peavynation

I didn't find anything searching previous threads.

2001 C4, 58k miles, new tires, original clutch but have felt no slip or shifting issue, commute is 2 miles each way (engine barely get's to operating temp).

Every so often (1 out of 15ish times) the car will shudder when accelerating from a stop to a roll, or when engine is under low rpm load (accelerating out of a intersection corner in 3rd). The shudder is very periodic, in that it feels as consistent in it's shudder as trying to spin the tires on wet pavement and having the PSM (or whatever) kick in and modulate the brakes. It's not as harsh as that, obviously, but very consistent in it's on/off of power. It almost feels/sounds like something is cutting in and out. The car has very little power during this time, but will still accelerate a bit. It will usually go back to normal power and no studder after a couple of seconds. Clutch is strong. I can't make the studdering happen consistently, even when trying to lug down the engine in 1st, giving it little gas while letting out the clutch. It just feels like a normal, lugged engine. Then when I'm taking off from the next light, it'll happen without call or reason. This happens both hot and cold, but probably more at cold if I had to pick one.
Since the car barely reaches op temp each day, could a build up of moisture on some sensor be a cause? I plan on taking it out at least once a week for a cruise and some higher RPM driving; that's the downside to a short commute, it's less fun to drive the Pcar.

Anything I should check first?

seanmcr6

(accelerating out of a intersection corner in 3rd)

You're kidding, right?

peavynation

I *KNEW* I should have explained myself, but thought I was getting too wordy already. My second gear syncro is going out and downshifting into 2nd will grind unless the trans is warmed up. Up-shifing is no problem hot or cold. Rebuild is coming soon...
I'm pretty gentle accelerating out of third though and not on it real hard.

Macster

'too wordy'? What's that?

Anyhow, does the shudder or studder feel like it is the engine protesting or the drivetrain?

3rd gear around a corner might not be too low an rpm. These engines are pretty tractable down low -- as long as one is reasonable in his expectations. My experience with my 02 Boxster is I can drop rpms down to 1K in 4th and neither the engine (nor the drivetrain) protest, though I don't give the engine the big whip when it is running at 1K in 4th. But it will take some throttle without protest.

Do you let the engine warm up at idle a bit before driving off? I find my Porsches are a bit more tractable if I give the engine some warm up idle time. Generally I let the engine idle until the secondary air injection system shuts off.

What you can try is next time start the engine the same way, and take off and drive the car but take another route and let the engine get warmed up then go back to your staring point and drive your normal route and see if the studder happens.

It occurs to me too if you're only covering a few miles per day that gas might be getting old and stale and even during some times of the year possibly gas blended for another season. Stale or seasonal gasoline run in the wrong season can make an engine act up a bit.

Be sure you buy gas from a busy station and since you do not drive the car that much you might consider filling up the tank only when it gets down to a quarter of a tank and then only half filling up the tank to keep the chances down the gas will go stale before you burn it.

Another thing to consider is running a bottle of Techron through the gas tank -- follow the directions on the bottle -- to see if a bit of fuel system cleaning helps. With short trips and the heat soaks that follow the injectors may be getting dirty, their nozzles, and the spray pattern affected which can affect the engine's combustion.

Lastly, after a proper warm up -- getting the engine up to full operating temp and having it there for awhile -- the engine might then benefit from an Italian Tuneup. Take it out and run it up through the gears a few times. Take a nice drive (50 miles or so) at highway speeds somewhere for lunch on Saturday say.

Sincerely,

Macster.

Jake Ok

If you are using an aftermarket air filter that needs to be oiled, it could be the MAS...mass air flow sensor.
I have s smilar problem in the low rpm 1st & 2nd gear, usually happens when I come to a slow down to lift off pedal, back on pedal the car stutters a little. Not sure what it is either but that is the first thing I was told to check.

peavynation

Thanks Macster. Well, when I get wordy I just babble, you're posts contain huge amounts of useful information: Peavy = Wordy, Macster = Useful Information.

