3.2 Surging Idle

[sidebp]

Hi,

Firstly, hello, I recently joined having bought an '88 G50 3.2 Sport this year.

After some advice on an issue that's driving me crazy.

• Since I've had my car its had a jumpy idle when cold, in an effort to resolve I recently removed the ICV and cleaned, upon refitting the idle was much worse, surging between 1k and 2k RPM.
• After doing various checks I decided that I would replace the ICV (it was an '82 part so likely not original). I ordered a new valve, excitedly fitted and for good measure replaced the jubilee clips as the others were a bit slack.
• Now my car has a fast but steady idle at 1,2k RPM however as the car warms the RPM's gradually rise, when fully hot the idle surges between 1,2k and 1,7k. If i leave the car overnight its fast but steady when cold again.
• When driving, if I close the throttle the car pulls gently and revs climb, the only way to slow the car is to ride the brakes or keep changing up

I have:

• Checked voltage to ICV which is 12.6v (the valve also hums when powered on)
• Checked the resistance on the idle microswitch in open and closed position and that it is clicking on and off as the throttle opens and closes
• Overridden the ICV and attempted to set the idle but turning the screw seems to do nothing

My suspicion is that it is a mix problem, caused by a vacuum leak (I cant find anything obvious in the ICV area where I've been working) or potentially the car just needs the mix resetting but I am not sure. Speaking to a garage they are suggesting the AFM might be faulty or perhaps the ECU given its linked to temperature rises; the garage has a good rep but I am struggling to understand why replacing the ICV would now expose issues in those parts, a vacuum leak or setting the AFM up again feels more probable?

Any ideas on what to check and in what order? The garage can't fit me in until mid-Jan so its a long wait with a relatively new car

Thanks in advance.

[ischmitz]

Welcome to the forum and congrats to your 3.2.

As far as unstable idle do a search here and you will find lots of very informative threads dealing with this topic. In general you're correct that intake leaks affecting mixture at idle account for the vast majority of poor idle performance. Before you adjust anything it makes a lot of sense to track down any potential intake leaks. The main culprits are:

- deteriorating rubber hoses on the intake
- brake booster vacuum supply
- intake runner gaskets

Then it comes down to properly functioning sensors (CHT, IAT, AFM) that tell the DME how much fuel to inject and correct adjustment of idle mixture and throttle stop. Unfortunately, once someone messed with the adjustments to mask a problem you have to go back to the basics.

Cheers,
Ingo

[john walker's workshop]

Try turning the idle speed down to 880 first.

[Tea Tray]

Sounds like my ‘87 3.2. Behind the throttle body is a real tight mess of vacuum lines including the large line that goes to the vac brake booster up front, the venturi assy, and about a dozen clamps.
Remove the air filter box, air blower and ducts, and look around at all the lines for cracks, loose clamps, etc.
Most importantly, check your rubber fuel lines.

[mysocal911]

Originally Posted by sidebp

[*] Checked voltage to ICV which is 12.6v (he valve also hums when powered on)[*] Checked the resistance on the idle microswitch in open and closed position and that it is clicking on and off as the throttle opens and closes[*] Overridden the ICV and attempted to set the idle but turning the screw seems to do nothing[/LIST]
My suspicion is that it is a mix problem, caused by a vacuum leak (I cant find anything obvious in the ICV area where I've been working) or potentially the car just needs the mix resetting but I am not sure.

Check this link for evaluating the ICV;

Idle Valve Testing, post #20, Bench testing Carrera Idle Control Valve

[sidebp]

Originally Posted by john walker's workshop

Try turning the idle speed down to 880 first.

I'll give it another go but when I did this before (inc overriding valve), turning the screw seem to have no effect.

[sidebp]

Originally Posted by mysocal911

Check this link for evaluating the ICV;

Idle Valve Testing, post #20, Bench testing Carrera Idle Control Valve

Thanks, I actually followed this on the old valve, it was opening and closing with a 9v battery but when it was on the car there was no hum and resistance was not per Bentley manual so I decided to replace in the end. The new valve is humming and resistances per spec.

[proporsche]

Did your garage checked the fuel mixture??


Ivan

[sidebp]

Can't get an appointment til mid Jan. Looking for another garage (this one has a good rep though hence the delay I guess)

[911obgyn]

Vacuum leaks!
Entire crankase venting system, intake needs to be checked. Oil cap to brake booster and cruise control . The little rubber tees behind the air cleaner that connect to nylon vacuum lines are cheap. Throttle body has a couple of vacuum lines so does fuel pressure regulator. There should be a diagram

[jlex]

Originally Posted by sidebp

I'll give it another go but when I did this before (inc overriding valve), turning the screw seem to have no effect.

That's because you didn't jumper the leads to take the ICV valve out of the mix.
Search how to adjust idle on the 3.2 on this forum. There should be a picture of the socket you need to jumper mounted on the left side of the engine compartment.
I'm in agreement with John Walker on this... adjust your idle first.

[proporsche]

there is a relay for the plug and idle adjustment but wire will do

Ivan

[sidebp]

Originally Posted by proporsche

there is a relay for the plug and idle adjustment but wire will do

Ivan

I did use wire to jumper the connections indicated. Perhaps it didn't have sufficient contact - will try again.

[ischmitz]

It seems you're already far down the road of adjustments. However, contrary to some opinions here I'd always question why an adjustment is required in the first place. More often than not there is a primary problem that developed over time or suddenly (e.g. intake vacuum leak, fuel pressure or fuel delivery issues, condition of ignition components, worn AFM) resulting in poor running. Idle is particularly affected because intake leaks (un-metered air) have the biggest impact at idle.

Adjustments are then made in an attempt to compensate. However, if the underlying issue is not subtle the adjustment itself runs out of range or won't be effective. I would always go back and confirm basics check out before messing with idle adjustments:
- intake vacuum leaks
- fuel pressure and fuel delivery
- general upkeep (plugs, rotor, wires, valve adjustment, etc.)
- sensors (CHT, AFM, IAT)

Good luck and keep us posted on progress

[proporsche]

here is a guide from Porsche 911 manual how to adjust fuel mix....

[aus911]

Hi Ivan,
Do you have more info about this relay, My guess is the switch shorts jacks B and C together, but what do the green and red LEDs indicate? Did you make this?? Is this connector used for anything else?

Cheers
Ray

Originally Posted by proporsche

there is a relay for the plug and idle adjustment but wire will do

Ivan

[john walker's workshop]

You can pop the top off an old black relay and simply push the top contact down with your finger to do the same thing, if I remember right.

[mysocal911]

Originally Posted by jlex

That's because you didn't jumper the leads to take the ICV valve out of the mix.
Search how to adjust idle on the 3.2 on this forum. There should be a picture of the socket you need to jumper mounted on the left side of the engine compartment.
I'm in agreement with John Walker on this... adjust your idle first.

You are aware that if the DME ECM ICV drivers are damaged, e.g. open/shorted, the jumper will have no effect, right?

[sidebp]

Originally Posted by mysocal911

You are aware that if the DME ECM ICV drivers are damaged, e.g. open/shorted, the jumper will have no effect, right?

Wasn't aware of this. Is it something I can test for?

Thanks

[proporsche]

that relay is a tool for 944 testing ..it is simple tool i got from the dealer back in the 1980`s...here
i liked the idea ..again wire does the same

Ivan