poor idle / stalling

[C2dweller]

As mentioned in my first post, the most urgent repair is the poor idle problem. Existing posts don't seem to match the problem I have, so I'll start another.

Symptoms - Car will start OK, but won't tick-over - stalls and is hard to crawl. Interestingly:
On Saturday - it did it to a lesser extent when I pulled it off the drive at the owners and seemed to be OK for the whole day - even during the inspection.
On Sunday it was fine for a quick drive and worked fine for the next 350 miles.

Then I took my father out for a 'fast lap'. After this it got worse.
After it cooled down it seemed much better. Drove last part of the 50 mile motorway journey home and it was OK until I got to the low speed stuff, when it got worse.
One final blast home and it was worse than ever.

Monday morning - won't tick over at all now! Getting a lift into work[]

Interesting points:
When cold, the engine fan starts - isn't this engine-temperature related? (suggesting engine thinks it is hot)
I've put RON 97 fuel in. Initially 50:50 and now pure.

Dave Wilkins suggests a dirty ISV valve (I'm new to the 964 mechanics so I'll have to google this)- this kind of stacks up with how it has deteriorated, but previous owner has never messed with the mechanics, apparently.

Any more ideas beyond Daves or similar experiences?

(Also for a newbie, which is the technical manual to show how to change / identify these things).

 

[Dave Wilkinson]

Lee,

I'll expand a little on my previous comment. The ISV is the Idle Stabilisation Valve - a little cylindrical gizmo on the very top of the induction system. It's an electronically controlled (by the DME) valve which s used to allow a controlled volume of air into the induction at idle in order to maintain the 800 +/- rpm idle speed. A common problem is that an overfill of oil causes oil mist to be vented to the induction and gathers in the ISV. This makes the ISV "sticky" such that the DME can't control it accurately - hence the problem with idling.

The solution is usually to clean the ISV with some carb cleaner or the like and re-install. In rare cases it may be necessary to perform what is called a "System Adaptation" using a Bosch "Hammer" tester. This re-aligns the DME settings for the ISV to correctly set the idle speed.

Hope that helps.

Regards

Dave

BTW, I assume by "Engine Fan" you mean the rear blower?? This is not only related to engine temperature (and very rarely gets used for this purpose) but is also part of the heating system for the cabin. If the dash temperature selector is a few points away from the blue dot the rear blower will come on to provide forced air to the mixing chamber ahead of the dash. This will happen even if the cabin blowers are not on (even though they ARE on, even at the 0 setting).

 

[Steve Brookes]

A word of warning. When cleaning the ISV DON'T poke inside with a screw driver to test the flap operation. Just clean it as Dave suggests.

 

[C2dweller]

Many thanks for your advice.

Yes - the heater may be set high as I got cold on the way back. This is probably the reason for the fan noise.

I have some carb cleaner, so I'll have a look at doing this (my wifes Ford Puma needs the MAF sensor cleaning very regularly so I'm used to this). On our other car I assume its due to the excessive wear in the engine - I'm feeling a bit down as it sounds like its the same for the 'new' car. Am I jumping to the wrong conclusion? It fits in with the way it gets worse when I drive it hard (assuming its exhaust gasses getting back through to the inlet area).

I'm still keen to know of some good manuals for this car - I don't think I'll try it until I know what springs are ready to launch out at me []

 

[Steve Brookes]

No need to jump to conclusions yet.....these cars take a while to learn their idiosynchracies. There are plenty with big mileages that are showing no sign of wearing out. Does this thread sound similar to your problems?

http://www.porscheclubgbforum.com/tm.asp?m=520475&mpage=1&key=&#522037

If so, you'll see at the end that it was solved by a simple DME reset (easily done on a C2 by a battery disconnect). The other thing to look out for with hot engine problems is a vacuum leak. It's worth checking round and tweaking up all the hose clamps on the inlet.

p.s. Mrs B used to have a Puma....only a 1.4....but one of the most fun cars I've ever driven....I used to often nick it off her! []

 

[C2dweller]

OK an update - cleaned the ISV (condition = quite mucky on the inlet side but spotless on the outlet side).

