Porsche 944S won't idle at all.

SloMo228 · 04-09-2015, 02:51 PM

I just got done swapping an S2 intake manifold onto my S. Prior to the swap, I had high idle and hunting issues, so while I had the manifold off I replaced all the vacuum lines with silicone hoses, re-sealed the AOS and replaced the oil filler cap, re-sealed the S2 throttle body, and moved the AFM arm to slide on a new track.

I am using the S2 throttle body, the S AFM, and the ICV that was on the S2 manifold. I initially suspected the ICV since I can get the car to start and run if I feather the throttle manually, but even when the engine warms up to operating temperature, it just dies if I'm not keeping the pedal slightly pressed.

The ICV doesn't vibrate with the key in the ON position like I've read it's supposed to, but it does make a clicking noise when it's plugged in or unplugged. However, from what I've read, even if the ICV is malfunctioning, the car should idle normally once the engine is up to temp, right?

My O2 sensor is newer, replaced less than a year ago. I cleaned and re-sealed the fuel injectors, my FPR and damper are both only a couple of months old.

The AFM is missing the cap on the adjustment screw, if a PO had messed with that to get it to run with what I'm sure were multiple vacuum leaks, would that put things far enough off that it won't idle at all now that the leaks are fixed?

The 16 valve motors don't have the idle adjustment screw like the 8 valve motors do, so that's no help to me. The factory manual I'm looking at says that the idle is not adjustable on these cars. I can adjust the throttle stop but don't want to just be diving in and making a bunch of adjustments without knowing what the problem is.

Any suggestions? Anything I might have missed? Thanks in advance!

race46 · 04-10-2015, 03:16 PM

Had the same problem with my s2, Idled all over the place, sometimes ran at 3000. I assumed like you did it was a vacuum leak, or icv valve. Hunted for weeks - never found anything. Changed throttle position sensor - nothing. Changed the crank sensor - nothing. Finally changed the AFM - Bang the thing runs beautiful. Have you looked at the AFM under the plastic cap to make sure its clean? Or do you have access to a used one just to swap and try it out?

SloMo228 · 04-10-2015, 06:18 PM

Quote:

Originally Posted by race46

Had the same problem with my s2, Idled all over the place, sometimes ran at 3000. I assumed like you did it was a vacuum leak, or icv valve. Hunted for weeks - never found anything. Changed throttle position sensor - nothing. Changed the crank sensor - nothing. Finally changed the AFM - Bang the thing runs beautiful. Have you looked at the AFM under the plastic cap to make sure its clean? Or do you have access to a used one just to swap and try it out?

I don't have access to another one to swap but it's the original S AFM. I pulled off the black cap to slide the arm down its shaft slightly so the electrical contacts would slide on a new track - the resistive material was worn off a good bit of the original track.

This weekend I will get some time to fiddle with the car. I'm going to try messing with the AFM bypass screw to see what happens, I guess. Someone's clearly adjusted it in the past, so I'm hoping it's just a case of it being adjusted way off to compensate for vacuum leaks.

It seems that the S is pretty prone to these kinds of problems. I had thought the S2 intake swap would help - hopefully it will once I get the idle sorted. On the plus side, I can drive it except for the idle problem - it's definitely peppier and the throttle response is way better.

SloMo228 · 04-12-2015, 05:58 PM

Well, I got it idling, though it feels like I cheated. Messing with the AFM screw had absolutely no effect at all on the idle, even going from one extreme to the other.

I ended up adjusting the throttle stop to open the throttle plate enough to allow the engine to idle. I don't think that's the correct way to fix the problem, though I'm not sure what else I could do. The S and S2 motors don't technically have an idle speed adjustment, so there aren't many options for altering the idle.

djnolan · djnolan's Garage

Something has to be wrong with your setup. Check your large vacuum and air hose routing, including the venturi, brake booster, AOS and ICV lines and make sure they are connected and clamped. To me it sounds like there is a large vacuum leak somewhere in one of these areas.

SloMo228 · 04-13-2015, 03:04 PM

I pulled the manifold off again to double-check all of my vacuum connections. I deleted the venturi, so that's not a potential leak point. All of the vacuum hoses are new and tightly clamped. I have one small vacuum line that Ts off in two places to feed the fuel damper, regulator, and vent valve, one large line for the AOS, one large line for the brake booster, one medium line for the vapor vent, and the ICV/ISV valve lines, which are also new.

The only vacuum lines I didn't change are the ones which go to the heating system, since there was very little space to reach them. However, those are small lines and I wouldn't expect them to have this much of an effect on the engine even if they were completely broken. I could be wrong about that, though.

The only possible place I could think a leak might be is from the AOS "cap." I have read that there is a large o-ring in there that can break down and develop a leak. I did not replace that part of the AOS, just the O-ring seals where it attaches to the block and the oil filler cap itself.

There were three "extra" ports on the S2 throttle body, which I capped with rubber caps. Two of them were coolant ports, from what I've read. The third one was much smaller and was clearly a vacuum port. However, I had no other vacuum hoses to connect there, so I capped it.

djnolan · djnolan's Garage

Quote:

Originally Posted by SloMo228

The only possible place I could think a leak might be is from the AOS "cap." I have read that there is a large o-ring in there that can break down and develop a leak. I did not replace that part of the AOS, just the O-ring seals where it attaches to the block and the oil filler cap itself.

There were three "extra" ports on the S2 throttle body, which I capped with rubber caps. Two of them were coolant ports, from what I've read. The third one was much smaller and was clearly a vacuum port. However, I had no other vacuum hoses to connect there, so I capped it.

I would think if all of the ports on the intake and throttle body are connected or capped, it should idle. Are you sure about the ICV and brake booster lines?

SloMo228 · 04-14-2015, 06:57 AM

It's idling perfectly now. I swapped out the S2 ICV and put in the original S one after giving it a good clean and lube. It now idles spot on at 900rpm, and I was able to return the throttle stop to its original position. So it was either that or I unwittingly repaired a vacuum leak when I pulled the manifold to swap the ICV. Either way, I'm happy.

Now that it's idling properly, though, I've discovered I could use some new motor mounts!

SloMo228 · 04-16-2015, 07:30 PM

Just wanted to check back in - the S2 intake swap was definitely worth it. Aside from idling properly now, the car has noticeably more power at pretty much all RPM. I was on my way back from work this evening and driving around a bend that I often take at WOT without issue. This time, with the S2 intake, WOT broke the rear wheels free and I ended up drifting through the corner.

Good thing the summer tires are going on soon!