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Dark Skies's Avatar
 
Join Date: Feb 2003
Location: United Kingdom.
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Barely idling problems.

I'm about a gnat's cock from going insane right now.

As mentioned previously I've been suffering an annoying problem with poor idling (shuddering on the edge of death) on my (early)85 fuel injected 944. It was mainly noticable when I switched the lights on or the radiator fan cut in. The problem has now progressed, although in truth it was never far from this before, to stalling at traffic lights or junctions. She's fine on the fly at motorway speeds.

My first question is this - why is it you always end up getting stuck behind a prat who can't read the road ahead, stops for no good reason at every clear junction, or drives at fifteen mph when you're trying to nurse a spluttering car home?

Secondly - I've checked or replaced the following recently with no change in the symptoms:

Timing and balance belts - Porsche fitted.
Spark plugs
Fuel filter
Air filter
Ignition leads
Coil
Distributor cap
Rotor
exchanged alternator (with regulator)
Battery (last July)
Checked all earth leads
checked all fuses and connections
Checked relays
Fresh fuel
Injectors (I removed them, attached a reservoir full of injector cleaner and operated them off a 1.5 volt battery harness to check they worked (all squirted the same volume of fluid in the same time - figured that they wouldn't all fail at once so although it's hardly a very technical approach it must prove they're at least reasonably in spec).

Bypassed the engine earth strap with a booster cable attached to the inlet manifold straight to the neg terminal of the battery.

Apart from the exchanged alternator (seemed to be low on output) which was borne out of desperation the rest was just done out of regular servicing.

Soooooooo ... anyone got any ideas why my car still won't idle but goes fine on a straight road? Fuel pump is a little old - worth replacing? I'd have thought idling would be good but top end would struggle rather than tother way round.

Starting to get a little desperate here - help would be much appreciated.
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1983 944 Lux (manual) 2.5 litre 8 valve na and no pas

1991 944 (automatic) 2.7 litre 16 valve na and pas

"I have only five words for you: From my cold, dead hands."
Old 09-24-2003, 12:30 PM
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Sounds like a failed idle air control valve, or a stuck air flow meter. Maybe also a wiring harnes problem between the AFM and the main harness.
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Old 09-24-2003, 01:07 PM
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Vacuum leak. Check the large duct from the AFS to the throttle body. The bosses for the large vacuum tubing crack at the base.

Also could be a vacuum leak in the brake booster diaphram. Or some of the large vacuum hose connections are cracked. Check at the idle control valve and the engine crank case scavenger vavle. Check all of them!
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Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
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Last edited by SoCal Driver; 09-24-2003 at 03:29 PM..
Old 09-24-2003, 01:22 PM
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won't a vacuum leak make for a higher idle
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87 951, K27/6, Almond Beige, 17" Turbotwist
87 944S, alpine white, 5sp died a violent death
84 944, silver/brown, auto, gone but not forgotten

"may the force be with you"
Old 09-24-2003, 02:13 PM
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Not an exterme leak like SoCal is talking about, the brake booster line is very large.
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Old 09-24-2003, 02:47 PM
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Quote:
Originally posted by bearone2
won't a vacuum leak make for a higher idle
If the leak is ahead of the throttle body no. The AFS sends a lower air flow signal and thus less fuel.

If the leak is between the throttle body and engine then yes it does result in a higher idle. Will also affect the AFS input.

Also check the DME engine temp sensor.
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Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!

Last edited by SoCal Driver; 09-24-2003 at 03:30 PM..
Old 09-24-2003, 03:27 PM
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i agree with the location of the leak in relation to the throttle valve.
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87 951, K27/6, Almond Beige, 17" Turbotwist
87 944S, alpine white, 5sp died a violent death
84 944, silver/brown, auto, gone but not forgotten

"may the force be with you"
Old 09-24-2003, 08:09 PM
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HURRAH! I finally fixed the problem for 2.50 !!! Cyber pints all round.

I think it was SoCal that directed me to check for poor earths so thanks for that. I DID check all the earthing points and they were all good wire with clean connections on shiny metal ... and yet....

Despite an apparently excellent, tight, clean connection twixt the big fat earth from the harness behind the engine to the firewall this proved to be the cause. I have no idea why this was faulty but I fixed it by placing a nine inch length of braided earthing strap (8mm eyelet type)) underneath the harness lead connection on the bulkhead and connected this to a stainless M8 screw through an existing hole in the top of the firewall on the drivers's side (passenger side for those of you who drive on the wrong side of the world).

Hey presto! Instant smooth running. I have no idea why putting a booster cable from the engine to the neg battery terminal didn't show this up but ...

Anyhow ... this sorted the problem and instantly revealed another ... my headlights no longer popped up!!! Surprisingly for me I sorted this out quite quickly too - seem that the connections in the lifter motor were a bit sloppy causing the relay that slots into them to cause poor connections. It appears that the poor idling compensated for this by jiggling the connections sufficiently to operate the motor - I figured this out when I flicked the relay with my finger and the lights immediatly flipped. Quick strip down and judicious use of a pair of pliers to tighten the female connections fixed this immediately.

I'm ready for the next problem now.
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1983 944 Lux (manual) 2.5 litre 8 valve na and no pas

1991 944 (automatic) 2.7 litre 16 valve na and pas

"I have only five words for you: From my cold, dead hands."
Old 09-25-2003, 04:26 AM
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Quote:
Originally posted by Dark Skies
[
I'm ready for the next problem now. [/B]

SPOKEN LIKE A VETERAN!!!


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Old 09-25-2003, 05:15 AM
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I'm about a gnat's cock from going insane right now.

NICE! I love learning new expressions for anger! The British have some cool sayings.

Congrats on the fix
Old 09-25-2003, 05:23 AM
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children, children, it's about time for a time out.
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87 951, K27/6, Almond Beige, 17" Turbotwist
87 944S, alpine white, 5sp died a violent death
84 944, silver/brown, auto, gone but not forgotten

"may the force be with you"
Old 09-25-2003, 09:09 AM
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Between the engine and the chassis. Grounds the magic silver box to the engine. The path of all the motivation spells!

Grounds!!! Why is it always the grounds!!!
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Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!
Old 09-25-2003, 10:20 AM
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