ogm

I've just purchased a 1990 Carrera 4. The car has not been in use for a year.
So far i've done 1200 km and have noticed 2 problems:

On a few occasions the engine will not idle and stalls when i stop for traffic lights.
When I try to start it i must use the throttle to make it start, if i try to let it idle it revs from 1500 down to almost zero up and down and stalls before the pedal is fully released. This is with working temperature engine. The after a while its OK again.

Another problem is the last 2 times i've filled petrol, there is a lot of vacuum in the fuel tank when i open the cap. After the tank is filled and i drive away the engine hesitates when accelrating from 2000 revs. If i change down and open full throttle, the engine cleans up and everything is OK again. This seems only to happen after refueling.

The engine has a FVD 300HP performance kit and cup pipes.

Any suggestions?

Please advice.

Odd Gunnar Moe
Norway

JasonAndreas

The first thing you might want to try is to clean the ISV with carb-cleaner.

Then work your way to the DME relay, temporarily (to test warm starting) put a jumper inplace to confirm its failing or just replace it... An intermittent hot start issue is lot of times caused by failing solder joints in the relay.

But a failure of the carbon canister or the tank venting valve could be the cause both of your problems. On the top of the intake manifold, dead center the first black plug connector you'll find is for the tank venting valve switch. With the engine turned off you can apply power (from a 9v battery, etc.) and you should hear a click/pulse. The actual valve is on the back left side of the engine and the canister is in front of the left rear wheel well. To actually test the signal from the DME control unit I think you will need an oscilliscope?

KirkF

If you have access to a bosche hammer, you can actuate the tank vent valve to test it.

Kirk

ogm

Thanx !
I'will check the things mentioned. I dont have access to a Bosch Hammer, but i have considered buying an interface and download a diagnostic software to be able to check things with my laptop connected to the Motronic system.

Odd G

Red rooster

OGM,
Following on from Andreas , I had the carbon canister vent pipe block . Thats the pipe that comes from the bottom of the canister down into the LH rocker panel.
Happened quick and took out the gas tank !! BIG evacuation. Might be worth a quick look ?

Good luck

Geoff

Red rooster

Jason,
A thousand apologies !! Should have read " following on from Jason --- "

Put it down to trying to work and look at rennlist at the same time !!!

Back to work !

All the best

Geoff

rjohn@vt

I had the same prolem and tried the DMV relay and cleaned the ISV valve to no avail. It turned out to be one of the coils.

ogm

Cleaned the ISV. It had the original type clamps so I guess its the original from new. It wasnt very dirty but i cleaned it properly with carb cleaner. Tok off the FVD KN-filter and AFM. It was as new inside. Then went to the canister vent-hose. As the original air-filter box is removed, the outlet just vent under the body/door about half a meter long. It was blocked. Mounted a new hose. Befaore I started work i disconnected the battery to reset the DME. Took it for a 20 minute drive.
It was as smooth as it never have been. Guess everything is OK.

Thank you guys!



Odd Gunnar Moe
Arctic Circle
Norway

ogm

Checked for vacuum in the fuel-tank today. And it was totaly equalized to normal atmospheric pressure. No problems yet with the idle. The only problem i've noticed is if someone not used to the car stalls it when releasing the clutch from stand-still (not enough throttle or not used to the Porsche-clutch).
It will then not easy start without throttle. If some throttle is used it will clean up.
Is this normal because of rich mixture left in the inlet ports/cylinder or is it a sign of something not in order?


Odd Gunnar Moe
Norway

JasonAndreas

The ISV might still be gummed up a little. It might look clean but the real test is if the internal valve moves freely.

ogm

Do you say that i should be able to move some of the internal ISV parts freely?
Through the stubs for the hoses I see what looks like a metal flap.
Tried carefully to move some of the internal parts but it wasnt possible.

Regards

Odd Gunnar Moe

dfinnegan

The piece on the inside which is mostly closing off the opening in this pic should move . . .to the left in this pic, if I recall correctly.

I think credits on the pic go to Jason; I'm not sure. Not me, at any rate. Many thanks to those who post pics. I find them invaluable!

dfinnegan

By the way, if you hold the ISV between the two palms of your flat, open hands you should be able to roll it back in forth in a rapid fashion and the piece inside should move back and forth with a bit of a click as it hits the ends of its travel.

ogm

Guess I have to take it off again, clean it further. Can I test the valve function with a 9V battery? I understand that the middle connector is - and the outer ones is both +, depending on which way you want the valve to move?


Odd Gunnar Moe

ogm

Took off the ISV and tested it with a 9V battery. It operated fine.
Was also able to move the valve manually, i had tried to move it the wrong way earlier. It seems to have an internal spring that returns it to default position.

The distributor has been converted with a hose venting it. The venting for the rear lights is removed . Can I put on an Y-connector and vent the rear lights from the same stub or will i need a separate hose for the rear lights?

Odd Gunnar Moe
Norway