High idle out of nowhere! Some surging...

[tsi1991awd]

So for the last few days my car has started up fine but when its fully cold, it will idle like normal then after a minute or so, it will surge a bit. Only 100 or 200 rpm. When fully warmed up its fine. But its been idling a bit above 1000, maybe 1100 or so, so I turned the BISS screw and got it back down to 800. But I've been having to turn it almost every time I've started the car, so I'm not sure if its blowing out a bit or what.

But today, I put my forward facing filter bracket on and when I started the car, it idled at 2,500 and then started surging....again 100 or 200 rpm. So I blipped the throttle a bit and it went over 3,000 and stayed.

Turned car off, started again....surged, let it warm up and it went down a bit, maybe 1500 but was still surging. And after it was fully warmed up, the idle was normal and I revved the engine to see if it would surge or have a high idle and it was normal.

A while back I removed the vacuum lines from the TB, charcoal canister and EGR. Everything has been fine. I checked the vacuum ports and they're still plugged (used vac caps)

Any ideas??? This is baffling me.

 

[tjbiker031]

yea the BISS could be backing out, next time you turn it, notice its position and see if it moves. And it wouldnt hurt to run a boost test, who knows....heres a link to help you out some, i had a idle/surging problem with my gst, turned out to be the IAC, hope this helps

General Idle Surge Discussion - Page 3 - DSM Forums: Mitsubishi Eclipse, Plymouth Laser, and Eagle Talon Forum: DSMtalk.com

 

[tsi1991awd]

To be honest I have no idea what it is, because it's only doing it when it's cold. The ISC only controls warm idle. This is a cold idle/warm up issue. Might be the FIAV but I have no idea...it's causing a really high idle, then surging. Then if I hold the throttle just a tiny bit, it'll idle at that rpm even when I let my foot off. Seems like a vacuum leak, but I've already blocked all the vacuum lines off! Then it hits a certain temperature and everything disappears. Then when it's fully warmed up, it idles like nothing ever happened. It's very strange.

 

[HBWaterfowler]

Hello,

I'm still a DSM noob, but I have been battling idle issues since day 1, so I can maybe offer some ideas from stuff that has worked for me.

I know there is some wax pellet in the TB that at cold start up is not melted, and once it melts it some how changes the idle.

It's very hard to tell what's going on in your car, I think we would need more information.

But I think a simple fix would be just to get a FIAV block off plate. I have had all kinds of problems with my ISC (brand new black plastic) and the IABV. The best thing you can do is block it all off, IMO. This would allow you to have a no air bypassing your TB, and all you have to do is turn up your BISS to allow more air under load. So you would just turn on your lights, heater/ac/sterro/everything you can, and set the idle to 800, then turn it all off and it should be fine.

Another idea is the boost/vac leak. That's always a problem.

 

[boopy D]

I agree with the block off. No matter what I did my idle went from 800 to 2000 then back to 800 over and over and over.Anytime I stopped my idle went up and down,up and down. Until I blocked it off.havn't had a problem since.

 

[tsi1991awd]

I might have to do that...but the thing is, I don't know why it would do that just all of a sudden....never know with these cars. Maybe ill get a blockoff plate and get rid of those coolant lines. I don't want to do it and have it not fix the problem though.

 

[Matrixhunter]

To fix your idle problem follow these steps exactly.


Disconnect and reconnect your battery to clear the ecu memory. Then warm up the engine to operating temperature and unplug or turn off anything putting extra load on electrical system, this includes the headlight + tailight fuses/radio etc.

Once this is done, ground the (ecu ground wire) it's located near the firewall behind the intake manifold area. This sets the Isc in a neutral position and now you can adjust the biss (set your idle to around 750 +-50 rpm.

Finally disconnect the ground wire and watch your car idle properly!