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Hesitation when accelerating.

Old 02-28-2011, 03:55 PM
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Ky944TurboNewbie
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Default Hesitation when accelerating.

I have a 1986 944 turbo that has been sitting over the winter. I am trying to drive it now and it has very bad hesitation in lower RPM's. I believe it is the MAF sensor that is acting up again. It has been adjusted/cleaned a couple of different times over the last 5 years by different mechanics. Do you think it is worth trying to adjust/clean again or should I replace it. If you think I should replace it, are there any good options out there that aren't too expensive? I would hate to buy a used one with the same issue, and the rebuild's aren't cheap.

Thanks for your thoughts in advance.

Michael
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Old 02-28-2011, 04:42 PM
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Is it a MAF or an AFM? AFM is stock flappy door thing MAF is aftermarket no moving parts.
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Old 02-28-2011, 04:50 PM
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Sorry.... I guess it is the AFM. The 2 contacts with the wiper that controls air flow?
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Old 02-28-2011, 05:10 PM
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Sounds about right it would have a door in it that moves. So is the car stock? Have you checked the fuel pressure? AFM might not be the problem , is this happening under boost what rpm?
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Old 02-28-2011, 05:25 PM
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Hmm I looked at some of your other post, have you changed the fuel filter? And you definitely need to check your fuel rail pressure. You can spec out the AFM with an ohm meter and gently move the flappy door to see if it's sticking.
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Old 02-28-2011, 10:25 PM
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Clean you TB. Also your TPS maybe acting up.
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Old 03-01-2011, 01:07 AM
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First check the TPS, that's the easiest to do. Then check the AFM. (both multimeter checks). If both check out, then take a look at fuel pressure.
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Old 03-01-2011, 12:46 PM
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Don't overlook the sparkplugs either... I just had a running issue at idle, and low rpms that was fixed with new spark plugs.

Could be a slight vacuum leak somewhere too.. Does it run ok at higher RPM?
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Old 03-01-2011, 01:14 PM
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Sounds like it definitely could be the MAF if its stumbling under acceleration
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Old 03-01-2011, 05:28 PM
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MAF seems to check out ok. I thought this was the most likely as I have had trouble with it in the past. No drops in voltage across the entire range of the wiper. There are visible grooves there, but if the sensor is a problem, it doesn't want to act up now. Temperature sensor seemed a little out of the range. The reading was for 4.5 k-ohms. Could this cause the hesitation on acceleration?

I will check the TPS next. The hesitation didn't present itself until after the engine warmed up.
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Old 03-01-2011, 08:07 PM
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The TPS test failed on the lead from the DME wire harness. Looks like I need to source a new TPS.
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Old 03-01-2011, 08:50 PM
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If anyone has a known good throttle position switch for the 944 turbo, send me a pm with what you want for it.

Michael
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Old 03-02-2011, 03:02 PM
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Originally Posted by Ky944TurboNewbie View Post
The TPS test failed on the lead from the DME wire harness. Looks like I need to source a new TPS.
Hopefully this is it and you're on your way to getting it fixed, but just in case, since you're going to replace the TPS anyway, I recommend you remove it now and retest it via direct contact to make sure you get the same results.
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Old 03-02-2011, 03:15 PM
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Originally Posted by Ky944TurboNewbie View Post
If anyone has a known good throttle position switch for the 944 turbo, send me a pm with what you want for it.

Michael
TPS, $45 shipped. Go to:
https://rennlist.com/forums/944-turb...-and-junk.html
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Old 04-27-2011, 06:08 PM
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Update - I have multiple issues that I am working on. I have a leaky power steering rack, leaky water pump, and my poor running issue. After checking the clarks garage procedure again, I decided I had just misread the TPS results and that it was actually good.

Because I am replacing the water pump and timing/balance belts, I started looking at some other "while I am in there" items. I wanted to make sure I had a good head gasket so I pulled my plugs. They were very black. Bad carbon deposits. I have replaced the plugs and it appears to be running much smoother. I think it has been running really rich. I just plugged a huge vacuum leak. I didn't suspect the plugs at first because they were changed 3 times in the last 5000 miles. I need to figure out why the plugs are getting fouled so quickly after I finish my next projects.

Next up is Timing/Balance belts and rollers, front seals, power steering rack/pump and updated pickup line. Keep your fingers crossed for me. This is the biggest surgery I have ever attempted myself.
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