RyanPerrella

ok so pre 91 dosent have any issues with shearing.

how much thicker is the shaft is it noticeable or just 1-2 mm thicker in diameter?

RngTrtl

chalk a +1 up for having an Auto-box. Hehe

Candleman

Just checked the throttle body cables and interestingly all 3 have significant slack. There is no tension in them at all. So what is the best way to adjust them? Is there a link to some photos where someone was in the process of working in this area?
My description of the lurching probably sounds a lot worse than it is. After driving it and specifically looking for when it happens it seems to happen more in the range of 700-1300 rpm, not -2000 as I had first stated.

6mil928

I have the same issue. It goes away most of the time when I floor it for a bit. It just seams to clear up. It's funny it just came back today. My car does run rich if that helps anyone. I'm planning on changing the coil it may be getting weak. I had the same problem on my 81 Trans am.

blitz928

Had a similar problem on my old s4 about a week before the LH brain failed

6mil928

Also wanted to add the fuel injection cleaner seems to clear it up. I would suspect that mine is fuel related.

Podguy

Do the S4 cars have a deceleration valve? I know the 16 valve cars have this and it will when failing cause the car to jerk and jump at slow speeds?

6mil928

Never heard of this part. Do we have any pics of it?

Gerg

Could it be..you're lugging it?

Jim bailey - 928 International

the 80-84 was fitted with a vacume limiter (decel valve) gold anodized can on the right side of the throttle body . Under high vacume it bypasses the butterfly reduces engine braking and that is perceived as acceleration by some.....same as when a race car spins onto the grass and the announcer says it picked up speed !!

Podguy

Jim,

Actually, the reason deceleration valves were added to cars was ti reduce pollution. When you let off on the gas there are a lot of unburned hydrocarbons pumped into the air. By keeping the accelerator open a little while at low speed on deceleration some of this extra gas was burned off and the car runs cleaner.

I actually thought the deceleration valve was on the 78 - 79 as well, but I would have to check that. When a deceleration valve gets old or dirty or the diaphram goes they will not function smoothly and cause the car to jump on deceleration and at low speeds. Removing them and plugging the two hoses connecting them to the throttle body will cause this symptom to go away. Of course the right thing to do is buy a new one from you. How many new ones have you sold over the years?

Now I assume the same is true of the LH system. There is probably a deceleration circuit built into the car somewhere. Since the LH controls everything then the function is probably part of the programming. I know on the old 914 the same problem was seen when the car was just warming up and we traced it down to the head temperature sensor. So if there is deceleration circuitry or programming built into the LH maybe there is some issue with the temperture sensors or some other issues with the injection system.

I do nto know the LH system well enough to tell if this is the case, but it is worth looking into. Swapping the LH, putting in a new Temp II sensor are all good places to check. Another might be the fuel dampers which I guess could chatter or be affected by a less than perfect vacuum system.

All cars are really the same when you flip them on the roof and start wacking away at them with an axe.

heinrich

LOL Dan ... the LH cars have a pop valve, ie decel valve and it is vacuum-driven off the throttle body. It's the thing that feeds into your cats. But I'm not sure it works the same as what you describe .... I think it redirects air pump excess to the intake airbox, as opposed to the cats, on decel.

Bill Ball

LH shuts off the injectors if you take your foot off the gas (if the idle switch is working) until the RPMs drop below 1400.

6mil928

LH?

Podguy

Heinrich,

The "pop" value is quite a different thing. It is just regulating air flow to the CAT for a cleaner burn. I suspect what Bill is talking about is more in line with the theory of the deceleration valve on the older cars, but I also suspect Porsche did this to improve gas mileage. On old carburatored cars you could improve the gas mileage by setting the idle to the lowest level sustainable. Then when you declerated the carburator allowed the engine to suck down less gas. It was good for a couple MPG more.

That gas gets fed back in at 1400 RPMs sounds a lot like the LH faking a decleration valve. Amazing things what they can do with electronics these days. Maybe the jumping is related to a poorly adjusted idle switch.

All I know is I am still having a hard time getting my 86.5 S4 hybrid to fire up.