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Hey guys,
My 1986 944 Turbo is in great shape. All brakes, suspension, paint, hoses, filters, have been gone through. The motor has roughly 165,000 on the clock and has come out for a complete reseal job about a year ago. All is stock including the original turbo with the exception of a 3" exhaust and AC delete and cup mirrors . I have no complaints while driving the car and the temperature reads dead center once the car has been operating for 15 minutes.
My only gripe is the extreme shuttering/shaking and vibrating in the cabin during a cold startup. Last I started the car from cold it was roughly 70 degrees out. After 1-2 minutes the car settles down and is smooth. Motor mounts are about a year old as well.
Is this to be expected from a 33 year old car on startup? Or is something off? I was thinking of replacing the DME temp sensor this weekend but have no reason to believe it's faulty.
Is the engine running rough or misfiring? If so could be a vacuum leak from intake manifold that seals as the engine gets hot.
You mentioned you replaced engine mounts a year ago. Were you having the same problem then? If so and you replaced them with aftermarket mounts (uro) it is time to change them again. I have never had a uro part last more then a year. Bought a lot of suspension parts for my BMW and was happy for the first several months until it all fell apart. Never again!
165K on the engine and transmission but the paint, suspension, bushings and tires are new
Engine came out about a year ago for a check and full reseal. Motor mounts were done at the same time and the invoice specifies Porsche OE mounts. Prior to the engine coming out it had a rough idle and oil leaks everywhere.
I've had the intake and fuel rail off a number of times and replaced gaskets each time but I think there may be value in checking the system for air leaks. The fuel rail is showing it's age. All vacuum hoses were also replaced so I'm confident they in good shape.
No issues overheating even in the summer and high RPMS. It's just the initial start that is extremely rough..once I drive off and on idle all is smooth. Oil pressure is good and fuel filter was replaced 16 months ago. I will definitely test the temp sensor and fuel pressure valve this weekend.
Last thought was that perhaps it's my battery? I have a lightweight Braille that is always on tender but maybe it's just not putting out the power needed on initial crank?
I'm in awe of the engine compartment itself: the stickers! Even the under-hood light fixture looks new. Well done sir.
I don't think it's the battery: for the first time ever--no joke--I left the parking lights on when I got home yesterday. What a coincidence to have a battery experience to help this thread. This morning, there wasn't even a hint of electricity anywhere, no click, no clock, not a blip--totally dead battery. I jumped with my wife's car and it barely turned over, but once it fired, it idled as usual. The voltage gauge showed the usual reading and it ran like nothing happened.
It would appear the car can run perfectly on alternator alone even after cold start.
I'm in awe of the engine compartment itself: the stickers! Even the under-hood light fixture looks new. Well done sir.
I don't think it's the battery: for the first time ever--no joke--I left the parking lights on when I got home yesterday. What a coincidence to have a battery experience to help this thread. This morning, there wasn't even a hint of electricity anywhere, no click, no clock, not a blip--totally dead battery. I jumped with my wife's car and it barely turned over, but once it fired, it idled as usual. The voltage gauge showed the usual reading and it ran like nothing happened.
It would appear the car can run perfectly on alternator alone even after cold start.
Interested in seeing the video
Thanks! Since acquiring the car I've had the self realization that I'm a bit OCD when it comes to condition and things looking tidy. The car has a really interesting story per it's CarFax history. 6 months after arriving in CA in 1986 the car was stolen, recovered and sold at a police auction and then sent to the Netherlands for 4 years. When I took the seats out I found Danish Coins (krones) buried in the carpet. It was then subsequently purchased by someone in 1996 in NJ, sold to a new owner in PA and then me. Knowing all this it's pretty amazing the engine bay is as original and clean as it is. The 951 was always my childhood dream car so when I finally got one I was determined to bring her back to life. I've had her since 2016, I'm 33 now. She's a keeper.
I've also found that investigating and doing the work yourself is much more rewarding (and frustrating)
165k on that car! The paint looks fantastic, it takes a lot of work to get a car to look that good. It is obvious this car has been given a lot of love throughout its life.
Probably not battery, old cars do not need the amount of electricity that the newer cars with all the computers need.
I'm going through the same issue right now with my car. '86 951 with ~ 155k. It is driving me nuts! Here is what I've done for troubleshooting:
-Vacuum leaks. Pressure test your system. I found vacuum leaks in some hoses, did a venture delete, replaced the ICV, & cycling valve. They were all leaking. I also rebuilt the throttle body.
-ICV can cause rough idle issues. I've jumped mine out right now and it runs smoother, but the idle is a bit higher.
-Bad/improperly adjusted TPS. If you have a leaky throttle body, the oil can contaminate the TPS sensor. (replaced mine since throttle body was leaking)
-Bad AFM can cause issues. (rebuilt mine--potentiometer was damaged)
-Bad DME temp sensor (replaced mine-cheap)
-Bad 02 sensor (unplugged it and it ran the same)
In my case, I've got something going on still with my ICV or TPS adjustment. Good luck!
Interesting we have the same year and mileage I have a consistent idle but the initial startup is rough.
-Vacuum leaks. Pressure test your system. I found vacuum leaks in some hoses, did a venture delete, replaced the ICV, & cycling valve. They were all leaking. I also rebuilt the throttle body. I also did a venturi delete when I replaced all the vacuum hoses with Porsche OEM. That was expensive! New cycling valve as well. Need to do a full vacuum leak test.
-Bad/improperly adjusted TPS. If you have a leaky throttle body, the oil can contaminate the TPS sensor. (replaced mine since throttle body was leaking) I had the throttle body out a few weeks ago to clean and rebuild with a new gasket. All seems okay there.
I'll have my video posted later today so folks can see the engine movement and view from the drivers seat. Hoping vibration is appropriately captured.
Was able to record two videos of the same startup on the links below. This was from a cold start, 73F degrees ambient temperature and the car had been sitting for 5 days.
Note that there is a lifter tick that is always present after the car has sat for at least a week but disappears after a 30 minute drive. No considerable engine movement on startup which I'll take as a good sign regarding engine mounts. Also, the interior noises are mostly vinyl interior parts but nonetheless its loud initially. Quiets down considerably after the car has been driven.
When did the problem start? After you removed intake and fuel rail? Double check your work. It is hard to tell from the pictures but look at the two areas circled. It looks like a clamp is loose in one circle (hard to tell because of small size of picture) and there is a pretty good kink in the booster line.
When you say the engine was out for a full reseal did you do the head gasket?
Head gasket was done when the engine was out. No issues after the engine job. These symptoms on initial start were only noticed in the last few months.
Good call on the kinked hose from the brake master cylinder to the intake. I was able to reposition to reduce if not eliminate the kink. The Porsche OEM hoses are pretty thick and kink in a right angle. The hose going to the banjo you circled towards the bottom is extremely tight but you're right, the clamp is loose and unfortunately wont tighten enough to grasp the thin hose. However I'm fairly confident no air is escaping since that connection is extremely tight.
I'm going to lookup next steps to do a full vacuum leak test. The intense vibrating and shaking along with the big RPM drop before leveling out around 900RPM make me think the engine is initially being starved of air or fuel.
As far as I know the fuel injectors have never been replaced under my ownership. When I've had the fuel rail off, they look fine but I haven't tested them. Given all the other work that has been done it probably wouldn't hurt to replace them altogether. I wish there were an OEM option to replace the fuel rail as well.
06-18-2019, 04:44 PM
Rough Startup
. I have no complaints while driving the car and the temperature reads dead center once the car has been operating for 15 minutes. 
