911 3.2 stalling occasionally

[dave99]

Hi,
My 3.2 litre 911 stalls occasionally.
Idle is a little erratic. The car idles at about 800rpm and will definitely cut out within 2 minutes of running.
Some Guys here have steered me towards the DME relay. I am going to buy one of these but are there any other reasons for poor idle?
All plugs are firing and it runs well under load.
Thanks in anticipation,
Dave

[rusnak]

I would start with checking the fuel pressure. If you can get it to run, then check the fuel pressure with a gauge. Should be around 29 PSI. If it's lower, then you might have a fuel issue.

[rusnak]

Also, 2 mins is about the time it takes for the 02 sensor to heat up and then go into closed loop. I wonder how old your 02 sensor is, and also what the baseline AFR is set at. If the fuel pressure is ok, then I'd go on to check the air fuel mixture, etc. And when it quits, can you verify spark?

[dave99]

I will fit a gauge to fuel pressure first and then see where to go....
Thanks for that,
Dave

[Discseven]

Fuel filter.

[E Sully]

From your other thread, it seems a lot of oil passed through the intake. How well did you clean out the throttle body and intake manifold, and what do the spark plugs look like?

[dave99]

Thanks All,
The car has a sketchy service history so I can't say when these components were changed. It may be no harm to change the fuel filter and the DME relay as a precaution. She is running smoother after a few runs, but backfires on deceleration (always has done...)

I would like to get her back to where she should be but have limited resources.....

Thanks,

Dave

[DRACO A5OG]

Originally Posted by dave99

She is running smoother after a few runs, but backfires on deceleration

So you swapped the fuel filter and relay?

As far as back fires, do you know if you have a cat by pass?

[dave99]

I have ordered the parts but they have not arrived yet.... I am away for the next two weeks so there will be nothing happening 'til after then...
The car has no cat installed as far as I can see....

[dave99]

Hi All,

Ok, new air and fuel filter fitted, new spark plugs too....
Idling at 500RPM and sounds a bit lumpy......

Still backfires on deceleration and occasionally cuts out, I thought she was overfuelling but plugs are straw brown.

What would you do? DME relay or fuel pump? Or tune up?

Thanks, sorry for taking time getting back, only received parts today!

Dave

[rusnak]

Your idle is way way too low. I would probably re-set idle, and check fuel pressure as a start.

[JAR0023]

Originally Posted by dave99

Hi All,
Idling at 500RPM and sounds a bit lumpy......

Still backfires on deceleration and occasionally cuts out, I thought she was overfuelling but plugs are straw brown.

Dave

84-86 3.2 idle is 780rpm and a but lumpy. 87-88 3.2 idle is 880 with a little more timing. Smoother idle, also. Knowing which year chip/DME you have will help set your idle. Idle is controlled by the DME computer. The ICV will open or close to match this preset idle speed based on how you set idle screw on the throttle body. When you have the idle set just right there will be no step up or down when you pull the jumper wire.

Are you getting true backfiring on deceleration? Sounds like it's more burbling and popping. Make sure you get your foot all the way off the accelerator. The first couple of millimeters of throttle travel at the throttle body engage and disengage the idle switch and idle fuel maps. This is before the throttle plate opens. If your switch is working and you get your foot all the way off you should not have burbling. If you pay attention and play around with this a bit you find you can make this come and go at will. An exhaust leak will exacerbate the situation. Removing the cat makes the sound louder for sure.

Is your stalling at a flat idle or when the revs drop as you lift off the accelerator? If revs are dropping to nothing and our stalling when you cut the throttle search here for sub-idle dip. This is usually an indication of a lazy ICV. Some folks have had luck raising their idle to compensate. The DME is supposed to catch the revs around 1k in this situation and slow the fall down to idle. If the ICV is old or dirty it won't move quick enough to catch the falling revs.

As a tangent my wife and daughter and I spent a couple of weeks in Ireland and Northern Ireland in 2011. Absolutely beautiful country and everyone we met couldn't have been nicer. We'll definitely be back for another visit.

Good luck. -J

[Jcslocum]

Maybe a head temp sender?

