kj217

first of all,, i want express how glad i am to be here in RL,, i thank you all for the great help and support that neither my local dealer nor local P owners seem to provide,,

back to subject,, i have tried the e-gas recalibration many many times,,

what are the major car-battery connection points??

one more point,, the car at cold start doesn't shout and jump to higher rpm as usual,, it starts lazy up to the regular rpm level as if it is warm already,, rings a bell?

Macster

Well, the lazy sort of start cold -- which is kind of one half the symptom (the coming back up to normal RPMs half) -- sans any backfiring or stumbling -- which means the fuel mixture is right which to me eliminates fuel pressure, fuel supply, air temperature, coolant temperature as being wrong -- sort of suggests...

Nothing.

That is at first I thought there might be something signficant and there might be but what means?

Check that. Symptom might arise from the "bad" battery putting a heck of a load on the alternator; or going with the wiring theme a bad battery/car connection somehow accounts for this behaviour. No time to detail this.

It could still be due to a faulty E-Gas pedal or throttle body controller module.

And there are probably more possible causes.

The major battery/car connection points are the battery terminals and the other end of those cables where they connect to the car, chassis, or wherever they connect.

I've seen such poor condition battery cables that the battery cable where is connects to the chassis is so frayed/corroded that just a few strands of copper carry the electrical load and these can glow red when the starter spins the engine. This heating up and sudden cooling tends to soften the copper which makes it less likely to break so this condition can continue for a while until one or more strands finally does break and then the heat melts the others.

(Years ago when I replaced battery cables -- when they were much less complex -- I'd buy heavy duty welding cable instead of regular battery cable --cause welding cable carried more current: Cable was larger in diameter and had more strands.)

Starting at the battery you'll have to trace the battery cables to where they go and to what the connect to and make sure not only the battery terminal connectors are good and corrosion free (which is usually the case cause they're "easy" to get to) but the connections at the other end are likewise. Since these are less accessible they tend to get overlooked.

Is the battery in good condition? Can you have an autoshop or even a battery reseller check/test the battery for you? Check the battery acid's specific gravity level for you?

Sincerely,

Macster.

Pac996

You might try checking major connections (big plugs and sockets) for electronics in the engine compartment and the grounds in there if they are findable. One guy was having rpoblems that turned out to be a connection on his alternator. Might finger some of those wires.

I just bought a durametric last night. Hopefully I wont have something like this presenting problems later on. Anyway good luck.

kj217

an update..
the humming sound that goes with the symptom is produced from the fan of the passenger side radiator,,
it is to me a chicken-and-egg issue now :S
does the fan drain more amp then rpm drops??
or,, rpm drops then fan is suffering from that??

the dealer promised to arrange for a used throttle body to test on my car tomorrow,,
i will keep you updated,,

Macster

Hard to believe the radiator fan could consume so much power as to cause the alternator to pull the engine down that much to keep the alternator turning.

Besides the engine controller/E-Gas control module would attempt to keep the rpm constant. This to me at least puts even more suspicion on the engine controller or the E-Gas control module.

The latter more easy to replace, test, and much cheaper (I think) to replace should it prove to need it. You can of course replace the engine controller but as with most Porsche components you want to make darn sure the diagnosis is spot on and replacement is absolutely necessary and of course some WAG by a 'net expert, even a well-intentioned one is not such a diagnosis.

My 02 Boxster's fans make noises sometimes and the idle's just fine, constant with no dips or falls. (Only barely related: In fact I found the other day the driver's side fan not running. About the same time I noticed this the coolant tank decided to split. Both fixed now. Fan problem was a low speed resistor. The coolant tank of course had to be replaced.)

I don't recommend it but you could disconnect the fan electrically from the car's wiring harness to of course not only disable it but eliminate the possibility (as slim as I think it is) that the fan is somehow causing the electrical load on the alternator to cause the rpms to drop/dip like they do.

Now a Porsche tech with the PST2 can command the fans to come on low or high speed and independently of each other and the engine running.

If the fan causing any problems with excessive power consumption doing this and monitoriing the load on the battery should make this evident.

Let's see what the throttle body/control module swap out produces.

Sincerely,

Macster.

kj217

there is a part "electronic throttle control" located under the dash in the driver side,,
what does this do?
could it be related to the symptom?

kj217

after all,, issue solved by replacing the fuel tank breather valve,,
it wasn't releasing air when pressure builds up in the tank,, which was causing instant fuel cut-offs,,
the whole thing cost $200 @ the dealer,,

rb101

Interesting outcome, can you send the part numbers they replaced. Mine kind of does the same thing, just not nearly as bad as yours did.

Thanks

Rick
99 996C4
87 944S

philooo

Hey do you know, where is that valve ? and what it looks like ?

I think I isolated my problem of start in the morning. It seems the engine burn the fuel that is in the gas line, but then starves. And after waiting like 30 minutes it then works just fine. I assume that valve problem would make sense as it might be clogged and release the pressure once I wait long enough.

I'd love to check it out if I knew where it is located

could it be the thing located in the top left corner of this picture, you can barely see it , but there is a breather valve under there.

last thing, as you can see my gas pump 'screw' is glue down... is that a normal thing to do to secure it ?

TomF

Just as a follow up to this, there is a detailed DIY for this replacement procedure over on Renntech...

jlaurent

Hi TomF
Hi searched the link of this DIY but didn't found anything...
Thanks for your help.
jLaurent

jlaurent

Hi KJ
I'm owner of a MY '99 C4 and I have to face with an idle issue for 3 or 4 months. I tried to understand myself, I let the car to a tech and no result. I thought to an air leak nearby the air intake collector when I just read your thread :-)!
Could you please telling me the ref of this breather valve?
I do think I have the same problem as yours.
Thanks a lot for your response.
jLaurent