Swiss964

Sorry for the late reply
No I did not find the issue
In the meantime, I overhauled the alternator ( bearing, diodes, collectors...) got the distributor overhauled and tuned for centrifuge ignition advance (great address in France, La clinique centrale de l'allumeur, did an amazing job)
Changed oil to 20W60, put NGK iridium plugs
Nothing ....
I did discover a leak in my exhaust pipe just at the cat connection before the lambda sensor, I will disassemble and weld asap
When I disconnect the lamdba sensor, I still get the bucking, but this could be due to the fact that the DME works in safe mode. I will keep you posted

Richard Curtis

This is a long shot but ... how old is your battery? Is it putting out 13.8 volts or better at a steady 2,000 rpm? I've read and heard that a weak battery can contribute to strange running problems.

Swiss964

Battery is good, steady 13.8v on scantool with plotter, curve is flat throughout rpms
I am thinking that my exhaust leak may influence the lambda and put the car in degraded mode, Or Idle adaptation not working, I did it with the scantool, but I am not sure it is doing anything, I do not notice any effect, people have been talking about the hammer being in some case the only solution... but 1200$ for a hammer is an expensive trial an error to me

Swiss964

Another thought, I measured the vacuum at idle in the intake (gasoline vapor recycling port) get around 13inch Hg, this is very low as in theory should be above 17, this indicates as per manual either a wrong ignition advance or an intake leak
My distributor was overhauled and I tested the intake for leaks with fume
I am wondering if this value is normal for the flat 6
My ignition advance shows 4° on the scantool at idle but this varies with the chip i put in, with the original RUF chip I had 2° and with the steve wong one i have 4°, but with both 13inch /Hg of vacuum, I have seen that the standard at idle is below 1°
would anyone have experience with this?
Thanks

Michael D'Silva

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ahsan127

I had this same issue on a rebuilt engine with 15k miles. I did a valve adjustment along with new spark plugs and that got rid of the problem.

dlpalumbo

I experience a 'buck' as you describe when I lift my foot at low RPM. I don't get bucking when I have throttle applied at this RPM. Only a single 'buck' when I either just lift, or lightly apply.

I have attributed this to the idle switch being engaged too early or possibly bouncing in this intermediate state. I haven't dug into it to diagnose. As you've fiddled with everything else you might try this as well.

I suppose it could also be a worn spot in the AFM's resistor pad. This would be more troublesome.

Good luck,

Dan

ducnine

I just replaced my O2 sensor today. Drove the car early in the morning and then later on in the evening. No bucking concerns. Hopefully this did the trick. If so I am wondering why it took me so long to try this relatively inexpensive fix.

Real easy to do as well.

• Just lift the rear of the car and remove the Left rear tire.
• Then remove the heat shield on the Cat.
• Spray some PB Blaster or penterating fluid on the O2 Sensor
• Use an O2 Sensor removal tool (I borrowed one from the local auto parts store)
• I was able to unplug the O2 Sensor inside the engine room by squeezing my hand by the blower.(no removal of any parts necessary)
• Install new sensor
• Use soapy water on the grommet on the O2 Sensor to get it back in place (makes install of this grommet super easy)
• squeeze your hand back in behind the blower and plug the O2 sensor back in

Attached are some pictures of the old sensor in place and after removal and the new sensor in place.