Idle speed adjustor

[motogman]

So the diagnosis for the idle fluctuation on my 3.2 L is down to the idle speed adjustor.

I can buy a new one from our host... which I will likely will go ahead with.

My question is ... besides cleaning the air flow end of it - which I have done but not fixed my idle problem, what other prospect is there for rebuilding or rennovating this unit?

[dshepp806]

I assume you're referring to the throttle adjustment screw (for idle)? If so, there's only the O-ring.

Best,

Doyle

[stlrj]

Originally Posted by motogman

So the diagnosis for the idle fluctuation on my 3.2 L is down to the idle speed adjustor.

I can buy a new one from our host... which I will likely will go ahead with.

My question is ... besides cleaning the air flow end of it - which I have done but not fixed my idle problem, what other prospect is there for rebuilding or rennovating this unit?

Did you try lowering the idle speed on the throttle body idle air bypass? Or base mixture?

[E Sully]

I don't know what steps you've taken yet to set your idle. Have you used a wire jumper to jump out the test port? The idle control valve (ICV) comes into play only when the idle position switch on the throttle valve is depressed. Have you made sure that you have the switch adjusted so the contacts are closed when your foot is off the gas pedal?

[motogman]

So... after reading some more threads and your comments here is what I know...

I think the ICV is working ok. with battery voltage (6v) it moves both directions easily. The resistances check out. It has been cleaned a few times.

The throttle position switch is set right and is working properly when checked for open/closed continuity.

After the first cleaning, I thought the surge had stopped and I thought all was well. But... when I next started the car it was there again. Sometimes worse (meaning it surges and dies) and sometimes better (meaning it surges what seems like a couple hundred RPM but doesn't die). Tonight after it warmed up it was surging moderately - after a few throttle blips it idled fine for a while, after a few more blips it was surging again. Very frustrating.

I have read some threads on transistors which operate the ICV circuit going bad in the ECM. I am a bit reluctant to go there quite yet.

I might look for a local Porsche owner with a 3.2 to try my ECM in their car before I go further in that direction.

What say the experts here for next steps?

[kidrock]

I would want to know if:

1) you still have a stock chip,
2) if you have checked to see if the 2 hoses behind your throttle body have not come loose,
3) if you have checked your fuel/air mixture, and
4) if you have attempted to set your base idle as suggested by Sully (Ed).

Your base idle for stock 84-86 should be 800 rpm. For 87-89, 880 rpm. If you're running a Steve Wong chip, 880 rpm.

All this should be checked before switching out the ECU, in my opinion. But if you have quick easy access to one, it definitely won't hurt.

[E Sully]

AFM is the next thing to check.
Air Flow Meter (AFM) - from "The 944 Motronic DME" by FR Wilk* ©2001 www.the944.com
Rejuvenating a Bosch Motronic Air Flow Meter - YouTube

[motogman]

Some answers...

1) you still have a stock chip, Kind of. I have a European ECU which has slightly different mapping but also have the US. Both do it.

2) if you have checked to see if the 2 hoses behind your throttle body have not come loose, I have checked these and there does't seem to be any loose/missing/off

3) if you have checked your fuel/air mixture, and How to check the mixture? I thought that is what the O2 sensor measures and then the ECU adjusts injection to get right??


4) if you have attempted to set your base idle as suggested by Sully (Ed). Not yet- something for today. Question: How does cold idle speed vary from warm idle speed? The engine idles fine for 2-3 minutes and then goes into this surge mode - very consistent.

Also.. The other night after reinstalling the ICV again, when started it surged, after reving the engine a few times it idled fine, after a few more revs it was surging again and continued to. Seemed odd to settle out for a time.

I will check idle speed today and also check vacuum leaks at the intake manifold gasket area as some have suggested. I look for and appreciate more of your ideas.

[Lorenfb]

"also check vacuum leaks at the intake manifold gasket"

Vacuum leaks DO NOT cause this type of a problem. That is total mis-information
and a WASTE of time. This gets continually re-posted when anyone has ANY type
of idle problem which is mis-leading! An air leak at the intake pipes will result
in a LOWER & POORER idle and NOT surging!

Here's the diagnostic method:

1. First, turn the idle bypass screw in and see if the surging stops.
If not, then continue with #2.
2. Disconnect and remove the idle valve & set it partially open by moving the vane.
3. Install the valve but do not connect the electrical connector.
4. Start the engine and observe the idle, if not about 700-900 repeat step #2
above to either open or close the vane slightly.
5. If the idle consistently idles O.K. under all operating conditions, then the
problem is related to the valve or the DME ECM. Then plug in the electrical
connector and the problem should re-occur which confirms either the valve
or the ECM. Make sure the valve has about 20 ohms between the center & outer pins.
6. If the idle still surges with the valve electrical connector disconnected then;
a. Unplug the O2 sensor if it has one.
b. Check the fuel pressure, should be about 36psi.
c. Try opening the idle mixture screw in the AFM.

