Help! Pop Idle...

Dades

Was mucking bout with the 'new' 924 over the weekend.

Sucessfully installed a new (old) wiper motor and fixed my wipers issues on Saturday.

On Sunday I decided to install a "hot start" switch to temp solve an affliction of many 924s in starting when 'warm'. This involves installing a manual earth switch that tells the Cold Start Valve to give a squirt of juice.

I must have squirted a bit much because on startup from warm I popped the rubber air dome cover thing in the engine bay off (was loose it seems) and had to reseal and tighten it.

I disconnected the manual switch and the car starts and drives as before - but now my idle is fooked. It runs lumpy for half a minute and then cuts out.

Help!

alias no.9

I don't know the engine, is it carb or injection? Could there be an air leak at that rubber dome, is it before or after the carb/injectors in the intake manifold?

Dades

Hey alias,

It's an injection system.
I thought I'd visually checked for air leaks, but it's definitely worth looking again (when I'm home from work).

The part marked is the part that popped out:


Anything else worth putting on the checklist?

mustang68

Check the pipe again, it may have cracked, I believe that you can use a blowtorch (off of course!) and run it along the pipe and see if the revs pick up.

If there are no leaks check that you didn't disconnect the MAF, idle control or something similar.

Good Luck

Dades

I've heard of that blowtorch trick and don't think I'd be comfortable even if I had one.

Had another quick look this evening. Nothing seems to be disconnected, and the idle seems a bit better than yesterday - just very low still. I'm still waiting for my Haynes to be delivered btw!

gn3dr

Well teh K-Jetronic works with a plunger regulating fuel pressure when it is moved. It is moved by the air flow into the engine pushing on a kind of dish shaped disc attached to the plunger. So if you had some kind of backfire that blew that chamber off then it's possible it also bent something in the plunger system....Might be worth looking at.

I do have to ask though, not knowing Porshces and this hot start "fix" - why adding more fuel makes teh car easier to start when it is hot. I would have thought adding more fuel in this state would only cause it to be too rich and harder to start. Is this a recognised workaround from a reputable source or is it one of those "internet fixes":rolleyes:

Dades

gn3dr wrote: »

Well teh K-Jetronic works with a plunger regulating fuel pressure when it is moved. It is moved by the air flow into the engine pushing on a kind of dish shaped disc attached to the plunger. So if you had some kind of backfire that blew that chamber off then it's possible it also bent something in the plunger system....Might be worth looking at.

Thanks, gn3dr - I will look into that idea. Still missing my Haynes though!

You rightly point out that the "hot start" fix sounds flawed. It's the name that's wrong in fact (annoyingly so). Although known as the hot start fix the fix is to solve probems starting the car from "slightly warm" in fact. That is, perfect start from cold and hot, just not from when the car has been sitting for maybe an hour. More here if anyone interested.

ikillcopiers

A handy hint, any Porsche related go here

http://www.porscheclubgbforum.com/

You don't have to be a member to join the forum, and
these guys know *everything* about these cars.

The 924 and 944 forum are very active, and if you put
up a question you will always get an answer.

I'm not too hot on the 924 (I have a 944 Turbo), so I
ain't gonna guess when I know those guys *know*.

Another person you can ask is Donal (AKA VanHireBoys).
What that man doesn't know about 924/944's.....

Dades

Thanks for the tip! I'm on another 924 forum but never came across that one.

ikillcopiers wrote: »

Another person you can ask is Donal (AKA VanHireBoys).
What that man doesn't know about 924/944's.....

Donal nearly made it to my house last weekend for a nose about.
My loss he didn't - though that was Saturday and I only make a bollix of things on Sunday.

MercMad

That set up is very similar to some of the Mercs, through the 60's. The early Pagoda suffered from poor warm starting and there were actually 3 different modifications to try to sort it.Modifications to the Thermo Time switch, extra relays & solenoids.

Anyway you may have damaged the plunger indeed, and you may also have popped off another vacuum pipe further along.I have also found that if these cars become slightly, or remotely flooded, they will not idle cleanly or rev out the way they should.

No amount of cleaning plugs, or "Italian tune ups" will help.Only changing the plugs will sort it.

