Detroit DDEC II erratic idle - Diesel Truck Forum -
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post #1 of 1 (permalink) Old 06-07-2017, 06:48 PM Thread Starter
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Detroit DDEC II erratic idle

i freakin hate electrical gremlins.

so, this trouble is in my new bus; a '91 Setra (details in sig).
i do have a "high idle" button, which works fine.
throttle works fine.

the trouble comes when it's just idling. it wants to kick up to 1000, ...1500, ...even 2000rpm.
i'm quite certain it's electrical because it just surges up to an rpm, then without notice it'll drop right back to 600rpm idle. it'll even VROOOM, like there's a ghost in the driver's seat. sometimes just a burp.

sometimes it rolls up, fast or slow, and sometimes it jumps.

NO, it will not "kick down" with a throttle bump.

engaging the high idle does nothing to remedy. the higher of the two "inputs" wins.

?? a couple of times, i loaded the engine by turning the steering wheel, and it immediately dropped to idle. ??
but that's not a consistent remedy.

when it's in gear (auto), it seems to behave, for now.

it's "fly by wire" with a Williams pedal and a DDEC II engine ecu.
i've ordered a new DDEC II harness because mine is original and has seen enough heat to melt the protective sleeving.
i've also ordered a new potentiometer harness for the Williams foot pedal.

anyone seen such a thing?
- i believe the tranny is consulted, but that shouldn't affect actual throttling.
- ecu could be to blame.
- 40' of harness extension could have issues.

thanks, all

'96 Chevy k3500 CC, 6.5L DD, Auto
'83 IH S1800 CC, dt466, 10spd
'76 GMC P8M4905 Buffalo Bus, 8v71 DD, 4spd
'91 Setra S215HDH Bus, DD 8v92TA DDECII, Allison HTB748 Auto, Voith Retarder
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