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Discussion Starter #1
My 89 420SEL has had a vibration ever since I purchased the car in August. The car has 102K miles and is immaculate. The vibration is coming from the rear and everything looked physically great. So I decided to install new flex discs, sub frame mounts & rear diff mount.

The mounts & discs were not cracked but the rubber did seem a little hard so I am hoping the car will ride smooth after this work.

I also had a weird hesitation problem that I concluded was from the EHA, so I did the 1/4turn CCW on the adjustment screw as suggested by threads on this site. The adjustment did help but I want to measure my lower chamber pressure and adjust my mixture.
 

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560SEC, 190E, Frontier, 240Z
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1/4 turn CCW on the hidden EHA screw? That would tend to lean out the mixture off-idle.

I've concluded the following after F-ing with every adjustment and now having a really great running CIS.

Set warm engine idle Lambda to 50% ish.
Then increase RPM to 2500 and the Lambda should go DOWN to 30% ish.

If it does not go down in percentages then you might try to tweak the hidden EHA screw CW to enrich off-idle mix and get the aforementioned result.

Going down in percent at higher rpm indicates the system is going a little too rich off-idle, but the CIS is still able to compensate. When you go WOT and the system goes to "combat" power you will be plenty fat. In my car this means 14.7 AFR putzing around and 12.5 flat out.

The very slightest little fuel leak from EHA will screw up the operation at high power.

Further you need to bleed the FD after removing and reinstalling the EHA by way of the pressure port. If you don't it can cause problems and no-starts sometimes several days later in my experience.

I've had a blast messing with the little EHA.
 

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Discussion Starter #3
after reading your response I realized that I said I turned the adjusting screw CCW when in fact I turned it CW to richen the mixture. Aside from the random hesitation I also had a stumble when I stepped on the accelerator quickly from a stop. I will try to set the mixture s you say so that it will be fat at WOT
 
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