Started the car and the tick-over was fine.
Took it out for a quick spin ~ about 5 miles of country lane driving.
Started off fine but got worse as engine warmed up.
Stalled once during a down change near the end. By the time I got back onto the drive it wouldn't tick over again []

Happiness to sadness in less than 15 mins!

I am going to look into the ECU reset (- probably worth noting that the battery went flat twice over the past couple of days).

 

[RSGulp]

Try the 'intake system leak fix' on this thread. It's under 'smooooth running RS'. This is nearly always my first suggestion when people have idling/stalling issues. If you have an intake side air-leak your engine won't run smoothly at all. I'm guessing as your engine warms-up after 15mins, the rubber hoses are becoming more flexible (looser) and any small leaks are becoming bigger...

http://www.porscheclubgbforum.com/tm.asp?m=329251

And it's FREE so worth a try anyway.

 

[C2dweller]

Thanks - nice thing to try tomorrow.

I'm ashamed to say that I didn't refit new clips on the pipes so this could be the answer. The pipes seemed a tight fit without them so I decided to leave them off ...

PS I'm in Dumbleton near Evesham, you can't be far away in Gloucester - whereabouts are you?

 

[RSGulp]

I'm in Cheltenham. Drop me an email via my profile and let's meet up and kick tyres.

In fact, I'm 'working from home' tomorrow. I could drive over with the RS if you're in during the day?

 

[C2dweller]

Tried pinching up the screws half a turn and still no chance of ticking over when warm []

I haven't removed the air filter or air flow sensor, so that will be my next area to tackle.

(I've a also secured the ISV hoses on the input and output with a jubilee clip - so no leaks here)

BTW (1) is there any chance of this being due to RON 97 fuel? I filled 50:50 with RON 95 & 97. It only seemed to get worse as the tank got low and got worse still when I filled up from empty with just RON 97.

BTW (2) is the ECU reset for real? - maximum revs in gears...

 

[C2dweller]

Removed whole intake and cleaned air flow sensor.

Spotted a dubious join on engine side of air flow sensor (just tightened this up more during refit) and also pinched up the pipes on the ISV.

Took the car out for about 15 miles - now running mighty fine.

Thanks RSGULP, Steve and Dave []

 

[C2dweller]

Oh dear, spoke too soon.

Another 50 miles on and its got slowly worse and we're back to stalling again[]

I spoke with the guy who inspected the car for me when I bought it and he suggested getting a new ISV. He thought cleaning it wasn't really going to do the trick (he thinks the major contributor is a lack of use ). I'm puzzled becuase it seems to be OK for a while and then gets worse.

The previous owner only covered a few hundred miles a year in each of the the past 5 years, so I can see why it might be poorly if lack of use is a potential cause. There were no signs of it ever having been touched before me, so I don't think its been a pesistent problem before.

Any new ideas - better cleaning (I immerse it in 2cm of cleaner and give it a real good spray) or go with the new one? Could it be that the ISV is getting clogged because a vent pipe is blocked?

Lee

 

[RSGulp]

Hi Lee,

I'm going to throw a few more thoughts on the table - some things worth checking which could cause the symptoms you have. It's a difficult one though as it only seems to be intermittent or when the engine is hot/been running for up to an hour. Without plugging it into OBD it's difficult to tell exactly what's happening.

1. How is your oil level? (You probably already know but check the oil level using the dipstick, with the engine fully warmed up and engine running at idle and car standing on level ground.) If the oil is overfilled it can find it's way via the breather pipe into the ISV and might be fouling it up again?

2. Check the connection to the O2 sensor on top up the catalytic converter. Also check it is tight in the cat and hasn't worked loose. A bad O2 sensor or connection can cause poor running issues.

3. You could have an intermittently bad DME Relay. I have a good spare if you want to borrow mine, or you can order from any Porsche specialist for around £20. It's worth having a spare anyway as they don't last forever and if it goes completely it can leave you stranded.

