924Board.org

555mk555 · Posted: Tue May 08, 2012 3:07 am Post subject: rough idle and misfire

Hey cool cats...

ok, so I took my 924, 82 to get my manifold gaskets replaced.
She was idling rough and seemed to only be fireing on 2 cylinders.

The chap at the exhaust place called me to pick her up yesterday and I noticed she was still ideling rough (obviously not as bad) and she was still misfireing.

I checked all of the spark-plugs and leads and they seem fine... correct rotation and connection... still... mis-fire and rough idle...

I'm thinking there;s an air-leak, but I've not been able to put my finger/ear on it yet..

Has anyone got any thoughts on this>?

Thanks a million.

Michael

sciroccosteve · Joined: 16 Apr 2012 Posts: 215 Location: Rochester, NY

This is how I would approach it:
1-cracked/unplugged vacuum lines/intake boot
2-dirty fuel filter/lines/injectors
3-Incorrect idle setting --->
4-Air/Fuel ratio
5-incorrect fuel pump pressure/voltage

Also: check all of your grounds.
_________________
1979 924
2000 V6 Passat
"Let the fools have their tar tar sauce."
C. Montgomery Burns

555mk555 · Posted: Tue May 08, 2012 7:50 am Post subject:

Hey sciroccosteve

thanks for that.. I had a torn intake hose a few months back.. I'll start her tomo and make sure to hold hoses in place etc. check for a leak there.

I had to get my coil/ignition rewired last month as well.. I'm not sure how the chap did it, but I'm worried the sparks might not get sufficient amount of power... could that be why she's only firing on 2 cylinders?

will get back to you if I have any other findings.

Mick

!tom · Posted: Tue May 08, 2012 8:10 am Post subject:

You could have the plug wires on the wrong way 'round. Double check the firing order, distributor rotation direction, etc.
_________________
78 924 NA
5-lug

sciroccosteve · Joined: 16 Apr 2012 Posts: 215 Location: Rochester, NY

555mk555 · Posted: Tue May 08, 2012 6:57 pm Post subject:

I'm heading out there now...
It must be 2 issues... as I cannot imagine such heavy engine shake/rough idling just because of a misfire...

will keep you all posted.

thanks again,
M

555mk555 · Posted: Wed May 09, 2012 1:26 am Post subject:

ok.. so it seems that all air hoses are fitted correctly...

I noticed that after start-up and turning off of car again produced a humming sound... like a switch/gauge making a noise similar to that you can make with a wine-glass when running your finger over it...

I've heard this noise before, but always disregarded it...

anyway, I traced it back to being pretty much next to the throttle body... that's also where a switch is fitted, which seems to be connected via another switch on the engine, just on the other side of the ignition coil to where the throttle body is...

WHAT IS THIS SWITCH? is it the air/compression sensor?

It looks pretty shot...

bottom line is, I still seem to be misfiring and I'm def idling far too heavy... the car almost rocks... I don't think it's my engine struts... btw,.

Any other thoughts are very appreciated.

Michael[/img]

555mk555 · Posted: Thu May 10, 2012 1:35 am Post subject:

Ok, the noise/alarm humming sound.

This has sounded again, but now with a more distinctive start stop, start stop, until fully rung out. I have determined that it's in fact coming from what I think is the: AIR FLOW METER.... could this be?

It's situated below the coil and to the left of the throttle body...(underneath)

Does this have a 'sounder' that produces the buzzing alarm like signal?

If the AFM is not working correctly, would this influence the IDLE of the car, as well as MISFIRE? or would you put your money on saying it would be 2 different issues that I'm being face with?

Hope someone can help me find reason....

Warm regards from a 924 owner who misses his car on the road....

Ozzie · Posted: Thu May 10, 2012 7:30 am Post subject:

Are you sure its not an injector leaking?
Some are very noisy.

Could be a faulty WUR, CSV. Fuel pressure leak is the most likely cause in that area.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

555mk555 · Posted: Thu May 10, 2012 8:43 am Post subject:

i dont know about the sound being produced by a leaking injector.. Way too consistent pattern. i cant find anything online about a component under the 924 hood having a warning sounder fitted. im going to check for air leaks again... Will keep u posted, thanks for input.

555mk555 · Posted: Fri May 11, 2012 2:41 am Post subject:

RESULT

way flippin ayyyyyy!!!

because she had been standing a while I'm guessing, one of the pistons must have been dried up...

I poured some SHIELD fuel injector cleaner in with my petrol... I used the one that also cleanses the air intake etc.

she started to idle much better right away... AND then.... I noticed the exhaust puffing out a few cloudy breaths of smoke, where the s*it was obviously burnt away....

I took her for a quick turn around the neighbourhood and BOOOOOOM she sounds amazing... changing of the manifold gaskets def making a huge impact. Great idle... no negative vibrations and a clean healthy run and sound....

I'm amazed....

thanks for all your input...

I'm heading for a nice ride into Cape Town this eve... way hey!