3.6 Starting Hesitation

Anyone have any idea what's causing this? It's intermittent, and happens more when it's a cold start. Porsche 996 Start Hesitation - YouTube

Huh? You get in the car and it fires right up. I'm not understanding the "hesitation" aspect. Don't know what the strange beeps are. Am I missing something here?

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Watch from 0:09 to 0:19, where it loses revs and then rebounds. That's my concern. The beeping is my V1.

Since yours is a 2002, have you done a e-gas re-calibration? Turn on car but do not start. Wait one minute. Do not put your foot on the gas pedal. Turn car off. Then start it and see what happens. BTW, is your SAI pump running on a cold start?

I saw two obvious issues: - The dash lights are flickering...possible electrical issue - The engine oil is overfilled Re the idle hunting, I like Joe's suggestion. Another possibility is a small intake air leak. Maybe you can scan the car for codes.

Voltage regulator could be kaput Could be a parasitic power drain somewhere Battery could be shot, but since you have adequate cranking amps, probably not. RPM dipping could be a vacuum leak, could be a MAF issue...

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I'll give this a try. And I'm not sure about the SAI... I'll check. Good point. The battery was replaced when I bought it from the dealer (May 2013). Oil wise - it's got about 500mL added from "two bars full" on the gauge. Not sure exactly how many bars I should be shooting for. I've got a goofy thing with the vacuum system on my muffler valves...I'll look into this vacuum thing a bit more. Any advise on the vacuum system?

I would say your car is shot and you should give it to me for free. I see nothing wrong.

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Dash light flicker is barely noticeable to the naked eye. I had to look twice without the camera on it. Tried this (egas reset, 60 seconds ON, OFF for 5, ON 15, OFF, START) and it hesitated just as the video showed. Either I screwed up the sequence, or that's not it. There's a high pitched noise that comes on from the engine bay when I ON...can't exactly place if it's the SAI or not, I don't feel it vibrating or anything, but that's gotta be it? New: after starting with hesitation (it doesn't always hesitate) I hear a very high pitched noise, haven't yet nailed down the source, but it only lasts 20 seconds or so, very audible from the cabin. I rolled down the window but it was gone before I could discern if it was an engine / SAI noise or not. Is a SAI delete (or pull fuse??) worth trying?

Next time you can leave the engine lid open when doing a cold start. Just go out to the engine bay and listen. The noise from the SAI pump will be very obvious if you're only a few feet from it.

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It's not just a high pitched whine? Video of the noise: Porsche 996 SAI Running? - YouTube It's just high pitched, and a *click* after 12 seconds that sounds like it's coming from the throttle body (can't get my head far enough into the engine to nail it down).

Normal. That's the from the throttle body and it's nothing to be concerned about.

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Ok so that's all good then with the SAI? So we're looking at something else for the hesitation? There was something somewhere that suggested perhaps a faulty engine coolant temperature (996-606-410-00-M100) could be the cause. Or back onto MAF? Or Vacuum... ugh.

More suggestions: It will involve a little bit of work - remove the throttle body, clean it, remove the idle control valve from the TB and clean it, remove the MAF sensor and clean it. I also see that you have an aftermarket air filter system and those have been found to have some issues, particularly when it comes to airflow past the MAF sensor. Any chance you have the stock air filter box and can re-install it to see if there is any difference? Also, sort of like since you are in there, check as many of the vacuum lines as you can get to. Look for disconnections, cracking and routing. The SAI pump runs after the engine is started and is totally obvious running...sounds like a vacuum cleaner, left side of engine compartment. You could pull the fuse or simply disconnect the wiring harness at the pump. In doing so, better have an OBDII code reader to clear the codes that will pop up and turn on the CEL.

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Good call on the aftermarket intake, Joe. All good suggestions.

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Here it is again on a buddy's car - X51 40th AE, all factory. It's not the intake, tho it may still be intake leak related? https://www.youtube.com/watch?v=Go6K...ature=youtu.be He's replaced MAF - no improvement. He's replaced the crank sensor - no improvement. Dealer thought his was the flywheel - replaced - no improvement. He has also replaced the AOS. Plot thickens: It only does this on a cold start when it has been driven recently (first start of the day). The starts coming out of winter storage (not running for months) were fine.

