Hi Theo,
I finally got around to replacing my air box mounts, and now everything fits properly. The vacuum lines behind the box are now  connected, so shifting is once again very smooth.

Now I have an odd problem, possibly it existed before, but now it is very pronounced. When opening the throttle hard (3/4 or more) from a dead stop, the car bogs down, vibrates and stutters until it's over 2000-3000rpm. Once I'm over 3000rpm, power is good.

Everything ignition related (wires, plugs, coils) are all less than a year new. The only items that are older are the distributor caps and ignition rotors. Have you seen these items cause this kind of problem.

I am also thinking of fuel delivery as well, and will change the fuel filter along with having the injectors flushed.


Hi Paul,
If you expect trouble in ignition, Check the car in the (real) dark for sparks or arches and remove a few plugs to check for fouling. Maybe spray a bit of water mist to simulate moisture.


Hi Theo,

My spare set of EZK and LH computers showed the same issues as the ones currently in the car. As for grounds, how do I go about checking
that? I did replace the battery ground strap a few years ago, but that is all.

Unfortunately I don't have an auto scope, but I am sure my mechanic does. I think I noticed this issue starting (to a lesser degree)  after I had the plug wires replaced by my mechanic.  Is there a webpage that lists how the wires should be connected, on  the distributor cap. I want to verify that they were installed correctly.



This is what the sequence should be:
1. Distributor cap cyl. l-7-6-4
2. Distributor cap cyi. 2-5-8-3
divided into 2 separate ignition circuits.
Firing order:1-3-7-2-6-5-4-8

Coil (Q/V):
Primary resistance
Terminals 1 + 15: 0.4 - 0.7 Ohm
Secondary resistance
Terminals 1 + 4: 5 - 8.7 kOhm
Voltage at
terminal 15 with
engine running >l0V
High-tension distributor (a):
Distributor rotor Suppression resistor 1 kOhm Inspect for damage, tracking or oxidation.
Spark plug caps (0) Suppression resistor 3 kOhm Inspect for damage, tracking or oxidation.

No loose pins in the plugs? Checked them too with a meter? Correct resistors in the caps (or used original ones?
Grounds: ground points near the ignition coils, one strap at the passenger side cams, one big one at the bottom near the exhaust.

1992 928gts Midnight Blue
1988 928s4 Cherry Red (Sold in 2006)
The Netherlands


Hey Theo,
It turned out to be the distributor caps and rotors that were a large reason for my hesitation and stuttering under full-throttle, as the car is much better after I replaced them. One thing I did notice that was odd was that the plug wires on the distributors had an ashy residue on the inside of the plug wires, and on the caps themselves.
One thing I noticed was there was no dielectric grease in the plug connectors - my mechanic had installed these wires just last spring. I made sure to clean all the plug wires, double-check everything, make sure ground straps were on tight, thoroughly and put on a generous amount of dielectric grease when I installed the new caps and rotors.

The car is back to feeling strong, but idle is still a little low and wobbles ever so slightly. I guess I still have a vacuum leak somewhere. Ah well, it's always something I guess.