Yep I do let the engine warm up a little before I leave, and all because of your advise I read a couple years ago, which you said here too: I wait until I hear the secondary air pump shut off and the RPMs drop a bit.

I have noticed that the engine will do the studder even when warmed up a bit, but I will take some solid data and log when it happens and under what conditions.

I buy gas from Costco, which here in So Cal is a mad house of lines of cars around the corner unless you get there at the right time, so I'm pretty sure it's fresh. But they do add a percentage of ethanol, which I'm a little worried will slowly eat away at some of the fuel system rubber pieces that weren't designed for ethanol's rather harsh characteristics. But such a small amount I doubt would hinder the computer's lambda calculation of the air/fuel mix and cause the studder.

I will definitely try the Techron and the Italian Tune Up. Tune Up once everything is very warm, of course.

Jake OK: everything's stock on the car, so no oily filter to worry about. But Maybe I will give the sensor a squirt of cleaner for good measure.

Macster

You are too kind.

'supermarket' gas may be fresh but a UK fuel test found supermarket gas varied in quality because the supermarkets used a variety of gasoline distributor sources.

My best results have been using Shell or Chevron or one of the top tier gasolines.

With my 02 Boxster when I use for instance Rotten Robbie or USA Gas (as I sometimes do when gas prices climb into the stratosphere since in times of high gas prices the cost per gallon at these stations can be way cheaper per gallon than at a name brand station) the check engine light is quicker to come on. The problem is a worn out converter but gasoline still plays a role.

Up to you but I'd suggest you switch gasoline brands. You can still get fresh gasoline at a name brand station. I seek out a name brand station that has reasonable prices. They exist. For instance there is a Shell, Chevron, a Union 76 and one or two other stations all within a block or two of each other and I have found gas station density works to keep the prices down vs. a station off all by its lonesome.

The station will move the gasoline. If you catch a fuel delivery truck there ask the driver how often he delivers. Some stations can get a delivery every day and I found one Shell station in Olathe KS (off of I-35) that received as many as 4 deliveries per day.

Oh, my info is while ethanol content can run up to 10% almost all refineries have kept the ethanol content under 10% at around 7% max.

In CA you'll be hardpressed I think to find any gas sans ethanol. My experience is while we are limited to 91 octane at best the better brands of gasoline are pretty good.

Sincerely,

Macster.

logray

LOL, you know what the owners manual says? Don't idle on startup and take off as fast as possible. Read this again the other day. I take a healthy compromise and bumble around a little before "taking off" and usually by the time the SAI pump quits I'm barely just rolling at 2-3k RPM max until it warms up some.

As for gas if that's what everyone is suspecting, for kicks try some really quality gas - if you can find it where you live 100 octane - and see what happens.

j beede

Sunoco 110 is available wherever there is kart racing. FYI: racing fuels tend to be leaded.

SSST

One of Macster's more concise posts. It's hard to say what the problem is, but corners in 3rd is a possibility depending on speed.

The other thing you didn't discuss was your tires. If you have changed wheel and/or tire sizes with the AWD, your PSM might be acting up in some circumstances. It can be sensitive to diameter differences between front and rear.

Pac996

Could be you don't have the car waxed enough to slip down the road easier.

Lugging the engine down? I'm sure the ignition advancement isn't like the old cars I origianlly worked on but a vacume leak can throw of some sensors where it could be altering your timing or other things to cause the stutter. Commonly a too advanced ignition for the rpm gives the stuttering you discribe. I'd also try new fuel refresh. It wouldn't be the first time a gas station sold junk fuel.

logray

I'm not aware of the 100 octane "racing fuel" available at some stations such as Chevron or 76 as having lead... the 110 stuff you find at a track probably.

Anyways...

Here's a website listing consumer stations in San Diego that have or had it.

http://www.davebarton.com/Unleaded_Racing_Fuel_in_SoCal

Reborn996

Could this also be worn engine mounts? I know mine tends to shudder a bit lugging at lower RPM's and my thought it is the motor mounts being worn that are causing the engine to move at low RPM.