So I got my 1970 1.7 still injected finally ready to drive. It starts right up with and runs fine, for about 20 - 30 seconds, then it starts to idle rough. The idle will drop to almost 0 then surge to about 1500 - 2000rpm. If I slowly roll onto the throttle it revs up, but if I quickly press the throttle it stumbles and almost dies then revs up. I am going to get a vacuum gauge soon and check for leaks using the method in Tech Tips 700. Anybody have any ideas of what to look for? Could it be something other than a vacuum leak?. I have done a valve adjustment, replaced points, rotor, cap, plugs, injector seals. Still have not checked timing or dwell. I will also double check the MPS.

So after it warms up it runs a little better. RPM's not dropping quite as low and not surging quite as high. Also, it does not stumble when I punch the throttle after it is warmed up, but after I punch it the idle drops almost to the point of dying.

I changed all the vacumn hoses, intake gaskets, injector seals, and the little angled hoses to the injectors, set the timing and dwell properly, adjusted the valves and went for a drive. What a difference, not the same car, smoother, quieter, more power and idles at 900 like it is supposed to. The more I drive it the better it seems to get, keep at it and you will find your problem, a good rule of thumb that has worked for me is do the simple stuff first, if it still isn't running well at least you know what it isn't and you haven't wasted any money. My .02 worth.


Ian Stott
Moncton
Canada

Ian,

Glad to hear you worked through the problem. The vacuum hoses were likely the problem with the stumbling as it sounded like a mixture issue.

Sorry we didn't chime in, but you needed no help.

Congrats and post a pix of the car!

So I took my car on the road tonight for the first time EVER!! But, I am still having problems. The car still has a fluctuating idle, still need to check for vacuum leaks. Also, it stumbles and seems to miss at high rpms under load. I tried to adjust the timing but I am confused. I am using the method in the Porsche 914 handbook. It says to check timing at 3500 rpm. When I do this the mark for #1 TDC is no where near the notch on the fan housing. It is close to it at idle but not at 3500 rpm. Am I doing something wrong here? Could this timing issue be causing the high rpm stutter? Would a vacuum leak also cause this stutter?

I might have answered my own question about setting the timing, so don't worry about that, but I am still wondering about the stuttering. I will recheck timing properly tomorrow and let you know how it goes.

I did not quite get to the timing tonight with the amount of time I had. I did replace the coil with another one I had that I know works well, I checked all of the vacuum lines and they are all in pretty good condition, but I put hose clamps on them for good measure. Also I found that the vacuum line that goes into the big black elbow for the air cleaner was pretty loose. I reattached that with a little jbweld to help seal it up. I will get to test it out tomorrow and check the timing.

What I meant by this is that there is a fitting that a vacuum hose hooks up to. This fitting was very loose, so I reattached it.

You have the same problem my car had. I had the same symptoms yours has now. I bought a 1.7 that had been sitting a while. I replaced all the vacum hoses just for good measure..... still did the same thing. After further inspection I found that the elbow that goes from the air cleaner to the trottle body was cracked in several places and just as you had found, and I used some Black RTV to seal it. The car ran ALOT better after that but still hunted like yours does. After awhile it got worse and I started to look other places. I found it. The intake boots were leaking pretty badly. So I ordered some and replaced the injector seals while I was there. Car runs great now. Some info about the 1.7 that I was told by George Hussey... that the stock intake runner boots for the 1.7 are slightly smaller than the 1.8, and they don't make the boots for the 1.7 anymore, so...... you should put clamps on the boots. I didn't like the idea cause it doesn't look like factory but did it anyway. Don't know if anybody on the board has ever heard this though.

For the miss... that could be alot of things. My quess would be electrical.. spark plug wire or possibly an injector wire... just a blind quess.