4. Coils... let's see how you go with the above before we go here. []

Good luck!
Rich

 

[Steve Brookes]

To add to Rich's list:

5. Is the oil cap tight and the dip stick pushed fully home? Air getting in can cause idle problems.

6. There's a microswitch that the throttle (engine end) has to rest against when warm on tickover. Is it making contact?

 

[C2dweller]

Just got 'er started so I could check the oil and its now running fine [8|]

Started OK, - difficult to get out of the garage as it wouldn't tick-over. Once out I held it at a steady 1500 rpm and gingerly let go of the throttle and it ticked over OK.

Let it tick over for a while - about 10 mins and now its fine. Took it for a 15 mile drive and still fine???

With regard to checking the oil - how hard is this? I've used the gauge in the car until now and it sometimes reads ok and other times not. When ticking over at one point it read 'middle' and a few mins later - in the red - no car movements between readings. Tried using the dipstick and I can't be sure there's oil on it. It looks dry on one face and slightly wet on the otherside. It doesn't help that the oil seems very clean (although I'm not complaining). On the wet side it seems to be upto the high cork-screw part, which is over the max.

More headscratching ... whilst out for a spin, the normally rocket-high oil pressure (~ above 5) seemed to be sitting between 4 and 5 under load. Oil temperature when moving also seems to be below the middle range, but when ticking over on the drive it got to a happy middle of scale. All normal?

These are probably all normal things to a 964 owner, but they're certainly giving me the heebie geebies.

PS Thanks for latest advice - I really do appreciate it.

 

[Steve Brookes]

ORIGINAL: C2dweller


With regard to checking the oil - how hard is this? I've used the gauge in the car until now and it sometimes reads ok and other times not. When ticking over at one point it read 'middle' and a few mins later - in the red - no car movements between readings. Tried using the dipstick and I can't be sure there's oil on it. It looks dry on one face and slightly wet on the otherside. It doesn't help that the oil seems very clean (although I'm not complaining). On the wet side it seems to be upto the high cork-screw part, which is over the max.

More headscratching ... whilst out for a spin, the normally rocket-high oil pressure (~ above 5) seemed to be sitting between 4 and 5 under load. Oil temperature when moving also seems to be below the middle range, but when ticking over on the drive it got to a happy middle of scale. All normal?

Oil pressure when the car is warm and under load is fine if it's between 4 and 5. It sits closer to 5 while still not quite warm. And will be at 5 when revs are at the red line [].

Oil level can only be read properly by the guage or the dipstick when fully warm which means the thermostat has opened. In my experience the engine needs to have been running for at least 20 minutes to get to the right temperature. You can only get correct readings on both when the car is idling on level ground. Stopped at traffic lights is the ideal time to glance at the gauge. Sounds like yours is OK to me.

 

[kevin]

Not sure how much has been covered, so my tuppenth worth.

ISV cleaned and ok.
Idle microswitch, check continuity.
Headlamp adjusters, have been known to leak, causing idling issues with vaccum leaks.
Battery problems, is is a good one? or under too much alternator load
Fuel tank venting, or carbon cannistor, if the flow and return aren't good fuel starvation can occur, check when full, halfway etc, and release the fuel cap, it should'nt vent much if at all, and look at the fuel tank to see if its been sucked in a tad.
check dizzy caps and rotors.

kevin

 

[C2dweller]

So a great afternoon out and it ran like a dream ... until returning home. It doesn't like pulling back on the drive!!!

Stalled as I pulled on the drive and didn't really want to start again without some persuation.

Numerous stop / starts didn't cause any problem during the journey.

Some new things to answer from Kevin:
Checked idle microswitch - there appears to be a nice click
Battery problems - did have, but now have a brand new one - thanks Mr Bosch
Headlamp adjusters & dizzy cap - not looked at yet.

Thanks all.

 

[C2dweller]

Car hadn't had technical bulletin 9005 implemented, so I've implemented the modification this evening. Fingers crossed for tomorrow. This is the tie-wrap of the cable to the air flow meter (Have other people checked this is done to theirs?)

 

[RSGulp]

ORIGINAL: C2dweller

Car hadn't had technical bulletin 9005 implemented, so I've implemented the modification this evening. Fingers crossed for tomorrow. This is the tie-wrap of the cable to the air flow meter (Have other people checked this is done to theirs?)

Christ Lee, you're doing your Google research! []