1974 911 2.7L with 2100rpm idle? What's wrong?

[Karl_W911]

Not sure if I'm beating a dead horse on this problem, I'm new here and I guess this is a good way to start off. I was also recommended this site by a nice fellow on Rennlist.

First off, an intro. As you can tell, my name is Karl, I'm 18, have an affinity for Porsche that goes back to my childhood. There are currently 4 P-Cars in my family: My dad has a '74 911, and my uncle has a '76 911, an '85
.5 944 and either a 993 or a 996. The 944 was supposed to be my new car but I now have a '14 Focus ST. The 911 is my dream car and one day I'm hoping my dad will let me drive his...

My Dad's Porsche

My Uncle's Porsches


Anyway, During this winter(we live in Michigan), I've been tasked with starting up our 911 to let it run and heat up to operating temperature over the course of 30-45 minutes at a time, at least once a month. Normally it would jump between 900-1100 at the start then settle in at 1000-1100rpm. On this last start-up, I used my regular procedure, pulling up the throttle choke to give it more gas rather than pumping the gas peddle. after about 20-25 minutes it, it warmed up to about 140 and jumped up to 2100rpm on it's own; without me being in the car or applying any throttle. After 5 minutes, it didn't settle back down to 1000-1100 like before so I shut her down for a minute, then turned her back on. She went back to a regular idle between 1000-1100, but as soon as the peddle was lightly pressed, it went back up to 2100rpm.

I know that it's better to try to drive the car around the block to allow it to properly warm up, but he won't let me drive it, he has very little time to drive it because apparently motorcycles are more important and he drives the 911 roughly 4-6 times a year when the weather's nice...

Here are some videos of the problem:

Starting up with throttle up after 45-minute warm-up
https://www.youtube.com/watch?v=Eui_kOaCOIs

Starting up with throttle down after 45-minute warm-up(gas applied at 0:22)
https://www.youtube.com/watch?v=TL7m0Fu1Jog

I can't find a direct answer to this one, but I'm assuming it might have something to do with a sensor, or throttle linkage or throttle body, or vacuum leak with the CIS?

I'm hoping to get some proper education on Porsches from here that'll help me with the current family and will maybe help me one day when I get my own.

Thanks!

[Karl_W911]

Is it too soon to "bump" this thread?

[tonythetarga]

First of all, welcome to Pelican. I don't have a direct answer to your problem but I did a quick search (upper right) and plugged in 'fast idle' and there are a bunch of threads that came up. You might want to start there and see what might apply and then start zeroing in on your problem a bit more. It has been awfully cold all over this year and maybe it could be cable or spring related or maybe it could be air leak of some kind due to something shrinking or breaking from the cold.
These cars are fine if you leave them alone for the winter. Take the battery out or use a battery tender. It is best if you have fuel stabilizer in it at all times if it only sees that little bit of use.
Good luck researching and getting the thing back in running shape.

[Karl_W911]

Originally Posted by tonythetarga

First of all, welcome to Pelican. I don't have a direct answer to your problem but I did a quick search (upper right) and plugged in 'fast idle' and there are a bunch of threads that came up. You might want to start there and see what might apply and then start zeroing in on your problem a bit more. It has been awfully cold all over this year and maybe it could be cable or spring related or maybe it could be air leak of some kind due to something shrinking or breaking from the cold.
These cars are fine if you leave them alone for the winter. Take the battery out or use a battery tender. It is best if you have fuel stabilizer in it at all times if it only sees that little bit of use.
Good luck researching and getting the thing back in running shape.

Thanks! I'll do a little more searching then. We have a battery tender with it at the moment; it's a little funny and tragic at the same time, because I was taught to let cars like this run in the winter to have the fluids warm up and not freeze over during the winter...

[manbridge 74]

Take it out for a good drive before anything else....

And have a fire extinguisher within easy reach. Not that it's likely to catch fire, just good old car 101 stuff.

[Karl_W911]

Originally Posted by manbridge 74

Take it out for a good drive before anything else....

And have a fire extinguisher within easy reach. Not that it's likely to catch fire, just good old car 101 stuff.

Ok I guess I'll go find a fire extinguisher for the car before it's driven... I reckon taking it for a drive should point out any faults or issues?

And If I could drive it, believe me, I would take it out for the best possible drive I could give it; if only I could convince my dad to give me that chance to drive it!

I mean, is there something special about the '74s that he won't let me drive it? He told me I'd burn out the clutch, but I've proven to be quite good with a manual the couple of days I've been driving my ST around town. I've heard some things about the 915 tranny and how to drive it like it isn't a race car; that is to say don't drive it hard. But is there anything else I should know about the '74 cars? Anything or any reason he should let me drive it once? It deserves to be driven more than 5 times a year and in the summer, I could drive it every day if he'd let me; I've got THAT much time even with school and work! These cars are meant to be driven and it's my dream car! I deserve to be able to drive it once in life! you never know how much time you've got!(sorry for the rant, I just wish I could drive one... )

[74-911]

Originally Posted by Karl_W911

I mean, is there something special about the '74s that he won't let me drive it? He told me I'd burn out the clutch, but I've proven to be quite good with a manual the couple of days I've been driving my ST around town. I've heard some things about the 915 tranny and how to drive it like it isn't a race car; that is to say don't drive it hard.