[Rodsrsr]

It sounds like almost a 100% vacuum leak. You need to dig in there and check every line to see where its coming from. Jar0023 says ICV and although unlikely it could be possible that its not closing all the way, but this would cause a substantial vacuum leak, and I doubt it as this is a very durable piece. Whatever you do, dont just start throwing parts at it. If the DME relay was bad your car wouldn't run, period. The same usually goes for most sensors. A faulty head temp sensor will cause hard cold or hot starts. If your fuel pressure was low then you would have bucking under hard acceleration (starved for fuel) Low, rough idle and popping on deceleration is indicative of a vacuum leak. Check all the lines on the rear of the intake, these are usually the culprits. Thats why your idle is so low.

[dave99]

Hi All,
Really appreciate your advice, I feel absolutely sure that one or more of the examples above will sort out my problem.
I will keep you posted on the outcome....
Ireland is a lovely place and there is no better place to be when the 911 is running well and I have wind in what is left of my hair! Please look me up when you visit, I am in Kildare, the home of horse racing... I know little of equestrian sports as I am a petrol head!

Again, BIG time appreciate your input.

Dave

[dave99]

BTW, I have previously looked for vacuum leaks but I am not sure whether all the pipes are going to the right places. Nothing in the manual about the vacuum system. Anyone got a component assembly!???
Go raibh maith agat,

Dave

[JAR0023]

Originally Posted by dave99

BTW, I have previously looked for vacuum leaks but I am not sure whether all the pipes are going to the right places. Nothing in the manual about the vacuum system. Anyone got a component assembly!???
Go raibh maith agat,

Dave

There should be a schematic on the engine lid. There are plenty of good photos if you search here, but it can be a bear to search them out. -J

[rusnak]

Dave, check the pipe clamps, and hose ends for cracks. Use a strong flashlight, and run your hand along the hoses to check for splits. A common source of vacuum leaks would be the intake gaskets, especially if the intake runner bolts in the heads are loose. A quick but not 100% check would be to let the engine get warm, then at idle, remove the oil cap. The rpms should drop momentarily then recover to normal. If not, then you might have a vacuum leak. You will have to remove the air cleaner box and afm to check the crankcase breather hoses. Check the small hose going from the ambient air valve near the oil tank to the intake boot near the throttle body.

[Jprovence]

I recently battled a similar problem in my 87 3.2. I felt the fuel pressure was marginal when checked it and replaced the pump and clocked the AFM up a tick but the problem still existed. I kept smelling a rich exhaust and I have no cat, but felt it was a more than normal. The CHT tested OK, but I replaced the head temp sensor and the problem was solved (the replacement involved a drill and a lot of patience, but that's another story). Runs better now, no rich smell, etc.
A week later it died and wouldn't restart...that was an unrelated failure, DME relay!
While I love my 3.2 I really hate the first generation of DME's. With no stored fault data you can really chase your tail on intermittent sensor issues.

[BE911SC]

Originally Posted by Rodsrsr

It sounds like almost a 100% vacuum leak. You need to dig in there and check every line to see where its coming from. Jar0023 says ICV and although unlikely it could be possible that its not closing all the way, but this would cause a substantial vacuum leak, and I doubt it as this is a very durable piece. Whatever you do, dont just start throwing parts at it. If the DME relay was bad your car wouldn't run, period. The same usually goes for most sensors. A faulty head temp sensor will cause hard cold or hot starts. If your fuel pressure was low then you would have bucking under hard acceleration (starved for fuel) Low, rough idle and popping on deceleration is indicative of a vacuum leak. Check all the lines on the rear of the intake, these are usually the culprits. Thats why your idle is so low.

New intake gaskets and spacers solved the minor idle and drivability issues I was having with my 60,000-mile 3.2. Had previously changed the O2 sensor (60K-mile replacement item) and performed a full tune-up, both of which helped, but the intake gaskets/spacers really helped. To determine whether they were the culprit we sprayed water on the intake runners at the heads with engine running and one hole seemed to draw water and stumble the engine slightly so we did the intake/spacers.