Bustingear

I have noticed a cold start issue with my 996. It starts when cold but immediately starts to sputter drops rpm then stalls. I restart about three or four times and then it runs ruff. As it gets warmer the idle climbs up to speed and no problem.
Sometimes I force it to run by pedeling and it sputters down the road and gradually picks up rpm. If the Cars been run and I shut it off it will start back up no issue.
There are no engine lights just this issue as described? Can anyone shed light. I read a post about a boxster that had the same issue win no resolution. Suggestions welcome.

Macster

What MY car? Early 996's with the 3.4l engine and pre-eGas came with an idle air control valve and these can get dirty or just bad.

But the symptoms read like a temp sensor ( coolant or intake air temp) is supplying the wrong (too high) temp reading.

Thus the DME thinks the engine or air is warmer than it is and supplies less fuel.

As the engine warms up it runs better which suggests the coolant temp is the culprit.

Also, that it starts ok after it ran enough to get warm points to the coolant temp.

Anyhow, with an OBD2 code reader/data viewer/logger you should be able to view air intake temp, coolant temp concurrently and note at a cold start and with the symptoms present which one is reading off. After the engine sits overnight they should read about the same and should be about equal to ambient air temp.

Bustingear

So are you saying that it is the coolant temp sensor as opposed to the IAC valve or are you saying that it could also be anorther or different air temp sensor?

Bustingear

I am replacing the coolant sensor underneath and the air temp sensor on the right top of intake
These were cheap so starting there
If no improvement will try idle air control but I have already cleaned it once recently. Still no check engine light.

Bustingear

Ok replaced both the coolant and air temp sensors and no improvement.
I have now sprung for a new maf at $250 and no improvement. In fact disconnected the battery to reset and when I use the maf it will not start. I unplug the new maf and it starts and gradually runs better but ruff. Plug the new maf in and it stalls. Wow what's up? Suggestions?

Macster

As I suggested you should have used the OBD2 code reader/data logger to view the coolant and intake air temps. Noting those were ok (as it appears they were) would have saved you some money throwing parts at the symptom.

With a new coolant sensor and an air temp sensor and a MAF and the symptoms or behavior still present I'm loathe to mention any other possibilities for fear they'll trigger another round of parts being thrown at the problem.

However, I dislike leaving something unfinished if it is within my ability to finish.

That the engine runs worse with the new MAF connected bothers me. It suggests the MAF is the wrong MAF, or there's a problem with the connector or the wiring.

If you install the original MAF does the engine misbehave the same way?

Bustingear

Will check tonight

Bustingear

Maf is brand new Bosch unit 0 280 217 007
This appears to be correct for the 1999 911 996 without E Gas
I will try the old maf tonight and report back but it was acting similar prior to replacement but I'll double back
What else could cause the car to run worse when plugging in a new maf? It runs better without the new maf plugged in?..

Macster

IIRC the earlier Boxster's required a DME upgrade to accept the new MAF.

I'm not sure if this applies to the early 996's.

You might look into this unless you tell me the new MAF has the same part number as the old MAF and the old MAF is the original MAF or identical to it.

Then I would have to hazard a guess the new MAF is defective out of the box. But before you send the new MAF back for a replacement you need to eliminate other possible causes for the behavior.

Bustingear

Decided to check the idle air control sensor. Pulled I t off and cleaned it in fact. I did this six months ago. Even though it ran much better and I have found the issue. I will order a new one now that I know as well as its regulator sensor. back on the streets again!

haimiko

do you have the part numbers for both?

PORCAR

Very old post, but some good suggestions here. Only thing different with me is I once got a battery charging light.

haimiko

I cleaned the air flow sensor and fingers crossed this morning I had no cold start stall. In fact for the first time in a long time, the ECU compensated and increased the rpm a bit.
Thank you!