[Smoove1010]

I'm following along closely - my 87 3.2, NA with 98K is doing something very similar - idles smoothly at about 950 at startup after a nice puff of blue smoke if it's been sitting a few days. A minute or so later - and suddenly as if a switch is thrown - idle slows down to +/- 800 and becomes inconsistent. When in this slower idle condition, idle becomes progressively bumpier until there's a slight surge or I blip the throttle. Motogman - does this match your symptoms?

Perhaps the O2 sensor heats up and triggers to ECM to take over idle control at this "switch" point?

ICV looks new, and I did the rattle/clean/lube thing. Ohms checked out fine. AFM test showed a nice smooth progression, though the track looked worn, and I'm pretty certain the pickup was repositioned already - this tells me the PO experienced the same issue. All vacuum lines were checked - that one on the switch behind the throttle body was off - but any changes there resulted in minimal improvement. If I remove the oil filler cap, idle get slower/bumpier, but recovers somewhat.

Last night I detected low-speed driveability issues - mild bucking and surging when driving in slow traffic, about 10-20 mph in 2nd gear, for instance. Not happy about that...

I'll be following Loren's steps this morning, doing the baseline idle set procedure, checking intake bolts, re-checking vacuum lines.

Maybe we need an "Ultimate Rough/Hunting/Surging Idle Thread?"

[motogman]

From LoreHere's the diagnostic method:

1. First, turn the idle bypass screw in and see if the surging stops.
If not, then continue with #2. No effect.
2. Disconnect and remove the idle valve & set it partially open by moving the vane.
3. Install the valve but do not connect the electrical connector.
4. Start the engine and observe the idle, if not about 700-900 repeat step #2
above to either open or close the vane slightly.
5. If the idle consistently idles O.K. under all operating conditions, then the
problem is related to the valve or the DME ECM. Then plug in the electrical
connector and the problem should re-occur which confirms either the valve
or the ECM. Make sure the valve has about 20 ohms between the center & outer pins.
6. If the idle still surges with the valve electrical connector disconnected then; Still surges with the ICV disconnected. Seems not much different but idle was higher.
a. Unplug the O2 sensor if it has one. I have SSI exhaust - not sure if I have an O2 sensor but will get it up on jack stands and see what I can find. Where should the O2 sensor be - just after the exhaust manifold? If this is "the problem" what haapens when I disconnect it? Surging stops but misture less controlled?
b. Check the fuel pressure, should be about 36psi.
c. Try opening the idle mixture screw in the AFM. Havn't tried yet.

I have seen some threads that suggest something about the track in the causing issues. I need to go do some more research on this (maybe) - what says you on this being the potential cause??? and if so what to do next.

[stlrj]

"Still surges with the ICV disconnected. Seems not much different but idle was higher."

That's because it has nothing to do with the ICV. Nobody seems to understand how the "fuel shut off on decell" strategy works and the role of idle speed and how it can play havoc with this feature.

[motogman]

So after seemingly not getting anywhere with this issue today, I decided to go out for a drive anyway because I wanted to get the car warm and change the oil.

About 10 miles to a gas station and it idled just fine there. Came back and still idleing fine.

I have the oil out and will put fresh in shortly. I will let you know what happens to the idle when it starts from cold tomorrow.

Oh - by the way... No O2 sensor. This is an 86 3.2 in a 73 RS clone with SSI exhaust. The SSI has the mount point for the O2 sensor but is plugged. The only thing I don't think I have done yet is fiddle with the idle mixture in the AFM.

[Lorenfb]

"Nobody seems to understand how the "fuel shut off on decell" strategy works and the role of idle speed and how it can play havoc with this feature."

Really? The tests explain clearly how to diagnose the idle system.
If the problem can't be determined by the SIMPLE & DETAILED post,
then it's time to find a good Porsche repair shop!

"I have seen some threads that suggest something about the track in the
causing issues."

Right, it's usually the ones than have mostly right hand turns.

[motogman]

LOL

"I have seen some threads that suggest something about the track in the
causing issues."

Right, it's usually the ones than have mostly right hand turns.

I will have to start doing ovals (going counter clockwise) rather than road race courses!

That was supposed to have read...


I have seen some threads that suggest something about the track in the AFM
causing issues.

[Smoove1010]

I had some success with this yesterday:
- Did a very thorough inspection of vacuum lines, used fusing tape over the short rubber piece behind the TB going to the brake booster; more fusing tape over the short piece that connects the PCV (or ambient air valve) near the oil tank;
- The rubber elbow going to the TB had a light coating of oily dirt - cleaned it thoroughly;
- Backed the idle adjust screw all the way out, the tip of the "screw" was covered in a sooty sludge-y gook that I cleaned, also used carb cleaner in the orifice, as well as cleaning out the TB, which was dirty as well;
- Checked ohms again on the ICV (20, 22.5, 42.5) and confirmed that the idle switch was operating and adjusted;
- Torqued the intake manifold bolts - each one required 1/2 turn to get to 18 ft/lbs;
- Though the AFM checked out OK last time, I re-positioned the wiper, re-checked for a nice linear voltage change.

On first startup, surged a few times but settled right down after 15 seconds. I did the jumper/idle adjust procedure, now it's idling rock-steady at about 900 rpm. I can't help but wonder if all the nasty gook inside the TB and the idle adjustment air passages wasn't the culprit.