dies on idle only after warm, 944s2

marko · 03-25-2004, 09:33 PM

Hey all,
Been reading threads and posts for 3 days now.....phew, going blind and maybe a little confused.
I think my problem is the Idle speed valve but I'm not so sure now.

My '90 S2 dies on idle only after it warms up and intermittantly. It seems to happen when a whinning noise is audible from the rear end (fuel pump). I checked the vacuum lines and found a huge break in the hose that snakes thru the manifold. The break is at the rear of the engine to a round thingy which I assume is the idle speed valve, the other end goes to the middle hose position on the throttle body. I changed the hose with a regular hose, the original hose had a strange little valve sticking out in the middle with a little spring inside, hope that doesn't matter too much. ( the porsche dealer in tampa doesn't have that hose on hand), anyway, that didn't fix the idle problem to my surprise. there is a lot of dirt and grim where the break occured and I thought after reading the posts that maybe some of the dirt got into the ISV and it needs to be cleaned. Looks like a hefty job and I'm not much of a mechanic, so I did some easy stuff like checking and cleaning the speed and temp sensor wires, but no luck. Then I read about the DME and how it should shut off the fuel pump when the key is on and the engine is not running in case of an accident , but my fuel pump turns on when the key is on and the engine is not running but only when the engine is warm. I guess that maybe the DME relay might be stuck in the on position for the fuel pump power on pins 4 and 9 but why only when the engine is warm? I'd check the fuel pump relay, but I can't find one!! do S2's have one? I thought maybe the fuel pressure regulator but what would that matter if the engine isn't running.
hmm, I just had a thought that maybe one of the sensors is telling the DME that the engine is running?

Any help would be GREATLY appreciated.

marko · 03-26-2004, 07:01 AM

OK, I found out from this site http://www.clarks-garage.com/shop-manual/fuel-05.htm that there is no FPR on 85.5 and up, I'll check the DME relay and make sure it's ok.

Makis · 03-26-2004, 08:07 AM

Quote:

Originally posted by marko
OK, I found out from this site http://www.clarks-garage.com/shop-manual/fuel-05.htm that there is no FPR on 85.5 and up, I'll check the DME relay and make sure it's ok.

There is a FPR on a S2.
To sort the out the idle problem you should make sure you don't have a vacuum leak before you go for the idle valve. Make sure you don't improvise with the vacuum pipes and use original pipes. You could try to use some carb cleaner while the engine is idling by feeding the carb cleaner after the air filter through the AFM. The carb cleaner could clean any rubish build up in the idle valve and could spare you the difficult task of actually removing the valve. If this does not help you may have to remove the whole intake manifold and that will be a bigger job. Removing the inlet manifold will give you the opportunity to check properly and replace where necessary all the vacuum pipes.
If the vacuum lines appear OK and you have no leak then inspect the operation of the AFM and O2 sensor both of these could cause IDLE problems.

marko · 03-26-2004, 09:44 AM

Oh, that sounds like a great idea! I'll try that next. I wasn't looking forward to taking off the manifold. Thanks.

I've checked the vacuum lines, but I can't say 100% sure that they're ok by looking at them. The non original vacuum hose is temporary til I can get a new one. (gosh, I hope that isn't my problem, there was a little valve on the origanal hose) I checked the DME relay and the solder joints, springs and contacts look ok, (I know, visual is not a great test for relays)

But about the FPR, are these site's wrong, or am I reading it wrong?

FROM:
http://www.clarks-garage.com/shop-manual/fuel-05.htm
"The DME relay which is used on 1985.5 and newer 944s is essentially the same as the fuel pump relay used on early 944s. The fuel pump relay on the early cars is located on the fuse / relay panel under the dash on the driver's side (LHD). The DME relay actually has two relays / contacts. The primary relay and contact provide power to the DME (and on turbocharged cars the KLR) control unit. It also provides power to actuate the secondary relay. The secondary relay provides power to the fuel pump "

FROM:
http://www.frwilk.com/944dme/

The DME relay is actually two relays in a single package. BOSCH refers to them as the main relay and the fuel pump relay.

I'm also thinking maybe I have two problems, the fuel pump running when the engine is shut off and the key on (when its warmed up), and the idle problem.

Thanks for your reply, I greatly appreciated it!!

marko · 03-26-2004, 07:31 PM

Hey Makis, I tried spraying a bunch of carb cleaner in the intake and reving and spraying and reving and spraying about 20 times but no luck, it still slowly dies on idle.

I did however find my 944 cd that I bought a long time ago. I thought it was usless for what I was doing about 3 years ago, but I was looking at the wrong volume, I checked out Vol. I-A and it has the stuff I need. Shows how to check all the control unit sensors and stuff, alot of them right from the control unit plug with a volt/ohm meter. Great stuff, also found a fuel pressure test with a trouble shooting FLOW CHART !!

Makis · 03-26-2004, 11:16 PM

Hi, Marko, The carb cleaner wil not do any harm it will clean the intake a bit. I just hope some of that cleaner find its way through to the idle valve air bypass circuits so it cleaned the valve a bit.
Yes if you have the manual you can test all the electrics/electronics that can affect idle and there are a lot of them. As I said on my list I would consider.
1. Vaccum leaks
2. AFM (air flow meter) both air temperature sensor and flow measurement, which at idle can be affected by a bad resistor track in the AFM.
3. O2 sensor. A faulty one would make the mixture too rich at IDLE and can have the engine STALL. Check spark plug colors to see if you running to rich a mixture.
4. Also you should check the Throttle position switch operation. At IDLE if the switch is not working or adjusted propery, the switch will not tell the DME to IDLE and the DME will not use IDLE fuel/air control. In this case the engine will stall, because the DME is nnot controlling air supply through the IDLE valve solenoid.

marko · 03-27-2004, 04:50 PM

Hey Makis, thanks again for your help.

