Strangest idle surge EVER, can't find any answers!!

[tsi1991awd]

I was having a problem about a week and a half ago on cold warm ups...the car would surge while warming up and then stop after it was warmed up. I was thinking that could've been due to the FIAV but I wasn't sure. Then one day it just stopped and everything was fine.

Today a problem arose and I can't seem to find an answer anywhere. When fully warm, car idles at 1300 to 1500. Drive and everything is fine. Throw it in neutral while slowing down and braking and the car surges from 1000 to 1400. When I push the brake all the way down and come to a complete stop, it stops surging! If the car rolls at all, it will surge. If I'm completely stopped, I can move the steering wheel and it won't surge...so I don't think its load related. I don't know though. I was thinking maybe ISC motor, but I have no idea because it seems kind of intermittent and spastic.

Oh I know the answer.....ITS A DSM.

 

[Deepnine]

You BISS screw is set wrong/to high. Idle when warm should be under 1000U

Try scewing it a bit in until it works. Throttle body cleaning often helps too.

Maybe you ISC is not working too. Check that first.

Because the idle speed is a bit higher when moving, you hit the idle limiter 1500U when idle switch is enabled. Remove the idle switch plug it will work as temporary solution.

 

[tsi1991awd]

Everything was fine yesterday. I don't know how the BISS would just become backed out overnight from just sitting there all night.

 

[Marchev]

The same thing happened to me about beggining of december. when the car would warm up the RPMs would be all over between 1000 to 2000. what I did was change the idle air control valve, and the throttle position sensor. Now everything is running fine idling at 750

 

[Deepnine]

If it came that fast, it sounds like the iac.

 

[tsi1991awd]

If it is the IAC wouldn't it do it all the time though? Also, would the IAC cause the idle to be weird during warmups? I thought that was controlled by the FIAV....

 

[khartley]

Check to make sure your BISS is actually still there, it has been known to vibrate its way out.

Also make sure your throttle cable isn't sticking.

You might want to get one of the FIAV bypass plates, they have helped alot of people with idle problems. You just want to keep your ISC motor, so you don't want to get the blockoff plate. And unlike if you JB weld the ports shut, you can take the plate off if it doesn't help you.

 

[Colt4G63 also]

It was probably just really cold that day, and the ECU didn't have a workable idle strategy solved for those specific conditions.

BTW: That doesn't sound like a "strange" idle surge problem. All my 4G6 series engines, and people I know with 4G6 engines, have had that happen from time to time. I don't even move mine until it's mostly warmed up, partially for that reason.

The ECU tries to keep RPMs up a little when it's cold, vehicle rolling, and the idle switch is activated. This is done to prevent stalling. The problem is, with startup enrichment, and extra air, the engine begins to run away. When the ECU sees the idle switch pressed, and the and RPM above 1500, it cuts injector duty to zero. That's why it revs up, cuts, then revs up again, repeatedly.

My 93 Accord (winter beater) even did it for a few moments when I started it up ice cold, moved it 20 feet (pulling out of the garage), then tossed it back in park. Since I always remote start it, the ECU wasn't prepared for that specific idle related task at that temprature.

All you can really do is make sure your temp sensor is in spec, and your thermostat is working. Ohm out your IAC so you know that's in spec, and clean out your throttle body and IAC. Other than that, I can't see any reason you would have a problem.

If you can get an ice cold DSM to coast down your driveway in neutral without surging, please let me know what the trick is

 

[jrohner]

When fully warm, car idles at 1300 to 1500. Drive and everything is fine.

That's about the highest idle you can have without having idle surge. When it is colder, it will try idle faster yet, so it will surge. If your ISC doesn't work, set the idle to around 900-1000 when warmed up and you should be about right. If your ISC actually works (yeah right), you should set it so the ecu can properly adjust the idle.

Put a new o-ring on the BISS, when the o-ring is old, the BISS moves by itself and leaks boost.

 

[tsi1991awd]

Well the thing is, the car was fully warmed up. I never drive when its a cold engine.

But today I let it warm up fully and it was idling a bit above 1000, and the biss screw wasn't where I had it before. Before I screwed it all the way and backed it out two turns....it blew out by itself. How do I cure that? The o ring on it looks fine....I guess it could be messed up, but its not cracked or hard...still soft and looks/feels good.

 

[tsi1991awd]

I just wanted to check in and say thanks to everyone on the BISS screw idea. I took the screw back out and bought another o-ring...hey for 75cents after tax, why not? The old one I THOUGHT was still soft but after trying to take it off, it just snapped it half and was hard. Still SLIGHTLY pliable but hard. The new one slipped on easily and when I went to put the screw back in, it was actually giving a little resistance, like the o-ring was actually doing something. The last o-ring let the BISS move really easily in/out but the new one is snug. Took it out for a drive and wow, I wonder how much boost was actually leaking from that tiny thing because my car was spooling faster than ever. Thanks again....hopefully this solves my idle surging.