high idle..anyone solve it?

[talontedtsi1995]

I know there have been plenty of post made about the high idle problem, I have a 1996 talon tsi fwd and it will idle fine then out of the blue after driving for awhile it idles anywhere from 1,500 to 2,500 rpms, I tested all the sensors according to the Mits. Book and I fixed all boost leaks of whick I could find, the motor was rebuilt about a year ago therfor the throttle body is still clean. But, when I do the boost leak test it doesn't hold the pressure, such as the boost gauge reading 10lbs on the gauge, I use a regular hand pump and can not hear anything leaking, also used the soap+water, did anyone find out or fix thier high idle problem?

 

[Turbo Talon 111]

Mine has a slightly erratic idle issue. Its not the surge problem but is more like you are describing. I'm using a 1G TB and I believe the problem has to do with the seals that support the butterfly valve shaft. I plan on replacing mine soon to hopefully solve my problem. Mach V motorsports is the only place I have seen that sells the seals outright. Otherwise you'd have to figure out the size. There is a how-to out there on how to replace the seals which I think is on VFAQ but I could be wrong.
If you can grab the end of the shaft where the throttle cable attatches and wiggle it a decent amount up and down, side to side then that is a decent indication that those seals are getting bad.
Sometimes you will be able to get boost to seal when running a leak test but sometimes not. I think it has to do with valve position but I'm not sure. if you put a plug in the intercooler piping just before the TB you can easily check for leaks all through there. To be able to check the TB also you would have to get ahold of a plate and bolt it to the backside of the TB (where it attaches to the manifold).

 

[JohnCIV_Talon]

When it does this out of the blue after a while, it is probaby the isc. I know you said you tested it but, did you test if goes in and out? You can just take it off of the throttle body and turn the key on and off, and check to see if its moving in and out. The way I fixed my high idle, after everything was checked and working was blocking the fiav.

 

[talontedtsi1995]

how did you block off the fiav? also, taking off the isc from the throttle body, would that mean I would have to re adjust it when I put it back on if so how would I go about that?

 

[ekanddsm]

Blocking the fiav is easy work, j/b weld or get creative with the hole filler, but make sure it nice and hard, and bypass the coolant around it. The only adjust you would need to do is ti set the biss to whatever idle you want, 750 or higher.

 

[Hop]

I've made both an aluminum blockoff plate (removed the entire bottom half of the TB) and used a flat peice of a Coke can. The Coke can mod is easy but it doesn't look as clean. I used the BISS &/or throttle stop switch to set the idle now.

 

[daren_p]

Blocking the fiav is easy work, j/b weld or get creative with the hole filler, but make sure it nice and hard, and bypass the coolant around it. The only adjust you would need to do is ti set the biss to whatever idle you want, 750 or higher.

Thats is incorrect, the BISS isn't used to set your idle, thats the job of the ISC. The BISS is used to adjust the amount of air thats bypassed the throttle plate, which in turn is used to center the ISC in its adjustment range. Sometimes issues can cause things to get out of adjustment & the ISC gets pegged in one direction or the other. Once this happens & can no longer adjust any further, turning the BISS will adjust your idle but this is a side effect & not the proper way to set your idle.

To reset the ISC you just need to reset the ecu (disconnect the battery power). This will center the ISC in its adjustment upon powering things back up. The ecu doesn't get feedback from the actual ISC position so if you unplug the ISC while the cars running, your ISC will be out of adjustment & the ecu won't know this.

 

[ekanddsm]

then what the hell does BISS stand for? please educate me then

 

[Hop]

If you block the FIAV AND the ISC hole then the only way to adjust idle speed IS the BISS or stop switch.

 

[Hop]

Base Idle Set Screw

 

[ekanddsm]

Thats what I thought too. But then again I play in 1gen land with stoopid obd1, Obd2 cars doing have a learning capable idle map, and by disconnecting the ecu, depowering the car and discharging caps in the ecu goes back to default, and yes an ISC doenst know where it is thats why it responds to rpm. An ISC will need to be frozen to set the BISS properly. so dont unplug the ISC, follow the manual to get manual results.

Oh yeah block your fiav for desired idle control.

 

[daren_p]

Thats what I thought too. But then again I play in 1gen land with stoopid obd1, Obd2 cars doing have a learning capable idle map, and by disconnecting the ecu, depowering the car and discharging caps in the ecu goes back to default, and yes an ISC doenst know where it is thats why it responds to rpm. An ISC will need to be frozen to set the BISS properly. so dont unplug the ISC, follow the manual to get manual results.

Oh yeah block your fiav for desired idle control.

My post above was refering to 2g cars, & guys who just have the car running & tweek the BISS to achieve the correct idle, which isn't how you achieve proper adjustment & if it does allow for proper idle, you probably have other issues. I guess on a 1g you can properly adjust the BISS once you've grounded the proper connectors. We don't have this option being 2g's, so thats where DSMLink comes into play or an expensive scan tool.

 

[THE REAL DEAL]

well i fixed my high idle by replacing my gutted MAS with a MAS with both honeycombs. but now i have idle surge.

 

[Talesin]

Check for a vacuum leak. TB/mani gasket, intake manifold/head gaskets first. A boost leak test will usually make these show, so long as it's done with the valves non-overlapped and the TB plate open. Vacuum hoses being disconnected are your next likely suspect, and will also be easily located during a boost leak test. They're just rubber, and do degrade over time, and develop leaks.

On a 1G:
The BISS set connector that needs to be grounded is on the firewall, right behind the stock battery box. It has a plug in it (to prevent corrosion/other nasties) so take that out. Use an alligator clip to ground the single pin (small, the large 'pin' is just a piece of plastic) to the body. You'll also need to ground a specific pin on the ODBI connector to the body to put it into idle adjust mode, where the ECU goes 'hands off' and you can freely use the BISS to set your idle rpm properly, at 750. Make sure your timing is set correctly before setting the BISS (same connector on the firewall needs to be grounded, but the pin on the ODBI port must NOT be grounded), or you'll have problems getting the idle to cooperate due to wonky timing.