[SILVY968]

My problem is that when I stomp the pedal from an idle, the engine does not rev up immediatly. The only way to get the revs up is to gradually press on the accelerator. The engine feels like it is about to stop...too much air, not enough fuel.

This does not happen at higher rpms, while driving.

I wonder if anyone can suggest what I might check.

air sensor? fuel filter, pump?

Any ideas what to check and how?

Thanks

Brian

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[Greimann]

Try a couple of tanks of fuel injector cleaner. If that doesn't do it, try this:



(my cut and paste from another hesitation thread.)



Typically, in any engine, hesitation can be cured by advancing the timing. Considering that the 968 has non-adjustable computer controlled timing, the only other way to bump the timing is to feed it more fuel or a higher octane too keep the knock sensors happy. When they are happy, they don't tell the computer to dial the timing back.



Try 5 gallons of 100 octane race gas. If you can't find that, then go to a paint store and get a gallon of toluene (sometimes labeled toluol) and dose the tank. This blend will bump the octane 3 or 4 numbers and tell you whether your hesitation is octane, and therefore ignition timing related.



Otherwise, try changing the O2 sensor. They need replacement at about 70K to 80k miles and directly affect the fuel mixture.

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[SILVY968]

[quote name='Greimann' date='Jun 18 2005, 06:54 PM']Try a couple of tanks of fuel injector cleaner. If that doesn't do it, try this:



(my cut and paste from another hesitation thread.)



Typically, in any engine, hesitation can be cured by advancing the timing. Considering that the 968 has non-adjustable computer controlled timing, the only other way to bump the timing is to feed it more fuel or a higher octane too keep the knock sensors happy. When they are happy, they don't tell the computer to dial the timing back.



Try 5 gallons of 100 octane race gas. If you can't find that, then go to a paint store and get a gallon of toluene (sometimes labeled toluol) and dose the tank. This blend will bump the octane 3 or 4 numbers and tell you whether your hesitation is octane, and therefore ignition timing related.



Otherwise, try changing the O2 sensor. They need replacement at about 70K to 80k miles and directly affect the fuel mixture.

[right][post="6054"]<{POST_SNAPBACK}>[/post][/right][/quote]

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[SILVY968]

Read your earlier thread.

I'll try the suggestion.

Thanks

Brian

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[NeedPorscheSpeed]

Another possible culprit is your TPS (Throttle Position Sensor). Good luck. <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />

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[SILVY968]

How do I test the throttle position sensor?

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[NeedPorscheSpeed]

[quote name='SILVY968' date='Jun 19 2005, 11:56 AM']How do I test the throttle position sensor?

[right][post="6079"]<{POST_SNAPBACK}>[/post][/right][/quote]



Brian, this link should give you some excellent insight. Hope this helps.



BTW, I just had to replace the TPS on my 951, and it worked like magic. <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />



http://www.clarks-garage.com/shop-manual/fuel-06.htm

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[SILVY968]

I'll print The CLARK'S doc and test the TPS.



I ordered the O2 sensor, since it is original and my 968 has 125k miles on her.

By the location in the parts manual it looks like I'll have to drop the exhaust to change it.



Thanks

Brian

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[Greimann]

[quote name='SILVY968' date='Jun 19 2005, 07:46 PM']I ordered the O2 sensor, since it is original and my 968 has 125k miles on her.

By the location in the parts manual it looks like I'll have to drop the exhaust to change it.

[right][post="6094"]<{POST_SNAPBACK}>[/post][/right][/quote]

No need to drop the exhaust. It is within easy reach.

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[mike]

Brian...please let us know if the O2 sensor fixes your problem. I am very interested because my 968 seems to exhibit the same symptoms. I also have a '91 944S2 that feels (seat-of-the-pants) like it has better throttle response and acceleration from low rpm. My 968 idles fine and seems to do better when it hits about 4000 rpm so I just assumed that this was a nuance of the variocam. Since it is just my subjective seat and pants, I haven't done anything about it so far. I have been hoping to drive another 968 and / or have another 968 driver drive my car to see if there is a difference. BTW - My car has 46K miles.

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[SILVY968]

If I do not have to drop the exhaust it will be muck easier. Thanks for the heads up.



Mike, I'll let you know.

BTW I changed the original fuel filter this weekend and it made a noticable difference in the cold start as well as the hesitation. It is not ALL gone so I will continue with the O2 sensor., then the TPS test.



Just for fun, I unbolted the stainless steel exhaust tip and polished it with an abrasive brush on my drill ( got it from ACE HARDWARE - blue in color ). It took about 15 minutes and it looks great.



I also put on a silver "PORSCHE" decal at the top of the front windshield. It looks like the glass is etched, and looks great with the polar silver paint.



Can't wait for the next project- either bring to optimum stock performance or gently modify.



I am very glad that I found this group. You guys are helpful, knowledgable and best of all pure 968ers.



Brian

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[SILVY968]

Well, the o2 sensor was replaced and no change in the stumble.

The next step in the TPS. Is this a DIY?Anyone has tips and tricks?

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[SILVY968]

Getting readings that the HALL sensor on the cam is bad.

This may be the problem.

I'll order from Sunset and will post the result.