Also the idea of the extra squirt is actually not intended to richen the mixture, as is required for cold start, but purely to actually GET cold fuel into the combustion chamber.Alot of cars when warm can suffer from injector leak back or vapourisation meaning they get difficult to start when hot.

Just for future reference, even when cold the electronic system give a fine mist for about 0.3-0.8 seconds therefore you need to be pretty swift with your button. I have come across folk who think they need to keep it pressed 'till it start !

Best practice is to spin the starter and flash the button and floor it.

Dades

MercMad wrote: »

Anyway you may have damaged the plunger indeed, and you may also have popped off another vacuum pipe further along.I have also found that if these cars become slightly, or remotely flooded, they will not idle cleanly or rev out the way they should.

No amount of cleaning plugs, or "Italian tune ups" will help.Only changing the plugs will sort it.

The sparkys? I pulled one and it looked fine. Why would these need replacing?

And thanks for the electronic starter tips MercMad. I guess using a spare "toggle switch" I found lying about wasn't such a good idea. Off to Maplins tomorrow for a push button!

Can't really do much else till I get the manual though. I'll have to live with the low idle in the interim though I'm hoping it might fix itself. :pac:

MercMad

Yeah the spark plugs. They canb look perfect but if they have ecver been flooded they will never be 100% again, that goes for a lot of modern cars too. In the old days you could heat them and they'd be fine, but that ruins their heat range.

The Thermo Time switches suffer from increased resistance which reduces their performance.

VanhireBoys

All 924s are difficult to start when they are heated up - its a well known flaw...!

What I suspect is that the "domed cover" or metering head pipe has suffered a crack and is letting in air. There are 2 particular rubber hoses and these are famous for this issue. Even the slightest pin hole will cause problems...Quick fix is loads of gaffer tape.

Also look at all the rubber hoses around the manifold. There is an idle stabilisation valve as well which has a small hole in it to boost the revs when cold. As the engine heats this closes...!

I am kicking myself for not making it on saturday now .. I would hve put you off that hot start switch....!

Dades

LIGHTNING wrote: »

I also just bought another 924 it will be waiting for me wheni get home from the states.

Sweet! We'll await the pics.

@MercMad - did not know that about sparkys. Will pick up a new set and try and put them in at some stage. The others can serve as spares anyway.

On Tuesday I adjusted the idle on the throttle body, and this seems to have solved my initial problem anyway. Not gonna try anything else till I get my Haynes.

VanhireBoys wrote: »

What I suspect is that the "domed cover" or metering head pipe has suffered a crack and is letting in air. There are 2 particular rubber hoses and these are famous for this issue. Even the slightest pin hole will cause problems...Quick fix is loads of gaffer tape.

Also look at all the rubber hoses around the manifold. There is an idle stabilisation valve as well which has a small hole in it to boost the revs when cold. As the engine heats this closes...!

Will treble check for any cracks etc.

VanhireBoys wrote: »

I am kicking myself for not making it on saturday now .. I would hve put you off that hot start switch....!

I'll only be put off it if the warm start can be fixed. It's feckin embarrassing to show people your car, tell them how fantastic it is, and then sit cranking it for 10 looong seconds!



This is going in unless you have another solution!

ikillcopiers

LIGHTNING wrote: »

... from what I saw the dash isn't cracked!

Lucky, lucky you!

That'd be the first 924 I ever saw with a solid dash if that's the case,
even a pampered 924 Carrera GT I saw up North had a cracked dash!

Dades

LIGHTNING wrote: »

We should have a 924 meet when we get our cars running properly. My mate is picking up my 1980 black 924 next week. It has the beige pasha interior and from what I saw the dash isn't cracked!

Definitely up for a meet up. Is your 'new' car the 1980 black one in Cork that's been advertised for a while? Can't wait to get a look.

LIGHTNING wrote: »

My old car had everything earthed to help the cold start but I wouldn't recommend doing it. Excuse my grammer I'm posting on a phone

Would happily implement any solution to cure the warm start so if you have any other suggestions let's hear them!

I did read on a Porsche forum somewhere that installing the newest fuel pump from Porscheshop.co.uk (€145 + delivery) solved the problem for one owner. A possibility?

Dades

Installed my "warm start switch". A couple of times today was starting the car after it had sat for an hour or so: turns over - not firing - press the button - vroom!



There was already an unused round hole under the steering column handy.