The '74 is no different from any other 911 with the 915 transmission (used from 1972 until late 80's) when the G50 came out. True, it isn't the slickest shifting 5 speed around but with good bushings, shift coupler and if well adjusted it does the job. I'm not sure exactly what "driving it hard" means but you definitely want to avoid "speed shifting" (or whatever you call it) between gears (particularly 1st and 2nd) as that is how you can end up needing very expensive rebuilds in a hurry.

IMHO, for whatever the real reason is he is using the clutch/transmission as an excuse to not let you drive it.

This is my personal opinion but as others suggested, I would put stabilizer in the gas, disconnect the battery (put a maintainer charger on the battery) and let it just sit over the winter rather than occasionally starting it and let it run for 45 minutes to warm up to operating temps.

[boyt911sc]

Originally Posted by Karl_W911

Ok I guess I'll go find a fire extinguisher for the car before it's driven... I reckon taking it for a drive should point out any faults or issues?

And If I could drive it, believe me, I would take it out for the best possible drive I could give it; if only I could convince my dad to give me that chance to drive it!

I mean, is there something special about the '74s that he won't let me drive it? He told me I'd burn out the clutch, but I've proven to be quite good with a manual the couple of days I've been driving my ST around town. I've heard some things about the 915 tranny and how to drive it like it isn't a race car; that is to say don't drive it hard. But is there anything else I should know about the '74 cars? Anything or any reason he should let me drive it once? It deserves to be driven more than 5 times a year and in the summer, I could drive it every day if he'd let me; I've got THAT much time even with school and work! These cars are meant to be driven and it's my dream car! I deserve to be able to drive it once in life! you never know how much time you've got!(sorry for the rant, I just wish I could drive one... )

Karl,

If your Dad won't let you drive the car, why do you think he would let you tinker it? Most people I know would gladly share their beloved earthly possessions with the family members including delinquent children. I have three adults children and had encouraged them to participate in DE (Driver Education) with me. The experience and bonding is priceless. This would be a good time to demonstrate to your father that you are a responsible and dependable individual. You don't have to ask him to trust you. Trust is earned and you'll get it.

I don't know a thing about you except that you took initiative to solve a problem (if any). First thing first, if you are allowed to work on the car, I'm willing to assist you in my limited capacity. Wish you the best.

Tony

[tonythetarga]

If the car has been sitting and rarely driven I would question the ability to stop the car with the brakes. Before you or anyone drives the car, at the very least, the calipers should be examined for function and whether they are not seized and able to clamp the rotor. Then I would perform a full 4 corner brake bleed with a power bleeder and not the pedal push method as you will likely damage the master cylinder seal (the O-ring) by having it travel outside the normal travel pattern as pressure will be lost when the bleeder is opened and the pedal goes to the floor. Spray some PB Blaster on the bleeder valve and let that soak in too.

[jpnovak]

Karl,

First some Car 101. If the idle is high this means too much air is getting into the system past the throttle body.

Now some CIS 101. CIS is the Bosch Continuous INjection System that provides fuel. Air comes in past a throttle plate and then pushes on a large metering plate. The more air that comes in, the farther the metering plate moves, the more fuel is added to the engine.

Since you did not describe that the engine is hard to start or runs really poorly when started and at high idle I will start with the throttle valve.

You described that the idle goes high when you push the pedal. This indicates that the throttle is sticking and that the throttle is held open. Next time this happens, open the engine bay and reach around the left (driver's side) of the engine behind the airbox. You will feel the throttle body as a large metal cylinder on the top of the injection system. wiggle the linkage and see if you can return the idle to normal.

The throttle body could be gummed up from sitting. The linkages could have bad bushings. I woujld guess that the linakage at the transmission bell crank is about done and needs to be replaced. The other place could be that the pedal cluster bell crank needs a new bushing.

Of course, it could all be as simple as the carpet has shifted and this prevents the gas pedal from returning to normal position.

Anyway, check this out on your own and then describe to your father what you found and that you hopefully fixed it. Going above and beyond the scope of just starting the car to warm it up is what earns you the respect to be able to drive.

[Karl_W911]

I almost forgot about the initial startup! I'm not sure if I'm accurately describing this, but when the car actually sustains an idle from a start up, it sounds awful. It sounds like something is grinding or something like that. After about 10 minutes, that sound does go away and it goes back to sounding smoothly. I reckon that's the rough running and hard startup you're referring to?

Also the last time we drove it was November and it performed as well as any other time. I notice now that the rubber pedal part is a bit wobbly, moving from side to side.

I should also say I haven't actually fiddled with the car yet; I simply do all the winter care and TLC I can year round when or where he can't. And of something goes wrong, then I write it down and keep track of it and tell him.

I'm gonna have him take it to the closest Porsche mechanic that isn't a dealer in May when the insurance goes back on it so they can do a full inspection.

But before that, he hasn't said that I cannot work on the car, and I'm willing to get my hands and legs dirty to work on this car because it's worth it. I'll need some instruction as I've never wrenched on a car before, but I'm ready to work and learn!

[dfhtrhjn]

The car starts nicely, looks like your cold start valve works. I'd check the throttle linkage as suggested in the previous post first.

As a general rule, fuel deteriorates after a few weeks without stabilizer. Before tearing anything apart, I would dump a bottle or two of the Redline fuel system cleaner and run a tank through the car.

I think you'll have an easier time identifying your problem with the fuel system cleaned a little, and a fresh tank of gas.

[fintstone]

Sounds normal to me. With the throttle manually held open with the lever, the car will always run faster as it warms up.