Idle trouble - Time to fess up...
 

I have to cleanse my conscience, and let you in on my bonehead move.

I have been grappling with a "hunting" idle for three weeks now, and it seems that a very simple mistake has resulted in more learning than I had bargained on. The good news is that just about every potential area of concern has been renewed, replaced, or confirmed good. I have a refurbished Air Flow Meter ($350), a new Idle Control Valve ($100), all new sensors (Reference, speed, Head temp, O2, TDC), replaced just about every clamp on every hose, all to no avail.

Today, I took the car to the mechanic to have him reconfirm the CO readings following the installation of the refurbished AFM, and he says, "The arrow on the ICV should be pointing the other way, no?"

All this time, the valve had been installed backwards, and neither he nor I ever noticed until today. I quickly swap it around this morning, and head home to let her cool down before starting her up "cold".

Turned the key, fires right up, idles rises to around 1100... and sits there like she's supposed to. After she warms a little, the idle drops into the 800-900 range and steady as a rock.

Unbelievable.

Hope you rkept all of the old parts. Evidently, they are all good. Now you have some backups. I love having backups on the shelf. Not running right? No problemo, just pull a part off the shelf and plug it in. I have a whole CIS system on the shelf, fuel pump, alternator, MSD box, cap and rotor, etc.

Definitely. Spare parts bin is full.

Congratulations on your fix. Sorry to hear it cost so much in parts. Like the others said, now you have spares, or you've got some swap meet items.

I'm just happy to be idling smooth. It was driving me nuts.

Boy, most people have to go to a real college to get an education that expensive. Is that considered a "self study" program? :)

Tell me about it. It could have been worse, I was on the verge of ordering a DME.

Holy crap! You mean it's not supposed to point up?

rick, so i assume you may be ready for a sunday morning drive? or maybe an autoX? good job on the fix. you definately need to break a few eggs to make an omlette. in your case, looks like you went back to the store bought a few more eggs, and still ended up with an 3-egg omlette :) i have done the same. starter, WUR both come to mind. but i sold them both, CHEAP. oh, i kept the extra clutch cable.

cliff

Purry, nope. Arrow down, label facing you.

THIS JUST IN:
Still hunting at cold startup. Not as severe, but I am losing my mind. Going to try swapping a DME to see if mine is screwed up. Stay tuned.

I know that you have replaced it but it sounds like the O2 sensor to me. Or, if its a three wire then the O2 heater controller. Actually if it is the controller I believe the idle would improve after the sensor heats up.

Good Luck

check your idle mixture, and make sure the base idle speed is set correctly. Assuming you fixed all air leaks, you may have a worn ISV.

Thanks for the input, guys.

I think the idle speed, mixture settings may be involved. With all the adjusting and replacing, I have no baseline anymore. My mech loaned me a propane bottle with a hose outlet to use for finding vacuum leaks, and when I released some into the intake, it nearly stalled, when it should have increased the idle. This was with the motor warm, and not "hunting". He wants me to let it cool and try it again cold, while it's hunting. The AFM is newly refurbished, and the CO adjustment is whatever they left it at, and sealed.

I think I'm getting closer. It sure runs great when it's warm, though.

Steve, I replaced the Idle Control Valve (ICV). Is that also known as the ISV?

If it runs great when its warm there is a simple solution... never turn it off.

Idle hunts when cold because whatever the idle mixture is at, and whatever the idle speed is adjusted to at the throttle body does not match what the DME wants to see, which is Lambda=1 and 880 rpm. So it hunts trying to adjust to it, but the latency of mechanical parts and oscillating feedback from the rpm and O2 sensors causes a hunting oscillaition until the engine warms up.

ISV, IAC, ICV, it's all the same.

Thanks Doug, already considered that, but I can't afford the gas!

