90' 944 s2 cab - idles rough

[Panic_1302]

I realize this might be a common problem, but from what I have read so far the issues involved with the rough idle are not like the car I am writing about...
The car isn't mine, but a good friends. She got it a couple months ago, and I must say it is quite a ride. The car has around 57 thousand miles on it, and its from the states. Its now in Canada, and it is a really nice car.

The only issues I can find are that it tends to idle rough if the fans have been running for a while after shutting it off, and it sometimes won't fire up. There is no loss of power (I can attest, I got it up to 80mph real fast when I probably shouldn't have).

My good friend is a little worried about this issue. I think it is her alternator, but I have a feeling that it might be something else, maybe fuel related.

If anyone here can help I would really appreciate it!

[gtgt__bangbang]

shot in the dark here , but there is an "idle stabilizer", which might not be stabilizing ...

looks like dis Porsche 944s 944S2 Idle Stabilizer Valve 0 280 140 514 | eBay

[Jfrahm]

It's pretty hard to tell on the internet what you men by "idles rough" but...

Of course you can start with basic troubleshooting. Check the ignition: cap, rotor, wires. Look for sparks in the dark. Check the plugs. Get it to idle rough and then disconnect one plug in turn to see if they all affect the idle the same. Check the plugs when it is acting up, is one clean or dirty or wet?

If all that checks out you can look for an intake leak. You might get one with a warm engine. If the plugs are wet or fouled that could also explain the hard restart. A weak spark could also cause this, you should make sure the spark can jump a 10mm gap. Sometimes the coil misbehaves when hot.

If all the plugs are the same and they are fouled/wet you might need plugs and an O2 sensor, but why not run through the checks and let us know how you get on?

-Joel.

[veleno]

How about just taking it to a dealer and having them check it out?

[gtgt__bangbang]

"take it to dealer" ... lol milk just shot out my nose. Not too bad but the cheerio taking the ride along hurt like hell.

I see that at least one person aint down with the DIY / advice pooling nature of this board. I suppose there are independent shops worth a visit with these cars, for those without the time skill or interest to fix it on their own, but the last thing I want to do with my own $10~15,000 car is make it hostage to a $1000 dealer bill. Simply the vibe given out if I go there to order a part is reason enough to stay away unless perhaps I want to have the nitrogen rotated in the tires of my $90,000 2 year old

[pi_]

A long shot - many years ago I had a Alfa Romeo that would not start when shut-off hot. I had to wait 30 minutes before it would start.

The car had a water heated aluminum inlet manifold that had become porous and was allowing hot water/steam into the inlet manifold when the cooling system was pressurized. Once cold the water injection stopped and the car would start. It also tended to stall at the bottom of a hill as I had run it a significant distance on closed throttle, hence maximum vacuum.

I realize that a 944 does not have a water heated inlet manifold, but is there another route for a pressurized cooling system to dump water into the intake system? The head gasket is a candidate but that would not be good news.

A cooling system pressure test should tell.

Probably not the first thing to try, but if all else fails...

Chris

[Jfrahm]

Sadly a dealer nowadays might have no idea how to do basic troubleshooting on a 1990 944S2 (which does have a water heated throttle body to prevent icing, FWIW.)

The good thing is that basic troubleshooting will probably give you some clues.

[Panic_1302]

Hey guys!
I made this post for a friend, she may log in with my account later to give you a better idea about the problem.
The car isn't mine, and she would go to a porsche guy first (mantis racing, up here in ontario), rather then the dealer.
That just seems too expensive!

I havn't had a go over it all the way yet, and I haven't seen the car in a while, but I would rather go the DIY way, I'm sure she would too.
Its basically a fancy AUDI engine anyways right? haha

[Panic_1302]

Hey guys, I'm the friend. Thank you all for your extensive input. It's my starter car and having fun learning about 944's. I will see how I can go about trying some of the things that were suggested. Also thanks for the humour gtgt_bangbang; even I know not to just "take it to the dealer" when charging $100/hr for my S2.

The idle is still hard when starting only if it's been run that same day. The new issue that's arose is the other day after driving her for about 5 minutes, once shut off key out of ignition the fan ran for a long time... 3 hrs to be exact so I had to disengage the battery. It was suggested I check the coolant (of course) which I have yet to do but will. I'm wondering if there's an issue with the alternator system as the voltage meter reads a little low on my car (12,12 1/2 volts).

And to add about the idle issue from previous, don't know if this makes a difference in diagnosing, but I had timing belt, balance belt, cam shafts, guides and water pump replaced when I got the car.

Thanks again folks. Fill me in if you have opinions/suggestions

[beamishnz]

Fan running on is common problem with late 944's. Very often it is the thermoswitch on the top left of the radiator. 3 pin one on an S2. The part is cheap and is an awkward but achievable DIY replacement from below. Straightforward but difficult to get to. Remove engine tray and access from below - you can get it out from above but very difficult to tighten it back in from above. You will need to top up and bleed coolant system afterwards and clear up coolant from all over the floor Allow gentle 1 - 2 hrs if you are a first timer. This is the part you need Porsche 924, 944 & 968 (1976-1995) - Switches, Motors, Relays, Fuses & Wiring - Page 6


Alternatively it can be the fan relay (large silver one at back of fuse box) ... that is expensive but easy to replace ... to test if it is the relay pull it out when the fans are running. If they keep running it is the relay. If they stop it is the thermoswitch. If it is the relay then get a used one or repair/resolder existing.

Clarkes garage has a good section on this.

Unlikely that this has anything to do with rough running but worth sorting this first.

Rough running is likely to be inlet air leak downside from MAF or possibly leads, plugs ... if the easy things don't work putting it into specialist for diagnostics even if you end up doing the work yourself. Otherwise you can spend a lot of time and $$ replacing parts not required.

