944S 16V won't idle!

[Timmay!]

Yesterday, Car was idling fine after repair from broken timing belt- till it got warmed up?
Suddenly, idle went up to around 1800. If I blipped the throttle higher, it would come down to idle- then go smoothly back up to 1800 rpm.
Started kinda hard when cold this morning.

*clue 1* If I disconnect what the factory calls the idle speed positioner (throttle bypass valve under manifold), the car will idle at 1100 rpm steady. If I reconnect the idle speed positioner plug , the engine will stumble and die.

*clue 2 * If I disconnect the vacuum line at the fuel damper, the rpm increases. Indicates no vacuum leaks? I also sprayed starting fluid around hoses and manifold and got no reaction.

*clue 3 * If I blip the throttle, the engine responds immediately then comes back to idle, which means the TPS is good. I can hear it clicking when coming off of idle.


Small Vacuum leak?
Bad idle speed position valve? is it dirty?

[djnolan]

Maybe the icv is stuck? Rap on it with something...

[Timmay!]

ok, ICV. Idle control valve is a better name for that thing. This one is the third generation of these things and they keep changing the name!
It gets input from the power steering pump, the a/c compressor, etc.
I'll try tapping it with a sledge....

[Timmay!]

Ok, another clue.
I banged on the ICV and moved it a little.

* clue 4 * Now that the engine is at the first tick on the temp gauge, and after I banged the ICV, and disconnected the ICV, idle went up to 1800 again. When I plug in the ICV, it drops the rpm to 1100-1200. I blip the throttle and it drops rpm and dies.

[JERRY B]

I Vote for the ICV Do you have a extra one. I sold mine to Mark R. as a spare
They are different than the 8V ones

[Timmay!]

Jerry,
Do I have an extra one? uh, No! Parts for these 944S's seem to be rarer than rocking horse $h!t!!
I had a different customer bring his 87 944S into the shop this afternoon for comparison. Vacuum lines routing verified good. Although when I pulled his ICV plug on his warm engine, nothing changed!?

I pulled and tested and swapped out the DME head temp sensor. No problem there........
Now's when I start drinkin' heavily.......
Smoke tester to find a vacuum leak is next. I sure picked a bad week to quit smoking cigarettes!!!!!!!!

[djnolan]

Spray carb cleaner in it and let it soak. it might be stuck because it is dirty. also if it dies there may be a cracked hose or loose clamps. a pita to replace the hoses because there is little room under the intake to work on a 16v.

[968 GUY]

Do a search for the wiring from the power steering pump.
If I remember correctly, the S version has been known to have problems with that wiring.

[Timmay!]

Everytime I connect or disconnect it, it causes a change, so I believe the ICV is not stuck and it's working correctly. I can't get to the ICV to spray inside it without removing the intake manifold again.
Yes, the P/S steering is an input to the ICV but I disconnected both wires to the pump with no effect.

[porschetub]

Sound like your icv may be ok,keep looking for air leaks,inlet manifold was where I found mine.

[Timmay!]

Right. Thanks.
Times are tough and the shop can't afford a smoke machine right now.......so I'm gonna have one of my employees who smokes just start chain smokin' and exhaling into the AFM. We're gonna leave the engine off this time though because last time it kinda sucked his lips and cheeks into the AFM and he got kinda mad.....maybe we weren't doin' it right........
Hold my beer...watch this.

[porschetub]

Very funny???,not sure how to take that one,sorry to have added my .5 of a cents worth,but air leaks are very common.

[Timmay!]

Porschetub,
Just kidding. I was making light of a frustrating problem.
I believe you're correct about an air leak.

[Timmay!]

OK, guys.
Did the smoke test and found 4 leaks.
1. Lower AOS O-ring.
2. Base of dipstick
3. rear of upper C/B shaft housing
4. rear of lower C/B housing

Got those sealed up thinking that was causing the weird idle condition. We didn't replace the ICV because it's very expensive and we thought we had found the problem. Manifold went back on and the idle improved. Also tweaked the throttle stop closer (1/8th turn) to where the TPS actually clicks. That helped.

Now, when cold starting, the idle hunts up and down then settles around 1,000 with rough running.
Engine still doesn't like to come back down to idle without stalling.
The car otherwise runs ok, but it doesn't pull hard at higher rpm's like other 944S's I've driven. Could this be an ignition timing thing? We set the rotor per the factory manual procedure.

[Timmay!]

Well, pulled the mainfold again. ICV on order.

[Timmay!]

OK, new ICV installed. That improved the idle some, but didn't fix the problem of it hunting.
Earlier, I guessed that there were multiple things wrong at the same time on this high mileage 944S.
Since the AFM cover had silicon around it, I popped that off.
Found that the curved contact strip at the idle area was worn out. So I bent the arm to make a fresh sweep track. That seemed to help some. Now the engine doesn't die when I blip the throttle.
But it still idles high when cold, and jumps to 2200 rpm when warm. Before it went up to 1800 rpm.
We'll check/set the CO today, but I wanted to check one more time for any vacuum leaks so we smoke tested it again. Found a NEW leak in one of the old hoses! They don't like to be bent!
Also, since the other bigger vacuum leaks had been found and fixed, now smaller ones have surfaced. The throttle butterfly shaft was leaking some and since the AFM cover was removed, we started seeing smoke come up there. I'm not so worried about that last one because the AFM will be resealed.

[djnolan]

if you have the intake off, replace all of the vacuum, idle and crankcase vent hoses. At 25 years old just moving them will cause more cracks and leaks.

Also try using spring clamps instead of the screw type barrel clamps. First of all the barrel screw clamps need to be periodically re-tightened as the hoses shrink due to heat. 2nd, on an S motor they are very hard if not impossible to access to tighten once the intake is installed. The spring type will never need re-tightening. If you can't find spring clamps new, try a junkyard. Lots of cars have them on the cooling system hoses.

[Timmay!]

Ok, got it.
As previously guessed.......more than 1 thing wrong at the same time.
CO was WAY off and so was the spring setting in the AFM. Someone must have tweeked the spring to account for the airleaks in this tired old engine in order to keep the car running.
When we redid the head, put it back together and sealed up the airleaks the mixture was suddenly way off. The owner of the car said it was a daily driver so we kept thinking it was something we did wrong. Nope, we did it right. The car's settings were just way off.
All better now.

[Rasta Monsta]

Yay Timmay!

[Timmay!]

Rasta,
Thanks, but it doesn't feel like a big victory because of how long it took. As long as it serves as a lesson for those that come after us, I'm content. We know alot about 944's , but not everything about 16 valvers.

...at your service,
TC