944S sluggish/buggy

[xero]

Hi, I have a 16v 944S.
It's quite slow(much slower than my NA 8v 944 and even my girlfriend's honda lol)
It really gasses out in the upper rpms but is slow off the line as well. The shift light comes on very early, like 2500-3000rpm which seems weird, and when I am decelerating with the car in gear and my foot off the gas, and then re-apply my foot to the accelerator pedal nothing will happen for a few seconds and then it will gradually start responding and then drive as normal. Happens every time I slow down with the car in gear and my foot off the gas.

It also idles high (1400rpm) which I figure is a vacuum leak, but the car did all the same stuff before the high idle developed, so I'm guessing it's un-related. I have checked the cam timing and even the camshafts timing in relation to each other, and both seem correct. I had another S years ago that did the exact same things, and I was never able to fix it. Never seen an 8v 944 act like this though.

Anyone have any experience with this, or any suggestions?
Thanks!

[Rasta Monsta]

Have your girlfriend get out of the Honda and depress the throttle pedal while you watch in the engine bay, making sure the throttle opens completely when the pedal is floored.

[xero]

Ok, I can check that. I'd be REALLY surprised if that was the issue though. Is there a reason you know of that would make a mal-adjusted throttle cable cause the car to not respond after deceleration, or are you just kinda throwing something random out there? Thanks.

[xero]

That makes me think though, I wonder if a bad TPS would cause something like this? DME might take a minute to recognize that you are pressing the accelerator. Hmm guess I gotta test that.

[joeblow]

Check that the cam timing belt has not slipped!!!

Also check the vacuum line to the FPR, make sure it is not off or broken.

Listen to the top of the cam cover for any rattling, could have lost the chain tentioner which will be followed by a broken head if it catches the chain and rips out! This is cause the cam timing to be very far off.

Check that the ignition rotor has not lost the retaining screw and slipped off its position.

Your cat converter may have failed and clogged to the point it is restricting the exhaust. You can also collapse a pipe in the system too or bottom out doing the same.

Your AFM could be getting stuck too with too much gunk in it.

[v2rocket_aka944]

while there may be some issues, even a cherry-running 944S is a dog below 4000RPM.
they just dont feel that fast until you come on-cam at the high end.

[djnolan]

How many miles are on the car?

My 87 944s is low mileage and feels just fine. The power feels even from idle to high rpm.

[xero]

I've previously verified everything suggested except the vacuum line to FPR, I'll check that. Though I don't think that would cause it to cut out after taking my foot off the gas while in gear. I've looked around in these forums and found several posts all describing the same thing, and all on 944s models.
To clarify and re state, taking foot off accelerator while in gear and in motion for a few seconds will cause to motor to not respond when re-applying pressure to the accelerator.
It will make bogging sound comin through the intake, but it seems like the fuel injectors don't kick in for about 5 full seconds of gas pedal pressing. Then it seems to graally realize what it should do over another 5 seconds and will start responding and driving as normal more or less, though still just kinda sluggish.

So is there anything fundamentally different in the S models fuel injection system compared to 8v as far as anyone knows?

[djnolan]

Have you tried to find the source of the fast idle? If it is from a vacuum leak, low vacuum might also be affecting the fuel system. If it i because the throttle is not closing fully, the throttle position switch won't trip. Either of these could be the cause your drive-ability system.

[mytrplseven]

Lots of good ideas here. Quick check: see if the vacuum line to the FPR has suction on it when the engine is running (vacuum line leak); smell the end and see if it smells like gasoline. If so the FPR is likely bad. After the engine cools, and in a quiet place, turn the throttle cam on the throttle body by hand and see if you can hear the faint "click" just as it starts to move and that the spring fully re-seats the shaft to fully closed. Also check the switch contacts with an ohm meter to verify the switch is good.

Also consider the O2 sensor. It can cause weird accel issues. These are my candidates.

[speedysprocket]

Yes, FPR can leak fuel into the vacuum line and thus into the manifold and flood the engine out. The engine creates the most vacuum in gear, at speed, throttle closed. So that's when it would suck the most fuel in. Then you step on the gas pedal and it takes 5 seconds to burn all that excess fuel off.
I'd also suggest popping the cap off the air flow meter and checking the condition and operation of it.
And finally, the TPS on these cars is nothing more than a switch to tell the DME throttle position is at idle, and a switch for wide open throttle. Not a lot to fail there, and if it does, I don't think it has a big affect on anything.
I did have a cat come apart once and blocked the exhaust- car ran poorly then...

[xero]

Wow, that's a very interesting theory on the FPR Speedysprocket!
I'll def look into that. If that were the case, I could test it by removing the vacuum line from the FPR, I'll try that first!

Also check TPS, and O2, and check for general vacuum leaks while I'm at it.
Thanks guys, I'll let you know how it goes.

[speedysprocket]

Just take the vacuum line off both the FPR and the fuel pressure dampener- one is at the front of the rail, the other at the rear. Start the car and see if fuel dribbles out...

[xero]

Well it's not the fpr or dampener, the lines were already disconnected from both haha. Need to take some time and chase down all my vacuum leaks on this thing and get the idle down. Should make diagnosing other problems a little easier!
But I was thinking, could it be sucking fuel out of a leaky injector in the same way?

[xero]

Tps clicks when closed also. I'll test the electrical function of it soon also.

[DannoXYZ]

Vacuum line disconnected from both FPR & dampener would cause severe driveability problems.
Hook those back up.

Also hook up vacuum gauge and measure vacuum with warmed-up car at:

1. intake-manifold
2. FPR
3. fuel-dampener

[jhowell371]

It's grasping at straws but I just read a period road test on my S2 and they mentioned that Porsche had fixed on the S2 a problem with the S. It seems that an overly sensitive knock sensor would retard the timing resulting in, (dramatic pause) poor performance. Mentioned a few pages into this article.
http://gallery.rennlist.com/gallery/album394

[xero]

Interesting, it does have that retarded timing feel to it. So the fix for thT would be to replace the knock sensor with an S2 unit...or maybe just unplug it as a test?

[jhowell371]

Got out my 89 S2 Porsche Service Information manual and basically it says the change was in how fast the spark re-advanced (in.75 degrees increments) after being retarded 3 degrees by the knock sensor. The S model stretched it out over a much wider RPM range thus taking longer to return to normal. This might be one area where an aftermarket chip might be an improvement if it followed the S2 advance curve. I don't know if it will run with the sensor unhooked but you can try. The S2 requires high test fuel so I assume the S does too. Maybe a different brand of gas might help. I don't use off brand gasoline in the S2.

[gtroth]

I'd find the unmetered air causing your high idle (vacuum leak or stuck open ISV).
And I always suspect the AFM since my severe hesitation problems were ultimatley solved by replacing the AFM.