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[Cloud9...68]

Brian,



Sounds like you may be on the right track with the Hall sensor. I assume the flash codes test is what indicated it is bad. Someone on 968.net had a similar experience, and a new Hall sensor took care of his problem. In case that doesn't fix it, here's the list of things I went through in the many-month-long troubleshooting of a hesitation problem I had with my '92:



Car hesitates/stumbles badly when flooring it, particularly after about 20 minutes of driving. Seems to be worse in hotter weather.



- Checked engine flash codes (came up perfect)

- Tested throttle position sensor, and installed a spare someone loaned me.

- Replaced DME relay

- Cleaned throttle body with chemical flush

- Checked spark plugs (all perfect)

- Checked distributor cap and rotor (replaced 12/03. They are in good shape, but I cleaned up contacts anyway)

- Plug wires are just over a year old (but see below)

- Ran two tankfuls of dessicant to remove any water that may have been in gas

- Had injectors cleaned and blueprinted by Marren. Amazingly, this didn't help at all, though the car runs better than before when in its "sweet spot."

- Replaced fuel filter.

- Replaced coil with a loaner

- Added 5% toluene to tank to raise octane as a test of knock sensors.

- Replaced high performance Racer-X chip with stock chip; if anything, it made the hesitation a tiny bit worse

- Re-checked flash codes with stock chip; still indicated perfect

- Tested fuel flow volume; came out to ~900 ml in 30 sec, well within spec

- Sprayed carburetor cleaner around intake manifold; no leak detected.

- Vacuum gauge reads 14.5-16” Hg, with an oscillation about a range of about 0.5”, with a period of just over 1 sec.

- Disconnected variocam solenoid – no change

- Cleaned MAF connector



And finally, the thing that fixed it:



- Watched engine run in the dark, and saw arcing and flashing along the plug wires, and around the coil. Ordered new plug wires to replaced the Nology's installed by the previous owner. Like magic, hesitation is gone!



I hope the new Hall sensor fixes your problem. If not, I hope some of the things on my list will be helpful. Good luck!

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[6spcab]

[quote name='Cloud9...68' date='Sep 24 2005, 04:52 PM']Brian,



Sounds like you may be on the right track with the Hall sensor.  I assume the flash codes test is what indicated it is bad.  Someone on 968.net had a similar experience, and a new Hall sensor took care of his problem.  In case that doesn't fix it, here's the list of things I went through in the many-month-long troubleshooting of a hesitation problem I had with my '92:



Car hesitates/stumbles badly when flooring it, particularly after about 20 minutes of driving.  Seems to be worse in hotter weather.



- Checked engine flash codes (came up perfect)

- Tested throttle position sensor, and installed a spare someone loaned me.

- Replaced DME relay

- Cleaned throttle body with chemical flush

- Checked spark plugs (all perfect)

- Checked distributor cap and rotor (replaced 12/03.  They are in good shape, but I cleaned up contacts anyway)

- Plug wires are just over a year old (but see below)

- Ran two tankfuls of dessicant to remove any water that may have been in gas

- Had injectors cleaned and blueprinted by Marren. Amazingly, this didn't help at all, though the car runs better than before when in its "sweet spot."

- Replaced fuel filter.

- Replaced coil with a loaner

- Added 5% toluene to tank to raise octane as a test of knock sensors.

- Replaced high performance Racer-X chip with stock chip;  if anything, it made the hesitation a tiny bit worse

- Re-checked flash codes with stock chip; still indicated perfect

- Tested fuel flow volume; came out to ~900 ml in 30 sec, well within spec

- Sprayed carburetor cleaner around intake manifold; no leak detected.

- Vacuum gauge reads 14.5-16” Hg, with an oscillation about a range of about 0.5”, with a period of just over 1 sec.

- Disconnected variocam solenoid – no change

- Cleaned MAF connector



And finally, the thing that fixed it:



- Watched engine run in the dark, and saw arcing and flashing along the plug wires, and around the coil.  Ordered new plug wires to replaced the Nology's installed by the previous owner.  Like magic, hesitation is gone!



I hope the new Hall sensor fixes your problem.  If not, I hope some of the things on my list will be helpful.  Good luck!

[right][post="10232"]<{POST_SNAPBACK}>[/post][/right][/quote]



I ran into the same thing when I purchased my 968 as well. After a complete tune-up and fuel injector cleaning it is 90% gone. I am going to check the Hall Sensor on mine as well. Please let us know what you discover on yours. Best of luck.

Lee

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[6spcab]

Here is a pic of my Hall Sensor. I barely touched the ends when one of the tabs broke off. Probably was on it's way out.

Out of curiosity I reinstalled it as I had to move the car over in the garage. I went for a quick drive and the car actually ran BETTER. Hmmm. Not perfect but certainly better. I could hypothesize on why but that would be too much typing. I did get a code 1134 2 times early on but not in a while.

<img src="/forum/images/smilies/968/tongue.gif" class="smilie" alt="" />

Here is a pic. Notice the crack on the connector? I also noticed the manufacturer of the sensor-Siemens-German engineering at it's worst.

Now to find one with a decent price.

Lee

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[SILVY968]

Got the hall sensor replaced today and the stumble is gone.

The O2 helped, but the hall sensor made it go away. The butt-o-meter says that there is more power now. retarded timing is not good for performance. The cold start is better as is the idle hunting.

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