It's hard for me to check all the vacuum lines without removing the manifold, but they all appear ok.

One thing that bothers me is that when my engine conks out after about 3 or 4 minutes after idling on a hot start, I hear the fuel pump operating. The DME relay is supposed to cut off the fuel pump when the engine isn't running. Oh, by the way, I saw gas coming out of the two black plastic caps on the head cover after one of the conk outs. I thought maybe too high a fuel pressure or a leaking fuel injector, but I always come back to the fuel pump running when the engine isn't. It just goes round and round in my head. ouch!! I also think about the original problem I saw of that broken hose I replaced, I still can't figure out what it's connected to. It doesn't go to the ISV like I thought, it goes to the back of the engine to a flat circular unit under the manifold on one end (that's where it broke) and the other end goes to the middle nipple on the AFM. The porsche dealer said the idle speed valve hose but I probably didn't explain it correctly.

I spent about 100 bucks on tools today and I'm gunna try and measure the fuel pressure, but I'll probably need a 11 X 1.5mm adapter thingy for the test connector and be stuck again for a few days.

I'm think I had a rich mixure before this problem started cuz I have black soot on my bumper all the time (but don't acually see any black smoke) so that might make it a little harder to trouble shoot. I also had the "trouble light" on for about two years...lol. I've just leaned that is due to an emission component being bad, I always thought it was because my air bag isn't working.

Thanks again for your input...

Makis · 03-27-2004, 11:23 PM

Hi Marko, I think I know which pipe you tried to fix. I don't know how you managed to do it because the inlet manifold is well in the way. I think the pipe your try to fix is a crank ventilation pipe between the engine block and the throttle body. The pipe comes from under the inlet through a purpose build hole in the inlet. If that pipe is leaking it will generate a huge vacuum leak which certainly will be the cause of your idle problem.

I would not be worried at the moment about fuel pressure or the fuel pump. To check the mixture try to have a look at the color of your spark plugs. If they black and wet then you are running rich. A vaccum leak can cause this condition at IDLE, but under load things should be OK.

How does the engine work under load. Have you got good power at the top end. Any imperfection here can give some clues.

marko · 03-28-2004, 12:28 AM

Yes, I have good power at the top end and good acceleration and it runs pretty smooth, just at a stop light it slowly starts to die, I have to punch the gas and try to keep the revs high or it will die, then it runs fine until another stop light. (guess I wouldn't have that problem in the UK eh? nothing but round abouts...lol.. I spent 2 years in Scotland, had a great time there)

Yes, that it is the hose that broke on me. It wasn't easy getting it out. The big problem is that it has a tiny valve in the middle, sort of a T connector with the valve on the end, I think it's a releif valve if the pressure gets to high. I taped the break, put it back and still had the problem, then replaced it with a regular hose with no valve. No change there either. Today I got the engine warm, then when it started to die, I removed the hose at the throttle end and the idle came back up, then started to die again after about 15 seconds, I plugged the hose, the idle came back up again, then died. So that may or may not be the problem, I dunno, but I can't get an original hose this weekend, so I'm trying different things.

I'll check the plugs in the morning. Also, still trying to figure out why the fuel pump is running when the key is on.

Makis · 03-28-2004, 01:25 AM

Good, to hear you have good power. This means that the vacuum leak is still likely to be your problem. The fuel pump operation is controlled by the DME software. If it is running there is a good reason for it. It is unlikely there is a bug in the software or the DME is faulty. If the DME was faulty the engine will not run at all. The reason is still running is because the DME still tries to keep the engine running, however once the engine has stalled the pump should eventually stop. If not it could just be a software fault but I cannot believe this. The only way the DME will keep the pump going will be if the DME thinks the engine is still running which means the speed/reference mark sender may send some signal even after the engine has stalled. Checking connectors to the various sensors and cleaning them may help.

On the pipe you want to replace with original one I can see it may be easy to replace but can't see the T connector you are talking about which must be under the inlet. Access to that would be impossible without removing the inlet manifold.

marko · 03-28-2004, 01:55 PM

Hey,
I checked the spark plugs and they are covered in black soot, alot. The plug near the front is the worst then gets a little better toward the back.

I put the orginal hose back in. I know it's not the way to do it, but I used electrical tape and duct tape on the outside, I'm sure it's sealed pretty good, til I get a new one anyway. still no change. I checked the engine temp sensor and air temp sensor and they read good. Each fuel injector reads 3 ohms.

Makis · 03-29-2004, 08:30 AM

It looks like you are running a rich mixture. You may have rich idle mixture or even rich mixture when the engine is nor idling.
O2 sensor could be the prime suspect here. Also the CAT may be clogged and the exhaust is not flowing properly. However if you had problems with the exhaust you would also notice performance problems, like the car is unable to reach the redline in second or third. Over rich mixture at idle will stall the engine eventually.

It also looks like you may have to check your ignition system in particular distributor cap, rotor, ignition wires.

You could get new spark plugs and see if the idle stalling problem disappears temporarily.

marko · 03-29-2004, 11:36 AM

Hey Makis,
I couldn't find an adapter for the fuel test so I gave up and took it to the shop. They just called me......the FPR and damper are bad, also two knock sensors.

They wanted $101 for each, so I'll look around myself for the parts, I'm sure I can find em cheaper.

Thanks for helping me with suggestions, I greatly appreciated it.