_Thomas_

Hi

suddenly my 1984 Euro S2 (LH 2.2 jetronic) does not idle any more. The engine still runs ok above approximately 2000 rpm.
I checked the throttle switch and the Hot Wire Mass Airflow Meter (MAF), and I also checked the corresponding resistances and voltages on the 25-pin plug of the ECU.

If I unplug the MAF the engine does idle quite ok (emergency program?). Is it possible that only the part of the ECU which controls the idle is broken?
Are there any other tests I could do?
Regards
Thomas

Mrmerlin

sounds like MAF failure.
My 84 Euro did the same thing it would run OK above 2500 rpm but wouldnt idle,
a rebuilt MAF and she purrs

_Thomas_

Mrmerlin
Can you remember what was wrong with your MAF (what sort of failure)?



I did check the MAF as per JDS Porsche instructions

1. battery voltage between pin 2 and pin 4
2. sensor resistor is OK, between pins 3 and 5 reading approx. 4 ohms.
3. idle mixture pot is OK, between pins 3 and 6 reading 570 ohms.
4. MAF has an output voltage, 1.8 V at pin 7 of ECU

My MAF was recalibrated by JDS Porsche about 5 years ago (engine was running lean).
Is it worth opening the sealed plastic cover of the MAF to see inside whether something went (obviously) wrong?

tv

a vac leak will also mess with the idle

John Speake

Measure the tail pipe CO at idle..... shoild be 1-2%.

_Thomas_

Hi tv
> a vac leak will also mess with the idle
I agree but it would have to be huge and I couldn't hear anything when I was 'inside' the engine bay with the engine running, and I think I it is unlikely to develop suddenly; and I think rpm would still be quite stable with a vacuum leak, which it isn't.


Hi John
The tail pipe CO was checked to be 1 % only a short while ago (has to be done annually by MOT laws). Now I cannot measure it properly because it doesn't idle ...
The car hasn't gone out of tune gradually, it ran perfectly until yesterday morning. Something went wrong suddenly.

Forgot to write that with the MAF connected the idle rpm goes up and down until the engine dies, with the MAF disconnected the idle is stable.

John Speake

I think the idle mixture is now not correct, could be a ruptured diaphram in a FPR or damper (check vac lines to these). Or the MAF has suddenly gone wrong. I wouldn't recomend taking the black cover off...

When MAF is disconnected the LH ECU goes into limp home, with a fixed injectgor pulse size at lower rpm, then another larger pulse width if you can coax the rpm above about 3000rpm (from memory)

tv

I have an 85 S2 and when I forgot to tighten something down (creating a vac leak) I ended up with a hunting idle that wanted to stall otherwise drove sorta ok. All I can say is check the manual as it has a trouble shooting guide.

If not a vac leak this sounds electric/signal - which means MAF, either brain, or even that thing under the passenger side of the intake spider arms even. maybe even the wot switch. If you know anyone in the region with a working S2 you could swap the major bits in and out to see if that solves it. Wouldn't take long to rule out the 3 pricey items.

ralphr1780

Thomas,
As outlined by other fellow listers, symptoms of vacuum leak or malfunctionning MAF.
This link might be helpful:
http://jenniskens.livedsl.nl/Technic...5/MyTip596.htm

Good luck,
Ralph

Mrmerlin

Thomas you should remove the MAF and have it checked by a rebuilder, the chances are good it has gone out of spec,
the simple tests that you performed are not the same as the testing rig that a rebuilder has.
The 570 ohms that you measured should be closer to 380 for a fresh MAF

_Thomas_

I got a MAF reconditioned by John and with it the car runs again perfectly.

Thanks to everybody and Happy New Year!

Mrmerlin

Keep Em Flying!