Steve, it seems that swaping my DME would easily isolate the issue. Doesn't the DME "ignore" sensors initially at startup, running in a "closed loop" until it warms enough to trust the readings? If this is the case, it would seem that the "closed loop" outputs from the DME would be the most likely culprit since I'm only hunting when cold.

The propane bottle is a huge fire hazard. You can accomplish the same thing with a spray bottle full of water.

A quick way to check for a vacuum leak is to remove the Oil filler cap with the car running. If there aren't any leaks the idle should slow when you remove the cap

Thanks, Carl

I was very conservative with the propane, and expressed those same concerens to my mech, who showed me how he uses it, and made me feel comfortable using it.

The idle slows when the cap is removed, so I am looking more closely at the mixture.

You said your ISV was installed reverse right? Again, you still need to check and adjust the base idle speed and idle fuel mixture.

Right, it was reversed. The AFM was removed and sent away to be refurbished. It came back with the CO adjustment screw sealed, so no CO adjustment has ben made with it installed on the car. I am dropping the car off for my mech to hook up to the gas analyzer for an accurate CO adjustment.

Thanks for your help.

UPDATE-

Picked up the car today from my mech. CO adjustment AFU. Properly adjusted with gas analyzer. Purring like a kitten right now. I'll be holding my breath when I turn the key tomorrow morning.

It sounds like you got the problem licked. Congrats!

I sure hope so. Thanks

Not clear on what kind of idle hunt you had. Was it a fast hunt or a lazy slow one?

Joe

It was actually both at times, depending on my idle screw setting at the time. I found myself adjusting the idle screw almost all the way in when it was cold, which would significantly reduce and shorten the duration of the hunting. I'm happy to report the CO adjustment seems to have been the final piece of the puzzle. She was steady as a rock at 4am today.

Edit: the idle would vary from 600 - 1500 in a fairly quick rythym, and settle after approximately 60 seconds if left alone. If I adjusted the idle screw nearly all the way in (CW), it would recover and idle normally with 10-15 seconds.

I suspect you may have a very common vacuum leak to be found on 3.2's in the form of loose intake manifold nuts that allow that extra air into your engine bypassing the idle air adjustment screw causing the fast idle hunt.

Just a hunch,

Joe

No leak, Joe.

It turned out to be the CO adjustment. Once my mech put it on a gas analyzer, he found it was severely rich, causing the hunting idle. Once he adjusted it back to normal, it starts and runs steady as a rock, cold or hot.

Good to hear it was that simple!

Cheers,

Joe

hooray!

Let's go for a drive!

Zoanas:

I had the same hunting problem in my 84, and did almost everything you did (new ICV, head temp sensor, O2 sensor, etc.). Like you, my problem turned out to be mixture. Sometimes the easiest solutions are the best.

Now, go drive!! SmileWavy

Scott

Still purring...

Just a bump for others having similar problems.

let's lower that car!

I'm thinking the same thing, vash. I just don't have a weekend clear for a couple of weeks. I'll keep you posted.

Hey, I want to lower mine as well. Let us know when you're gong to tackle yours.

cool, here we go again!

Hmmm, mine does a similar thing, but it's intermittent. She hunts and then stabilises, but sometimes while she hunts, she'll drop to about 400RPM's nd then stalls. Grrrr! It's annoying! I disconnected the Oxygen sensor though, so the Motronics runs the mixture richer than normal. The GT2-EVO CAMs aren't really helping either as the idle is even lumpier than when it had the stock Carrera CAMs.

Hey I am having the same exact problem after installing a new AFM.

Will get the CO% adjusted and report back about the hunting being cured.

I have been thru all the air leaks possible, even a new oil cap seal.

will report back but thought it good to wake up this simple-solution thread--unlike some others, where I learned a lot!

Still steady after all these months. Good luck, indigo, I hope it solves your problem. Hunting idle is the most frustrating problem I've had so far, but it did force me to dive in and learn some things.

Does the Bently manual have this pocedure outlined? My friend has a gas analyzer, and im having a similar problem