924Board.org

[Cedric]

[Raize]

Does this only occur when transitioning to/from a completely closed throttle? Or is it also a problem transitioning to/from small partial throttle openings to large ones?

[Maleraj]

Did you ever find a solution to this? Because I'm having the exact same problem, and I've soon swapped all parts of the drive train with no success.

[SecaBlue]

[SecaBlue]

[SecaBlue]

An update to this thread.

Upon first cold start this year after winter storage, the car was really not happy. I made sure there was fuel pressure, and could not hear the fuel pump running. But initial start was terrible. Had to try several times to start it where it actually kept running, and then only wanted to idle at 500rpm without some encouragement with my right foot.

Once running, it was spluttering and missing. Drove approx 10km (had to move garages). Tried a warm start, and it struggled, spluttering etc. but after 10 seconds idled ok.

2nd drive two weeks ago I took it for approx 45mins. Higher speeds, lower country driving, finding redline several times. Under throttle it drives amazing... revs up from around 1400rpm well, (even in 5th) with no flat spots, and very energetic at mid to high rpm. Temp stayed perfect, and once home it idled approx 850rpm indicated.

3rd drive this week - approx 40km at low and high speeds. Upon cold start in garage this time (ambient temp approx 17deg), it kicked over first time and only after a second or so. But was a rough idle at about 650-700 rpm, like one cylinder was in operation every now and again. I was in a hurry time wise, so just started to drive it. Engine was very unhappy at low rpm until up to medium to normal operating temp. I had to stop for a train crossing during the latter part of the drive, and the idle sat 850rpm quite ok with a slight miss or cough every 10 or 15 seconds. Once home a few more klms, it was idling perfectly - no cough, no miss. Also started warm again instantly and idled again at 850rpm.

Then today I did another cold start (ambient temp 16deg)... car started instantly but only wanted to idle at 700-750rpm, with a bit of a cough and miss sort of sound. Giving it some throttle, it holds say 2000 or 3000 rpm cold or warm with no miss or cough. Throttle is very responsive, and when parked and blipping throttle up to approx 2000-3000 rpm, I get a little popping from the exhaust.

No black/white/blue smoke from exhaust at either cold or warm idle. Smells just like an 80's exhaust does I guess

Considering last year Porsche workshop changed the timing belt, re-checked timing, fixed vacuum leaks, and adjusted A/F, where should I start now?

Just drive it more?
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold).

[SecaBlue]

A quick update...

I checked resistance on the WAR - was approx 17-18. Tested voltage to both electrical plugs for WUR and AAV - both were reading approx 13.5/14v upon cold start.

Removed AAV, seemed ok. Cleaned it a bit and after 2x rounds in the freezer and then hitting it with a hairdryer, it seems to move more. I also cleaned the ground contact on the mount, and electrical plugs.

Hard to know about cold start, as it currently 24 deg here today. But one I thing different is now when it starts warm, the idle starts with a kick up to approx 1100rpm, quickly settling back down to approx 800. I then dialed up the idle to indicated just over the 800 mark. Seems to idle ok warm, but still with a very slight miss or cough every 5-10 seconds.

Will have to wait until a cold morning to test the cold start again.

What are people's thoughts.
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold).

[Beartooth]

That first start coming out of winter sounds like air getting in the system and/or fuel getting stale in the lines - probably gumming things up a bit too. Any air should work its way out pretty quickly, but gum and varnish would take time to dissolve. One other thought: if you haven't replaced the injectors and they're marginal, you're going to have a lot more issues at idle and low throttle. One thing I noticed on mine was I had a couple that would dribble when I applied fuel pressure and just cracked the air flow plate (which would simulate a start-up situation); if I pushed the plate open a ways and then backed down they tended to give a more acceptable spray pattern. I need to re-check those - they may have cleared up from putting fuel through them over a couple thousand miles, but they may still need to be replaced. I do notice mine feels like it's on three cylinders when I start it (mostly cold start), which may be injector-related, but I do know #4's rings are pretty much shot.

