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I drove my 86 that is my better helf's daily for the first time in a month or more the other day and noticed just how bad it idles when hot(still), possibly more since the weather is warmer.
It isn't the wiring, the engine harness has been replaced, I've grabbed and shook it all over, checked and cleaned all the harness plugs.
It isn't the ignition base timing, I've had it on the high and low side of spec, the balancer has not slipped the ring either.
It isn't secondary ignition, everything from the HAL sensor to the plugs are new, NGK Bosch and Bougicord.
It isn't fuel pressure, in tank is new VDO, sock filter new, main filter new, external pump is shiny blue and quiet and it has good power and starts up fine.
It isn't a vacuum leak, I've replaced all the hoses and the flame trap, and the intake pipe, and the AMM(reman), and the one over to the ignition box even. I've SOAKED the (cold) motor in spray can either, all over, under intake, all of it, nada change in idle speed.
The throttle valve and idle speed are both set per the book.
The AMM is adjusted with my home made LED.
It isn't running hot.
The ECU temp sender is new and well grounded.
All the grounds check out good, both on the motor and at the ECU.
The idle control valve is clean and works well.
The O2 sensor is new, unplugging it has no effect on the idle miss.
It get's reasonable MPG, and has reasonable power for a 240+K B230F, does not smoke, and uses no appreciable oil between 3K changes. It does have some piston slap but I've had a lot worse in these motors.
The only thing I haven't done is swap the ignition box and ECU out.
It seems to be worse when real hot, heat soaked hot, like a quick stop after a highway drive, or sitting at a drive-through. It never chokes off, or even get's close, thanks to the idle control motor kicking the RPM up if it misses badly enough to lower the RPM to where it thinks it needs to intervene.
It missed badly enough a couple times that the idle control did in fact raise the RPM's up a bit to try and compensate the other day. I have in the past disabled the idle control, such as when you set the idle speed manually, and it still misses.
I really don't think it's ignition, and it isn't a regular miss. The only other symptom is a slight hesitation off idle, that I think is worse when cold.
Other than swapping the ECU/Ignition box, the only other damn thing not new underhood are the injectors, and the thing runs perfectly smooth on the road, and holding some steady RPM above idle with no load it varies some, but so do all the redblocks running LH injection I've had, hundred RPM or so at the most.
What am I missing here? I never ran a compression test since I saw no need to, the motor is old but performing well and no smoke/oil usage usally = healthy internals with these. It has done this from the first day I turned the key, through my removing the motor and trans to re-seal them, my extensive tune-up and re-hab, and after maybe 6K miles now of daily use since then it still does it, worse even with the summer heat I think. Thoughts?
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