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porschebadger · Joined: 10 Jun 2011 Posts: 27 Location: Green Bay, WI

Yesterday my 931 received some tune-up items. New plugs/wires/fuel filter/oil change/cap/rotor.

The first start was really rough for a second or two and then the car sputters and dies.

Second start more of the same.

Third start the idle would jump and the car would sputter when I try to rev a bit.

Fourth start, the idle evened out a bit and after a drive, the idle was sitting just above 1000 and pretty steady.

I checked the forums and thanks to ideola realized the fuel filter was pointing toward the engine so it was on backwards. I flipped it and started the car up to more of the same process. Sputter and die. Sputter. Sputter and jumping idle. Slowly start to even out.

Before the tune-up cold starting was just fine. In fact I had an issue starting the car when it was warm. Any ideas of things I can be checking?

The ignition wires that I put on seemed a lot longer than the ones that were on the car so they are hanging over each other and on some other wires, not sure if this is an issue.
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- 1980 931 - Silver/Graphite Two Tone - Optional 5 Lug and Leather
- 2003 Maserati 4200 GT
- 1973 Jaguar XKE 2+2
- 1994 Range Rover SWB
- 1975 K5 Blazer
- 1996 Ducati 900SS SP
- 1989 964 C4 - Sold : (
- 1987 951 - Sold : (
- 1999 986 - Sold : (

porschebadger · Joined: 10 Jun 2011 Posts: 27 Location: Green Bay, WI

Did some more tinkering today. Yesterday while working on the car I noticed that the belts that keep the airbox clamped down had broken off, so I zip tied the box real tight.

Thinking that the air/fuel mixture might be messed up, I had my buddy who is a much better wrench take a look while the car was cold. He took off the rubber boot over the decell valve next to the airbox and if he pressed on it the stumbling idle returned to normal.

Is it possible the car got used to the loose airbox and now that its sealed up tight, things are off? Again, when the car is warm, the idle returns to normal.
_________________
- 1980 931 - Silver/Graphite Two Tone - Optional 5 Lug and Leather
- 2003 Maserati 4200 GT
- 1973 Jaguar XKE 2+2
- 1994 Range Rover SWB
- 1975 K5 Blazer
- 1996 Ducati 900SS SP
- 1989 964 C4 - Sold : (
- 1987 951 - Sold : (
- 1999 986 - Sold : (

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

A loose airbox will let soot, etc into the air intake but wouldn't affect the A/F ratio unless there was a large accumulation on the air sensor plate.

Had the car sat for a long time? Could the A/F been adjusted to compensate for a problem you fixed with the tune up?

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

porschebadger · Joined: 10 Jun 2011 Posts: 27 Location: Green Bay, WI

Thanks for the response dpw. Some more bakground info:

The car has been sitting for probably 3 years. Its been started and driven maybe once or twice a year.

In the last month I purchased a new battery and started with the tune-up items. The car had a warm-start issue in the past. I would need to crank 4-5 times and wait a minute or so between attempts to start it up.

After the recent work on the car, it did start warm a few times without issue. I drove the car from Green Bay to Madison (about 150 miles) without much of a fuss. Cruised at 75 miles an hour pretty comfortably. Cold start issue has resumed the last few days.

Today I drove the car for about 15 minutes. Parked for about 20 minutes and the car wouldn't start. Not sure where to begin troubleshooting.
_________________
- 1980 931 - Silver/Graphite Two Tone - Optional 5 Lug and Leather
- 2003 Maserati 4200 GT
- 1973 Jaguar XKE 2+2
- 1994 Range Rover SWB
- 1975 K5 Blazer
- 1996 Ducati 900SS SP
- 1989 964 C4 - Sold : (
- 1987 951 - Sold : (
- 1999 986 - Sold : (

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

You need to run a complete CIS test...system pressure, cold control pressure, warm control pressure, and pressure leakdown. The diagnostic regimen listed in Haynes is accurate, but you need to make sure you check against the 931 specs listed at the beginning of the Chapter 13 Supplement.
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erstwhile owner of just about every 924 variant ever made

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Bad WUR.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

ptheskil · Joined: 03 Aug 2004 Posts: 128 Location: Essex, UK

and/or crud, loosened during the service work, finding its way into the WUR/fuel distributor. Either way you need a CIS pressure test.
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1981 931 series2 Euro spec