From the video...it is obvious! No gas! Or maybe the gas is old....I do have to say that sounds crappy. Know anyone that can put a Durametric on there? Short of doing all that I have put out there so far, I'm going for an some type of intake leak or vacuum leak. Have you also checked for a cracked oil filler tube? BTW, what maintenance has been done, i.e., plugs, coils, etc.

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Fresh gas, less than a week old. (in my video anyway, not sure why Nedster keeps his tank so empty.....) I use strickly Shell Premium (91 octane), with some PetroCanada Ultra94 for "spirited" drives where I'll be emptying the tank in a day and can refill with Shell. I just did coils & plugs a month ago (it did this before and after coil/plug change). Maintenance is quite up to date. Oil was changed prior to winter storage. Clutch / flywheel done 15k miles ago, along with IMSB and RMS. Waterpump, LN thermostat and coolant flush done last summer. Again, hesitation occurred prior to, and after, all this. I'll check for intake / vacuum leaks and put a durametric on it on a cold start over the weekend, see if I can catch some logs of it in the act. Then maybe a TB cleaning... A third sample from a friend: same issue, replaced injectors - no improvement. Local Indy suggested DME or VC+ actuators.

So are we trying to diagnose multiple cars on the same thread? It may get very confusing. For OP's car, if you suspect the SAI pump drawing too much current, you can just disconnect it and retry the cold start. Second Joe's suggestions, especially on intake leak. When you use Durametric for a cold start, it will help if you log all four O2 sensor voltage, MAF, misfire counters, RKAT and FRA.

I can assure you on my car, it wasn't because the gas is low The only thing i can add to the mystery is that if the car sits for a long time (over a month) it won't hesitate like that it will start just fine. I did all of the throttle cleaning, replaced MAF, new gas, no change. Not sure those three things ever fixed anything I am about to change the coolant temperature sensor as well with engine bay temp. sensor to see if that might be it as at least the coolant temp. value is important at startup. An indy suggested it could be go as far up as the DME, or VarioCam actuators.

After watching this video ( https://rennlist.com/forums/996-foru...any-ideas.html ) I can say my SAI pump has NEVER ran. Not once have I heard that vacuum noise. I don't recall seeing any codes on the dura for it... the car is getting a new AOS on Tuesday so I will pull codes and track starting after that.

That's very unlikely because the DME watches the SAI system like a hawk. Normally it sounds like a small portable vacuum cleaner but when its bearings start to dry up, it will sound like a benchsaw.

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It makes no noise whatsoever.

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Then it''s a mystery to me. Your car should have the same OBDII smog requirements...unless someone coded it out in a tune.

It appears you have Durametric. You can trigger the SAI pump and see what happens. Agree with Ahsai...the DME monitors the SAI and control valves like a hawk. Anything not right and it triggers a CEL and code. Unless, like he suggests, you have a different "tune" in your DME. And, you are not getting any OBDII codes...right?

Good luck. My 03' has a similar behavior, where on cold start it fires right up, but for 5 or 10 seconds if you try to drive off it will miss slightly just for a split second then be fine. If you rev above idle even for 5 seconds after startup it won't stutter on drive-off at all. I've replaced coils, plugs, oil filler tube, checked all clamps/hoses/intake plumbing, cleaned the MAF and throttle body, and can't turn anything up. Watching with an obd2 reader all trims and values look normal. Does it at any ambient temp, only on a cold engine, on any gas I've tried. Good. Luck.

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One possibility is a leaky fuel injector. Another member "Sean" something (don't remember) had similar symptoms. Basically extra fuel leaked down to the cylinder when the car is parked and the rich mixture causes the cold start shudder.

Update: It is NOT the AOS. Just picked it up from the dealer where it had its AOS replaced and it shuddered twice on cold start. I hope to have the dura on it this week. That fuel injector theory is sounding good.