Anyway, it sounds like it's getting better, and I would try to put more miles on it and see what happens. About the only thing I'd consider throwing at it based on what you describe (and assuming they haven't been replaced) is a set of injectors. The Haynes manual gives 30 ohms as a spec for the AAV; I can't find one for the WUR, but it should be in a similar range. On trouble-shooting that, I wouldn't worry about it unless you're not seeing a change in control pressure (the pressure in the line from the top port on the fuel distributor to the warm-up regulator), or if cold control pressure seem right, but warm pressures won't come up high enough. I cleaned my AAV by spraying brake cleaner and compressed air through it, and it's doing exactly what it should from all I can see. I re-calibrated my WUR, but no issues with the electrical side. When it's working correctly, the bi-metal arm that pushes on the springs inside to reduce cold control pressure pulls back and is completely out of play when it's warmed up. The resistance you mention sounds fine; you'll want to hook your pressure gauge up to the control pressure circuit and see what it does when you jump the fuel pump relay (ideally pull the injectors with the lines still attached and stick them in jars to make sure you're not dumping fuel into the engine - there should only be a bit of a drip with the air flow plate at rest though). It should start around 1.5 bar and rise to 3.6 bar in five minutes or so. If the pressures are too high, flush out the lines and the WUR before you do anything else. If they're too low, but do rise with the fuel pump circuit energized, start looking into WUR adjustments - there are a few good threads here on that.
_________________
1980 931 diamond in the rough

[SecaBlue]

Thanks for that info

I don't have the tools to measure pressures, etc. I am currently just going by ear and trying to work through things.

Do you really think the injectors would be bad with only 10,000 km on them, and if the car runs really well at any rpm above 1500 to redline?

I do now have a side effect from removing, cleaning, and reinstalling the AAV. Now when the car starts cold (well, ambient temp is 20degC), it tries to start immediately but dies, then it cranks and cranks with no start. Eventually after approx 5-10 seconds of cranking, it turns over but really rough. Doesn't want to idle cold over 600rpm, and smells from the exhaust like it was flooded.

Since the previous A/F tune by Porsche last year was done before my review of the AAV, could it have been that the AAV was too open during the tune, and now it is closed more at cold start?

Should I attempt in trying to lean out the mixture a little? The cold start is much worse now than before my AAV remove/replace.

Hmmm...
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold).

[morghen]

This amount of time writing these posts could be spent enjoying driving the car..if it had an EFI kit fitted

Joking aside I'm sorry to find that you are still having this issue.
_________________
Supercharger and EFI kits
https://www.the924.com

[Beartooth]

The AAV draws metered air, so the only thing that should change would be the idle RPM. That said, it's possible you either created a vacuum leak, or that you had a vacuum leak that was fixed when you re-installed. Definitely double and triple-check for vacuum leaks. With or without a fuel pressure gauge, it doesn't hurt to tinker with the idle setting. Much like a carburetor, you'd want to warm it up to operating temperature and then turn the mixture screw lean (should be counter-clockwise) until it starts to stumble, then back rich a quarter turn or so. The book calls for adjusting based on CO readings, but that's not necessary - if anything, it'll run better if you tweak it by feel. If it still has trouble on cold starts, you can try just going a full turn lean and see if that improves anything. If it does, but the warm idle is worse, then it's probably something out of whack in the WUR. You could make adjustments to that "in the blind" if you understand how it works, but it's a shot in the dark; a standard washer added or removed from the mount for the arm would be a pretty big adjustment. It's not impossible to make positive adjustments to the system without a gauge if you understand it well enough, just very difficult... I really like K-jet - it's simple, pretty accurate for what it is, and works great once it's sorted (other than hot starts, in my experience). Of course, it can't match a well-tuned EFI setup, but it can get along just fine. Oh, and if you know the injectors have been replaced, then I wouldn't bother with them. Wouldn't hurt to check the spray patterns and that they all have similar flow though.
_________________
1980 931 diamond in the rough

[SecaBlue]

Thanks for the info again

My thoughts are as follows... mixture was tuned in by Porsche with the AAV not operating properly - If I run this scenario in my head (with basic mechanics mentality) that the AAV was both not opening fully when cold, and not closing fully when warm (leaving the normal small hole), then Porsche was trying to tune the Co2 and idle with incorrect airflow.

Now the AAV is opening more at cold and closing more at warm, the engine was initially being starved of air (running rich) at cold, and now is getting too much air at cold compared to the current mixture settings.

When I drove it warm after my AAV review, without fiddling with the idle at all, it wanted to idle warm just under 800. One thing I found odd was when I tried to lift the idle to say 850, it took almost 1.5 turns of the idle screw before it started to lift the idle considerably. I turned it back again to where the engine started to complain (approx 600rpm), and then slowly back. Was only a slight turn to get to just under 800, and then quite a lot of turning to get higher than that. I thought it would be linear, but this may give a clue to something happening with the WUR or mixture.

