Porsche Enthusiasts Club Forum

This is starting to annoy me now, so I will hope to have a look this weekend, but thought I'd voice it on here first to see if any one has experienced similar issues.

When I first bought my S it suffered a little with a poor cold idle, it would often try to stall at idle (and sometimes did) and overrun felt excessive (i.e. felt like there was excessive engine braking). I removed all inlet components, cleaned, checked and adjusted the ISV, TB/plenum & AFM and replaced a few of the vac elbows that could not be got to once the plenum was back in place - also cleaned out and replaced the seals for the AOS. After that, the stalling issue was gone, but the idle was still not quite right. Maybe it was like this before, but I can't remember as keeping it from stalling was the immediate issue rather than a rock steady idle.

Now, fast forwarding a few months to the warmer weather, and it feels like it is gradually running a little worse. Feels and smells rich. Plugs have been replaced (old ones looked normal colour - no excessive sooting) and leads swapped, but still the same.

Here are my symptoms:
Idle - on the rev counter it can be seen to be hunting a tiny bit, but more noticeable watching the engine, it looks like it has a tiny miss every now & then.
Low revs & part throttle it often bogs down a bit. It feels better on a cool evening than a warm day.
Exhaust fumes smell rich, but the exhaust is not getting noticeably sooty.
It has a very distinct stumble at 2250rpm at constant throttle, causes car to surge. Not noticed as you accelerate through this rev range though.
At full throttle the car is a bit flat until you hit 4k (normal for an S?), then pulls well, but then bogs again at around 5k, before picking up again (I don't remember it doing this when I first got it)
Last tank of part dual carriageway, and part town driving gave 21.5 mpg. When I first got the car I was getting more like high 20's and that was in the winter.

I have checked the AFM operation, and that is nice and linear, inlet air temp sensor was also within spec. I checked the ECU temp sensor and when cold it was reading the correct resistance, although I have not yet checked it when hot.

I plan to double check the ECU temp sensor this weekend, check fuel pressure and grounds. The battery meter only ever shows as high as 13V, but should it not show charging voltage when running?

Is there anything else anyone can suggest checking out? Can any other S owners concur with how my car sounds/feels like it is driving? I can deal with it being a bit flat 'off cam' but at the moment, just pulling out a junction will cause it to bog down and stutter, which can't be right!

I plan to get it onto a CO meter as soon as I can, at the last MOT (December), CO was very low , HC low also.

Any suggestions would be very helpful

Change the sensor for the ECU they are nice and cheap same as land rover discovery

Not sure if the S has a hall sensor or not but if it has check the plug and socket known to crack with age and the connector pins fall out

Hi Waylander, I must admit, just replacing the coolant temp sensor had crossed my mind - just so I know it's out of tje equation, even though it checked out ok when cold.

Do you mean the hall effect sensor for camshaft? If so, yes, I think the S has one, I will check it out

if you search the bay for ERR2081 that's the same sensor as the bosch one

Sorry, I missed this, but found a Bosch one for £10 so happy with that!

With sensors I would almost always go for a branded sensor over an aftermarket one. Maybe I have been unlucky in the past (ABS sensors for example which have failed straight out of the box).

This one was listed as a Bosch one, but if it turns out to be an alternative then I'll be sending it back!

the last one of these I got " ERR2081" was a Bosch one with the correct Bosch number on it for £4.99 free post.

ERR2081 is the landrover part number not intermotor or some such rubbish

bosch number 0 280 130 026

Well, I tried a new dme temp sensor and no change (to idle at least, I have not driven it since). Checked the old one at a few different temperatures from 20'c to boiling and it was still within spec, just a few degrees out across the scale.

I then got side tracked investigating a top end rattle, which I think was just me being a bit paranoid as I found nothing jntoward and when I started up again today it didn't sound as bad. Suspect it was just usual cold start sounds!! I was worried it was coming from the tensioner, but all looked ok.

Anyway, while I was there I pulled the plugs to make turning the engine over easier whilst i was checking the cam tensioner and sprockets, and they are perfect colour, just a light sandy colour, no deposits. So maybe it's not running rich - perhaps it is poor ignition. It certainly smells rich from the exhaust and stumbles a little as if rich, but I'm no further forward! Will double check fpr anyway.

I know the engine mounts need doing as the exhaust almost touches the steering shaft, so wonder if these are contributing to the rough idle.

I had bench tested the isv before and was fine, when I unplug it the idle changes a little but is no better or worse. When I plug it back in you can hear a rushing of air noise, but suspect this is normal and amplified by the plenum?

Been thinking about this again this morning, the plug colour tells me that the mixture must be pretty good - exhaust might smell a little rich, but if it was excessively rich I would have sooty plugs, sooty exhaust and maybe some backfiring, etc.

Something I have not thought about, but will look into is the cam timing, possible that when the belt was last changed the adjustable rotor was not locked into place correctly, or has been misadjusted before. I have read the service manual method of checking inlet cam timing, but need to re-read as the first time it wasn't that clear. Suppose, first thing would be to just ideal where it is within the adjustement window.

Well, a little while after I started this thread I gave the car a good run, and tbh, it felt fine. A little off colour low down, but I think all S's are a bit like that.

Then I had a feeling a rear brake was dragging, a warm wheel confirmed that, then it locking up completely really confirmed it!!

Since I have rebuilt the rear calipers it makes the car feel a lot better free rolling, at low speed, etc.

Nevertheless, I went over to see a mate today and tried plugging in my car with the diagnostic lead I made up. The lead works OK, it reported one unknown fault which cleared and didn't return, but for some reason in the 944 menu, the system adaptation was not available. Some 964's had the same ECU, so selected that from the menu and could now see various sensor inputs, etc - all looked OK. System adaptation was an option now, but when we tried it, it came up with an error.

Seems the only way I will get it to work is with a Bosch Hammer. We put a CO probe up the exhaust and it was sitting between 1 - 1.5%, so again, nothing to worry about.

Gave the car a good run on the way home (with the roof out no doubt), and she felt really good - these 2.5 16v's just need winding up a bit!! I was probably worrying about nothing, lol!! I can be a bit picky at times, lol!!

I may well check the cam timing one day though, when I get some time - just to see if anything can be gained.