Rough idle and car dying‏

paddict · 09-02-2014, 05:21 PM

Something weird happened with my 1989 911 turbo Sunday night. I went out for a spirited drive and the car ran great. Getting off the highway coming up to a red light, I braked hard and came to a stop. While in neutral, idle started acting up, going up and down. Eventually, the battery light came up and the engine died. I restarted the car and had to press on the gas to prevent the car from stalling. When doing so, I noticed quite a bit of smoke. It drove ok until the next light and again, I had to stay on the gas to prevent the car from stalling. Decided to drive back home and went back on the highway, keeping the RPM low and staying off boost. I also noticed quite a bit of smoke when accelerating (off boost) in third gear merging on the highway. Couldn't tell what color the smoke was since it was dark outside. Again, when I got off the highway, the car wanted to die in neutral or when I had the clutch pedal pressed in. I was low on gas (slightly below 1/4), so I stopped and refilled the car. Started the car afterward and no more rough idle and stalling. No visible smoke either. Still, I drove back home slowly, worried that something could be wrong with the car.

Any idea what could be wrong? The car is stock, other than a Borla exhaust. The trigger seemed to be the hard braking, but this could just be a coincidence. Refueling and restarting the car appeared to resolve the issue, but again, this could just be a coincidence...

JFairman · 09-02-2014, 05:34 PM

Could be alot of things. One could be the rear fuel pump relay not working at times. That would leave the motor running on only the front fuel pump and the 12 volt heater element on the bimetallic spring in the WUR would not be heated and that would lower control pressure making the motor run too rich. Then it could do what your's is doing.
Not knowing the smell or color of the smoke makes it a wild guess.

paddict · 09-02-2014, 05:46 PM

Unfortunately, it was too dark to see the smoke and I didn't smell anything unusual. I'll take the car out for a drive tomorrow and see if it happens again.

mark houghton · 09-02-2014, 06:48 PM

Start with the simple and obvious....Intercooler and turbo seals. You were previously doing a "spirited" and surely totally illegal run up the 'ol rpm scale. Shame on you, to exercise the old girl that way.
Might have dislodged an o'ring or popped a vacuum line somewhere. That can cause serious over rich conditions, as can single pump running and associated WUR power issues.

As Jim already said, it's a wild ass guess at this point, but it seems the common thread when these types of complaints always start with running full on boost and all of a sudden.....crap!

oilonly · 09-02-2014, 06:49 PM

Make sure the yellow and black relays in the back have not come loose plus check the two front red relays also.

Robbbyg · Robbbyg's Garage

Check the Hose going into the Turbo ,
The one on the left side, its come loose at join and separated,
needs to be retightened,

How to-
Jack up car six inches to make it easy to reach,

Tools needed, 1 flathead or Philips screwdriver

Time needed 5 to 10 minutes

Your Welcome

paddict · 05:17 PM

Started the car this evening and let it idle a bit. White smoke came out for about 3 seconds upon startup and dark grey / black afterwards. Pretty heavy gas smell also. After about a minute or two, idle started going up and down. Went for a very short drive and at the first stop, the engine died. Exact same problem as on Sunday night.

I'll look into the fuel pump relay and potential vacuum leaks. Robby, I did look at the hoses going to/from the turbo and everything appears tight... Unfortunately, I don't think it's going to be that obvious! Still, thanks for the suggestion!

Any good reading suggestions regarding the fuel system on these cars?

xbmwguy · xbmwguy's Garage

Not to insult or anything or anybody (purists) but every time I read posts like this I get a huge grin knowing I no longer have that crappy 70s injection any more

now back to your regular scheduled program

T77911S · 09-05-2014, 04:23 AM

oh the nieve.
i was just thinking the same thing about the guy with the 3.2 that wont start when it is hot.
i wonder what sensor or electrical part is bad? oh, maybe its the wiring.

Alan L · Alan L's Garage

You can poke around at possibilities (and the list would be long), or you can start a systematic diagnosis - starting with the fuel pressures - preferably while it is misbehaving/running.
Alan

SEE YA · 09-05-2014, 08:59 PM

Maybe you have a air leak off the manifold? The engine would then suck in air, and affect the running of the engine.

DSPTurtle · 09-06-2014, 04:26 AM

My money is on JFairmans suggestion. One of your fuel pumps isn't playing nice.

delta911 · delta911's Garage

Lambda control relay?

oilonly · 09-06-2014, 06:47 AM

JMO but i think trying to diagnose these cars without an on board AFR gauge is a crap shoot, better to have an AFR than a pressure gauge even, of course having both is optimum.

paddict · 08:02 AM

Well, ended up bringing it to a mechanic and apparently my ignition coil went bad... Does that make sense, based on the symptoms encountered?

Tippy · 10-06-2014, 10:05 AM

No. It's fuel related beings wandering idle and keeping foot on throttle to maintain idle.

So, on that note, you must sell it to me since a catastrophic faulure is eminent.

Just kidding, let these CIS experts fix you up.

paddict · 10-06-2014, 10:25 AM

No problem Tippy, will sell it to you for whatever Hagerty says is a fair value nowadays!

Brought the car to THE cis expert around here, rather than going to my usual mechanic... Am skeptical now!

Tippy · 10-06-2014, 10:39 AM

Quote:

No problem Tippy, will sell it to you for whatever Hagerty says is a fair value nowadays!

Brought the car to THE cis expert around here, rather than going to my usual mechanic... Am skeptical now!

Please don't make sell my house to generate funds!

J/K

So a CIS expert tinkered with it?

It sounds lean from your description.

RarlyL8 · RarlyL8's Garage

Ignition breakdown could have those symptoms. Same can be from bad WUR or Fuel Distributor / Lambda. Did he replace the CDI or coil? Fixed?

paddict · 10-08-2014, 12:11 PM

Picked up the car today. Ignition coil, spark plugs and spark plug wire set were all replaced. CIS was adjusted and the car runs great now.

Still, I'm surprised that these parts would go bad just like that. The car was running great on the highway and just a few seconds later, couldn't hold idle. It never showed any other symptoms in the two years I owned the car beforehand.