill at fixing cars, but am great at following instruction and learning.

Please help with this issue, as the surging is a little dangerous during driving!

[Non-Issue's]
I have read in a few other posts that people are sometimes having their car stall or sputter when they push in the clutch. This has never happened with this car. The surge always makes it rev higher than normal, never does it stall or sputter out.


Thanks in advance!

 

[dustinmp3]

the only thing i could have you do is check you throttle position sensor
or make sure that the screw isn't leaking at start up.

another thing can be the iac motor even though it passes with the meter

try to find parts off a friends car

but when you try to set the screw and it wouldn't drop that means their is one of them not working
hope this helps

 

[tunethis]

Either you a major vac leak, a stuck fiav, or maybe a bad coolant temp. sensor. Could be something else but, I'd look at and/or test those first. You can pick up a fiav from a junkyard and put on a a new fiav gasket if your fiav is stuck. When did all this start? Have you performed a boost leak test yet?

I have a similar issue but, without the surging. At start up, my car will idle at 2400rpm's and will drop to 1400rpm's when warm. The idle was slightly lower before swapping out to a newer ISC. Adjusting the biss does not lower the idle. I did find a loose hose, a leak at the biss screw and a leak at the shaft seals. I fixed all but the shaft seals. They are on order though. Hopefully, that will fix my high idle. I have an auto so, while in gear, the idle is around 800rpm's, which isn't bad. I will also check my fiav when I get a chance.

 

[DSMopar]

I don't know why people with idle surge issues start with the IAC or others... 90% of the time it's the FIAV... it's a mechanical component that runs coolant through it, how reliable do you think that is?

 

[Lofty]

I don't know why people with idle surge issues start with the IAC or others... 90% of the time it's the FIAV... it's a mechanical component that runs coolant through it, how reliable do you think that is?

No... Do you even know what a FIAV is?

90% it's the IAC.. Without a doubt.

 

[Quirk]

No... Do you even know what a FIAV is?

90% it's the IAC.. Without a doubt.

Yea it's the IAC, your sensor is going bad. Happening on my 2g, but not exactly like that mines the other way around. When my car heats up the rpms surge and bounce everywhere. Replace the IAC.

 

[Lofty]

Yea it's the IAC, your sensor is going bad. Happening on my 2g, but not exactly like that mines the other way around. When my car heats up the rpms surge and bounce everywhere. Replace the IAC.

Even with a faulty FIAV your car can be adjusted to run JUST fine.

Find a friend with a good ISC to borrow, or go find a black one out of a 2g in a junkyard.

 

[talonDSMerr]

I had a problem very similar to this. Idle surge at startup until warm and then regular idles after. It also surged when the clutch was pressed in and the car cruised in neutral. It turned out to be a faulty FIAV, not uncommon.

There are a couple ways unmetered air can get through the throttle body, which is the cause of idle surge:

-Boost leaks after the maf sensor
-ISC
-FIAV
-BISS screw
-Throttle body gaskets

You've already tested out a used ISC and it was in the normal operating range so that's out of the equation. You've adjusted the IPS correctly so the throttle plate isn't open more than it should be. You tried lowering the idle rpm by screwing in the BISS screw but couldn't, so the o-ring there is not causing the excess air going through the throttle body. I'm assuming you've already performed a boost leak test and found that the TB gaskets are not leaking.

That leaves us with the FIAV. There isn't any real way to diagnose if it is working or not, but one way (trial and error) would be to remove the bottom half of the TB and place an FIAV bypass plate between the TB and FIAV. When doing this, you need to make sure your FIAV gasket is in good shape or you'll have to buy a new one to prevent leaks. Try this and see if it fixes your idle problem (it fixed mine). The bypass plate can be had for $10 shipped, PM me if you need help finding it.

 

[Trav83]

the only thing i could have you do is check you throttle position sensor
or make sure that the screw isn't leaking at start up.

another thing can be the iac motor even though it passes with the meter

try to find parts off a friends car

but when you try to set the screw and it wouldn't drop that means their is one of them not working
hope this helps

I agree, try your TPS sensor, sometimes there not sitting where they should be or they can go bad. I think the vfaq has a 'how to' on it. I know when I tested mine it wasn't sitting quite right, need to be moved just a tad.

 

[DSM_Zak]

Just because the IAC tests good with the ohm range, it can still be bad. Try a couple different ones. Look for a black one, its the newer style, and should take care of that issue.

90% of the time it's the IAC. I have 2 good IACs in my posession, so if you are having trouble finding one shoot me a PM. One of them has a 3 year warranty.

Good luck!

 

[anmGST]

My car does this also but when its warm the idle will drop so far down the car stalls. It will idle at 1200-1300 and then sometimes just bottoms out and stalls.. What is the FIAV?? Thanx

 

[anmGST]

Could the caps be leaking on the ECU?