Surging and jerking problem 84' 3.2L

[pk 84 911]

To add this. It may be relevant:

The idle constantly fluctuates as well, not wildly but by maybe 200 rpm. Also, at the linkage if you barely increase the rpm and hold it, it bounces around. It also dose not rev smoothly through the first 300 or 400 rpm. Am I making any sense here.
Something is just not right here.Minimal throttle pressure just does not feel right on this car.


At a slight touch of the throttle the car surges. When cruising around 40 and while slightly touching the throttle it only does it enough that the driver would notice it. But when in heavy trafic at 5 to 10 miles per hour it make the car difficult to drive. It actually causes it to jerk quite badly. You really have to work the clutch to drive in heavy trafic.

Any suggestion, Thanks

Paul
84' Cab
77' 911s rebuilt 2.7

[Jascha]

Not to worry -these are usually resolvable air (sometimes fuel) metering problems...

You can start here (if it was just idle another scheme is needed):

1. Air Flow Meter (AFM) is not recording correctly air flow values. There is a DIY way to refurbish it (search on my name for a similar thread)

2. Vacuum (false air) leak. One known offending area is from intake manifold gaskets –try to re-torque (16 -18 ft-lb !) the 12 bolts

3. Check all vacuum hoses / connectors to the throttle body...

[Nine9six]

Yeah,
Do a search...Maybe the CHT sensor...

[mjshira]

sounds like CHT sensor. start there first. or DME fuel relay. both cheap to address.

[Goth]

The 3.2 has a micro switch toward the back side of the throttle body. It should just click when the throttle is closed, and just click right as the throttle is cracked open. When this switch stays on past idle, you get the symptoms you described.

[stlrj]

I suggest doing a basic tune up/mixture adjustment first and if that takes care of it...you're done!

[ZOA NOM]

Originally posted by stlrj
I suggest doing a basic tune up/mixture adjustment first and if that takes care of it...you're done!

+1


bad mixture can cause you to spend tons on a shotgun effort.

[450knotOffice]

I wholeheartedly agree with stlrj. I had these same exact issues you describe and at times the car would be absolutely underivable. I checked ALL of my intake fasteners for tightness and found all of them to be tight except for the clamps that attach the AFM to the big rubber elbow that leads to the throttle body (I tightened the clamps). I also removed the Idle Control Valve and cleaned it. It was fine. Still no improvement. Finally, I brought my car to my Porsche mechanic and asked them to check and adjust the mixture and idle speed. They had to use a Gas Analyzer in order to properly set the idle mixture and then adjusted the idle speed properly. Later that day when I picked up the car from them the car ran perfectly They said the mixture and idle speed adjustments were both way off when they got it. They adjusted both parameters to spec and the car has run perfectly ever since, and I mean perfectly.

More than likely your idle mixture and speed settings are off. Have those adjusted properly and then if you still have a problem try checking other sensors.

[911 in SC]

I have the same symptoms, but only AFTER I did a tune up (thanks for your help Dan and KC!!). I'm curious if there is something I could have 'hit' or 'bumped' while I was there that I was unaware of. I did notice that the PO had used Bosch WR-5-DC+ spark plugs, while I went with the Bosch WR7DC Spark Plugs that Pelican recommended. Could this have an effect?

If you guys think I should post this in a new topic, I certainly will...

Thanks,
Mike

[jester911]

Make sure you check all three plugs/sensors on the left side of the engine. CHT and flywheel sensors both can cause some of these symptoms.

You may have just bumped them and unplugged one just enough.

[BGCarrera32]

Originally posted by 911 in SC
while I went with the Bosch WR7DC Spark Plugs that Pelican recommended. Could this have an effect?

In a word, no. The WR7DC is the standard copper plug. Shouldn't be an issue if gapped correctly.

For the guy with the poorly idling engine, start with the simple stuff first. Make sure your oil fill cap is tight...

[911 in SC]

Originally posted by BGCarrera32
In a word, no. The WR7DC is the standard copper plug. Shouldn't be an issue if gapped correctly.

I didn't think so, but am at a loss of why the PO had different plugs.

That's one 'variable' I can put to rest. Now to check all of the connections to the sensors and vacuum lines.

[pk 84 911]

Thanks to all who responded. I think I will go the tune up route and try and check the whole system by using a manual.

PK