Rough idle can also be engine mounts (OEM mounts are the ones to go for - aftermarket don't last) and they are all tired on these cars at this age ... but won't affect starting.

Unless you have evidence of recent replacement and the car is new to you, and you intend to keep it I'd be looking at engine mounts, belts, cam chain, cam chain tensioner kit, distributor cap and leads, rotor as a freshen up to keep you running nicely and safe for the next 30,000miles. Oh and do gearbox oil (Redline) and engine oil and air oil filters whilst your hands are dirty

Welcome to the world of 944's!

[Panic_1302]

Very useful information beamishnz, thank you! I hooked the battery back up fully charged fan went right back on. Pulled out fan relay, fan turned off. So if your diagnosis is correct it'll be thermoswitch. Finding the thermoswitch ain't easy however :s from up top anyway. I looked for it left of the radiator. Google wasn't much help. Il need a proper diagram so il keep searching.

[sausagehacker]

Correct me if I'm wrong, but doesn't the S2 have an additional temp sensor under the intake manifold? I thought I saw a thread recently about it - it's for air temp.

There are a few more sensors I would test (most can be tested with a multimeter, Clark's Garage has good info for many of them).

- TPS, because the idle switch may be on the way out
- Coolant temp sensor, because that factors into the fuel injection
- Air temp sensor I mentioned

The ISV (is it called that on the S2?) should be inspected as well. As Jfrahm mentioned, look for vacuum leaks.

beamishnz has a very good point about the motor mounts - they go out on our cars. Make sure you don't cheap on those if and when you replace them.

[beamishnz]

Yep the sensor is tricky to get to but not impossible. Find it from above but remove/replace it from below. It is right below the top radiator hose on the left hand side of the rad. (Left as you sit in the car - same side as the fuse box ) It will have a short cable leading to it. Wiggle the plug off the sensor and you will see a grey plastic 3 pin electrical terminal with a 30mm brass hex base. You will need to buy a 30mm deep reach socket to get it out. It is screwed into plastic radiator so low torque so you don't need to buy a posh brand. Just get the cheapest socket you can. You won't need a 30mm deep reach that often

If you can't find it, I will go and take a pic of it for you but that is a pretty fool proof description above

There are multiple threads on how to replace the switch most involve removing fans and/or top hoses. I only have experience of 16V cars. On a 994S my recollection is that I removed airbox and top rad hose to get to it from above. On S2 I got it out from above without removing anything other than skin from my knuckles. Couldn't get it back in form above though so had to jack up car and take of the engine tray and come in from below without removing anything else.

If I was doing it again I'd go straight in from below for removal and replacement. Have the new one ready to pop straight in so that you don't spill too much radiator fluid. Make sure the motor is not too hot because you may get a green shower!

When it is back in bleed air out of the system as per Clarkes garage instructions .. not difficult and do it before you take car off axle stands. Oh ... last thing ... don't forget to put the fan relay back in!!

Let me know if you need a pic. Good luck!

[beamishnz]

Just looked up info in ISV too ... I've not had to tackle that but looks like a good suspect for uneven tickover if you have eliminated vacuum leaks and checked the sensor resistance. The other thing that I'd check would be cylinder compressions. Broken valve springs are not uncommon and would definitely cause rough idling ... not so noticeable as the engine picks up revs. Good health check for a new (to you) car in any event.

Get your thermo switch changed out first ... at least that problem will have gone away

[cockerpunk]

start cheap and easy .... plugs, wires, cap

[Jfrahm]

good tips. It should be determined if it's rattling around due to bad engine mounts, leaking exhaust (sampling tube rusted off?) or if it's actually running badly at idle.

The alternator is probably fine, the dash gauges generally read low but it's easy to check with a voltmeter.

[Panic_1302]

Found it thanks to your instruction Beamishnz it's been mentioned to also check temperature sensor and wiring for short circuits and rips so I may do that too.

[beamishnz]

Cool .. I knew you would ... I've had 2 of these fail on different cars over the last year so I'd think there would be a good chance that the sensor will be the cause of the fan run on ... the rough running will be probably be less easy to track down but most of the things that you do on the hunt will be beneficial for the future good running of the car so not lost time or $$.

I had a 944S that I had that I checked everything on only to find a new set of plugs did the trick ... for the S2 go for Bosch OEM copper WR5 DC+ ... I've not had good results with platinum/iridium etc. Cockerpunk maybe right ... plugs, leads, cap and rotor are an easy swap out and worthwhile if running original Beru set up, but I'm not sure if I agree with him re 'cheap' - these parts are pricey for the 16V cars. Don't go for chinese leads. Stick with Beru/Bosch caps ... I found some Bosch leads with Beru caps that were cheaper than Beru/Beru and good quality. Have a good hunt on Ebay or Pelican do a reasonable value 'Tune up kit' too. Have a really good look at any service records that came witht he car. If something has been changed in the last few years then you obviously don't need to be changing it again.

All these little things tend to be ignored by 'previous owners' and you will be plagued with niggley problems until you go through and check/replace the items discussed above. the cars are 23+ years old and a lot of the sensors and rubber suspension components are passed their usable life - they may still be functioning but at any moment .... they won't

[Panic_1302]

Thanks sausagehacker, cockerpunk and Jfrahm. When I move into dealing with the idle issue after checking the rad thermoswitch problem I'll review this feed once more. This was awesome. Thanks again guys

[sausagehacker]

When I said coolant temp sensor, I should have clarified as there are 3!

- Fan switch in radiator you found
- Temp sensor for gauge
- EFI temp sensor (the one I should have explicitly mentioned).

The latter of the 3 is an input for the DME and can cause funky running if readings are off, the same way a bad O2 sensor can.