Below,in quotes, is my last post which shows all the things I have tried so far to fix a severe bucking problem between 1,500 and 4,000 RPMs (for background).

I checked the timing and it shows to be off about 90 degrees at idle. However, the idle speed is steady at 750, and it does not buck in neutral or park --- only under load. Can the timing be off that much and only have a problem under load between 1,500 and 4,00 rpm?




"I continue with my quest to diagnose a severe hesitation at load on a 1995 940 Turbo. If I try to accelerate with any but a light feathering of the gas pedal you get it. Also when cruising at a steady speed on the highway and you go up any kind of an incline, you get a slight rythmic hesitation.

I have posted this problem several times and have tried all suggestions, (see below).

HOWEVER, I NOW HAVE SOME NEW EVIDENCE THAT MIGHT MEAN SOMETHING. I DISCOVERED THAT THE HESITATION GOES AWAY AT ABOUT 4,000+ RPMs. So what does that mean in my search?

I have (by category):

Fuel Delivery:
replaced fuel filter.
filled tank with gas.
put in bottle of techron.
resoldered FI relay.
swapped fuel pump relay.
swapped fuel pressure regulator.
checked fuel pressure at rail (38 at idle, goes up with RPMs, and goes back to 38 when bucking).

Electronic/Electrics:
swapped AMM.
swapped coil.
replaced distributor cap and rotor.
replaced plug wires.
replaced plugs.
swapped power stage.
swapped RPM sensor.
Cleaned grounds in trunk, pass, and driver. footwells, and at fuel rail.
disconnected O2 sensor.

Air/Vacuum:
inspected all and replaced some vacuum hoses.
inspected turbo hoses (replaced one, swapped one).
pressurized system at turbo inlet (after hearing air under intake manifold, but not finding a hose problem, I replaced intake manifold gasket).
replaced two idle motor hoses.
cleaned throttle body, with new gasket.
Swapped IAC.
Plugged intake to EGR pipe.

Also:
Checked exhaust for individual bursts (to see if blocked).
There is no black smoke from the exhaust when the hesitation happens.
There are no codes (only 1-1-1).
I then tried to replicate the problem on my 1994 940. I disconnected several air hoses off the intake manifold to create air leaks. It did not produce the same effect.
It stopped doing it at the end of a 200 miles trip and returned a day or two later. "