Remember, the AAV, WUR, CSV are all original on my car with only 10300km since new. So when I said the injectors only have 10,000km I meant they are still most likely the factory installed ones. I don't have any idea what the previous owner did to the engine, although I believe he did nothing when getting it back on the road again in 2016. I only know he changed the fuel pump, and reviewed the brakes, and had a new timing belt done then too.

So is my logic sound?... If the engine smells like it is flooding on cold start, but starts instantly and perfectly on warm start? Maybe the WUR is needing a clean too even with the low klms on it, as I was also told before buying it that the k-Jet doesn't like to sit for years without any fuel flow through it.

I can't imagine that I created or fixed a vacuum leak, as I have not touched those lines, and they were checked by Porsche last year. Surely too with a vacuum leak the car would not run as well as it does when warm. I'll check though with soapy water later today (no access to smoke).
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold).

[Beartooth]

Oh, if the injectors are original, even thought very low mileage, they may be a problem. I'm not sure if they mechanic who tuned it would have looked into that, but you'd think being Porsche, they'd at least suggest replacing anything that might matter. You can test them by pulling the injectors from the intake, but leaving them attached or re-attaching them to the lines, stick each in a little jar, and jump the fuel pressure relay. Then, you'll probably have to go one by one, pull up on the air flow plate and observe the spray pattern into the jar. Oh, and definitely do this outside, with a fire extinguisher handy, and I like to disconnect the battery, jump the relay, and then turn the pump on and off by connecting and disconnecting the battery. What I found with mine is that a couple of them wouldn't spray near what I think would be an idle position, then they'd produce a decent spray pattern. It runs ok though, so I've just gone with it, and they may have cleared up with more fuel run through them. Anyway, there's definitely a possibility of a leaky or dribbling injector or two, considering they're original. They take a long time to wear out from use, but bad gas and corrosion could easily ruin them. I'm still running the injectors, WUR, and AAV that came with my car. There's also a screen in the WUR I've had to flush out a couple times, and I've also re-calibrated it and replaced the o-ring. Finally, I have rebuilt the fuel distributor, but that probably wouldn't have been necessary if I hadn't sprayed brake cleaning in it trying to get the plunger free...
_________________
1980 931 diamond in the rough

[SecaBlue]

Ha... well, when you start talking about jumping relays, etc, it gets a bit beyond my confidence

Checked for vacuum leaks... none as I thought.

Yesterday I did start to re-tune the mixture. A few things to note:

The hole where the hex key goes into on mine has a red coloured inner sleeve with the hole just big enough for the hex. There was no plug blocking this 'hex' hole, and I have read that there should be? I looked back in photos when I bought it, and there was nothing plugging this red sleeve hole when I bought it too. I have read that it needs to be plugged.

I let the car warm up, and then turned off, turned back the idle screw all the way, then 2.5 turns out. Then started the car, inserted the hex, and started to turn it. If I carefully turned even 1-2 deg anticlockwise, the engine almost immediately wanted to die. So I tried the other way.... it took approx 45deg turn clockwise before the engine idle lifted to sit around 900rpm (at the 2.5 idle screw turn position). But then I took out the hex, and turned off the engine, started again warm perfectly but idle then sat around 1000rpm. So dialed back the mixture until the idle sat at 900 again. Took it for a drive, and the jerking I was initially writing about in this thread has been reduced significantly. But I could not test a cold start until today.

This morning I tried a cold start and the engine just cranked and cranked - no sign of starting after about 10-15 cranks. Stopped, and tried again - after approx 10 more cranks it kicked over very rough for approx 2-3 seconds before smoothing out but with the idle only 700rpm. Even with some right foot, the idle didn't want to lift until warm, and then sat on 800rpm. Tried adjusting the mixture again clockwise until idle lifted more... took approx another 25deg turn before any idle lift was noticeable. Left as is for now.

I had a friend check the exhaust at current mixture setting - absolutely no black smoke in exhaust, and the throttle is very spirited from idle rpm, with no bogging, popping, or missing anymore.

So maybe the WUR or CSV is still causing the cold start issue, as starting and running warm seems to be much better.
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold).

[SecaBlue]

A small update... checked CSV injector spray - works absolutely perfectly with nice, even, fine mist at cold crank. This also leads me to believe that the engine injectors are most likely also fine, as the CSV sitting more without use logically means it has the risk of corrosion more so if not used as much. But I might stand corrected if someone has a different experience.
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold).