1988 944S Idle issues - mechanic touched the idle adjustment...

[Sefeing]

(x-post from Rennlist because I'm desperate!)

Hi all - having a major problem with my 944S after getting it back from the mechanic. Of course it's the weekend, so I'm troubleshooting myself now.

Brought the car in to a majorly reputable shop here in the NY area to have a few things looked at that I couldn't figure myself. Car idled fine when I brought it in, with the occasional stumble/surge that always seemed to work itself out.
At 115k miles, I had a feeling the ICV should be cleaned / replaced at some point but never wanted to touch the intake manifold myself.

Shop removed, cleaned and replaced the ICV, stating it was totally frozen when they took it off the car. They freed it up, put everything back together and "adjusted the idle" so the car ran at 1100RPM at idle.
On my drive home I noticed a few things - the car was a little odd to drive, it never really seemed to actually be "throttle off", and had a few stumbles where it'd idle at 500 - VERY low.

Once home, I checked the throttle to see whether the TPS was being contacted at idle. It wasn't.
I can hear this audibly, meaning they adjusted the screw that forces the throttle open/closed. Not something you're supposed to do on the 16V cars, and would explain why the car was driving odd.

I tried adjusting the screw so that the TPS was contacted when idle, but when seemingly correctly adjusted (just BARELY making the switch, but hearing the click when the throttle is closed, and open just off idle throttle), the car won't idle right. It drops down to 500, and dies. if I give it throttle, it'll stay alive but the second I let off, it dies.

I'd LOVE to get the car on the road this weekend for Father's Day. It will be going back to the shop Monday, but it's a huge disappointment.

My guesses are either that there's a big vac leak somewhere after pulling the manifold, or the ICV has finally bit the dust.

This was a notable shop that other members use, I guess they're just not as knowledgeable about the 16V cars.

​​​​​​​Any insight is appreciated.

[944 Ecology]

Before touching anything, I would do a smoke test to look for vacuum leaks. You may be able to get by with pressurizing the intake (no more than 5 psi) and spraying all the hose connections with soapy water, but not nearly as diagnostically effective as a smoke test.

Good luck and happy fathers day.

[Sefeing]

Originally Posted by 944 Ecology

Before touching anything, I would do a smoke test to look for vacuum leaks. You may be able to get by with pressurizing the intake (no more than 5 psi) and spraying all the hose connections with soapy water, but not nearly as diagnostically effective as a smoke test.

Good luck and happy fathers day.

Will give that a shot. Regardless, they have adjusted the throttle so that the TPS is not being contacted when the car is at idle- which is incorrect. The throttle should click a switch. If I adjust that to the correct position, the car sputters and dies.

[Sefeing]

Update: with the ICV unplugged, and the TPS switch made, the car runs - albeit idles high at 1100-1200RPM.

[944 Ecology]

Originally Posted by Sefeing

Update: with the ICV unplugged, and the TPS switch made, the car runs - albeit idles high at 1100-1200RPM.

Sounds like a vacuum leak between the afm and the intake manifold.

[Sefeing]

Originally Posted by 944 Ecology

Sounds like a vacuum leak between the afm and the intake manifold.

Smoke tester arrived today - could be a combination of a vac leak and a bad ICV. We'll see... It's going back tomorrow regardless to the shop.

The second the ICV is plugged in, the car bogs and dies

[kdjones2000]

I would electrically test that the idle switch "closure" is registering at the DME. Sound alone doesn't guarantee it's working correctly.

Pop off the DME connector and use a VOM and measure resistance between 24 AND #52.

[Sefeing]

Originally Posted by kdjones2000

I would electrically test that the idle switch "closure" is registering at the DME. Sound alone doesn't guarantee it's working correctly.

Pop off the DME connector and use a VOM and measure resistance between 24 AND #52.

Did this already! The switch checked out - registered under 10OHM when "idle" and open when throttle is depressed

[kdjones2000]

Sounds like you are doing things the right way, then. Good luck!

[Monkey Wrench]

I think porsche uses a similar one, i was just playing with a couple of examples. I noted that they both had an arrow that pointed the same direction but on one the stamp was on the opposite side, it did still point he same way.

I assume the arrow points to the fume direction in other words away from the sump and towards the intake manifold.

it made me wonder if the shop could have put it in backwards , and I also wondered also what would actually happen if one is installed backwards. I' d check that arrow to see which way it was put in. if its just one in one out , easy mistake to make.

I think some of them have three ports. most I've seen have 2 ports. ( 2 hoses)

[Sefeing]

An update here:

mechanic ruled out every other option and then compared the ISV to another one off a 964 he had apart (same part) and discovered that while mine moves, it's not fully opening / closing meaning the valve is kaput.

[Monkey Wrench]

id have a careful look at the hoses between the crank case and the IAC, those hoses live down in the the dark and hard to see and there is a lot of contamination and heat cycles. heat vibration and oil affect rubber life. from what Ive seen in old volvo's that can mean the 35 year old formed hose is as hard as a rock. likely with a hole in it. how expensive or hard to get are they?

[djnolan]

Originally Posted by Sefeing

An update here:

mechanic ruled out every other option and then compared the ISV to another one off a 964 he had apart (same part) and discovered that while mine moves, it's not fully opening / closing meaning the valve is kaput.

it may be sticking because it is dirty, spray in some carburetor cleaner and let it soak a while to see if it frees up.

[Monkey Wrench]

I noticed in some info that was comparing parts from other cars, that the same idle air valve was used by 1988 Volvo740 same one is used in comparable 240's

I just ordered a cheapo made in china one for my 1988 volvo 740 from the rock place.. wanted to see if it improved the idle by any amount. it has one inlet and one outlet, some used by Volvo have 3 hose connectors. the volvo one is aluminum or pot metal, the Chinese one was a lot heavier. I just received it yesterday

when I get further into my early 85 Porsche I'll have a closer look and compare side by side, might turn out to be the the same part, but I cant' verify with any certainty. Its not hard to swap in a Volvo. I noticed mine was vibrating, swapped it for another, but all I had was old used ones.

. I was ordering other stuff so I just wanted to see if it would make any noticeable difference at all. that car runs well but the idle sort of shakes the engine a little , i'll do the timing belt and others, summer maintenance. want ot see if the balance shaft in that car is in the right spot, if not I figured that might cause the shaking. so figured since I'm going in, new belts and tensioner, then it'll be good for another 100 K

cheap parts, I laughed at the size of box they used to ship two fan belts though, it was a huge box full of bags of air, and two little V belts at the bottom. the timing belt and tensioner were rolled up tight in a really small box but that was at their dayco factory. 5 boxes about 10 little made in china parts, it felt like christmas day ;-)

[wwdwgs]

MW,
Balance shaft misalignment (usually 180 degrees) will "show" itself at 3000 rpms and above.
Some Chinese products are fair in quality... Some...like 5% or so.
There are many Chinese cars in on-US market. They look fantastic from outside and fantastic inside. But, when you start to fix them, you'll see their "ugly" side. They don't last even "warranty" period.
Just for fun: name 10 things invented and built by "Europeans" and 10 - by Chinese.

[kdjones2000]

Yours is an ICV, not an ISV. Behaviour may be different.

[Monkey Wrench]

people who buy American cars thinking ll the parts are made in the US are being led, Yes I agree though, all made in china parts, buyer beware. some is fine, some is real junk.. country of origin isn't a reliable way to check if a part is good, Those days are past.
engineered obsolescence is built into almost every consumer product. Yes sure I'd take a Bosche part over one stamped made in china, but where the components of the Bosche part are created, that I could only guess.. so you trust bosche because you are buyin gthe name, how about Dewalt? good US tool company with a solid reputation right? sure yes, and made offshore for sure now, because it's not 1950 anymore.

I bet the source of , lets say an armature for a motor isn't well advertised, even though it says assembled in the US or mexico, its parts can very well be different.

I will say though, from what Ive seen I would normally trust an OEM bosche part over a made in china one and probably pay more for it.
If I order lets say wiper blades, there is such a range in price, maybe price means something so you look at the list of maybe 20 wiper blade manufacturers that fit your car,, well I might pick the middle, I know Ill chuck them in a year or two. I bet you'd be hard pressed to find a US windshield wiper factory.

We used to just change the rubber blade, now almost every one is a complete unit.

[Monkey Wrench]

Originally Posted by kdjones2000

Yours is an ICV, not an ISV. Behaviour may be different.

"idle air control valve" I think but I have a habit of messing up such terminology. and acronyms do always seem to get me, and Ill admit ISV draws a blank just now too.

i could be off on this but I "think" it stays open normally and when the throttle plate closes it enriches the mix by closing.. that would mean most of the time the ccar is driving and sucking up its own crankcase fumes and reburning them. at idle it may have a path but maybe a smaller hose?

next time I have one out Ill be more perceptive, maybe just connect it to the wiring plug off the hose so the engine can run and blow through it.

I " think" the arrow points in the direction of flow, to the manifold, not back to the sump.

I dont have a deep trust in the Chinese made one but maybe I can see some difference, just experimenting. Im not really sure if the thing is linear or if it is on and off, are there mid positions? I heard someone here refer to it as a "motor" I always figured it was basically an electric solenoid.

I happened to be troubleshooting something, got close to the thing with the key on , it was vibrating, I thought that's weird. if it was AC power I could understand that the electromagnet might have a 60 cycle hum and hence a resonance, but its DC what would cause resonance? I have to admit I dont really know everything , yet ;-)

[Monkey Wrench]

Originally Posted by wwdwgs

MW,
Balance shaft misalignment (usually 180 degrees) will "show" itself at 3000 rpms and above.
Some Chinese products are fair in quality... Some...like 5% or so.
There are many Chinese cars in on-US market. They look fantastic from outside and fantastic inside. But, when you start to fix them, you'll see their "ugly" side. They don't last even "warranty" period.
Just for fun: name 10 things invented and built by "Europeans" and 10 - by Chinese.

yes I agree, won't hurt to change the belt but doubt it slipped on its own probably the shaky idle is likely to be either an air/ vacuum issue , maybe timing is off. hard to nail it down. runs fine once off idle. i think I need to build me a smoke tester, I thought maybe I'd go buy a vape pen, I have a little air pump.. I already smoke , the last thing I need is a vape pen addiction too lol ..

[wwdwgs]

MW,
did you adjust the idle rpms? do you know how to do it right, involving a diagnostic port (over driver front wheel well)?
I set mine to 1000 rpms.
Here are the pictures (left hand index finger points at Diag. port location):


Here's a picture of jumped port:



Here's a link to a video:

https://www.youtube.com/watch?v=Yerr4jKlI1g