midnightfirews6

iTrader: (1)

Been having weird issues with my '84. LG4, still with the e4me and digital spark advance. Auto>t56 swapped. It's been having an intermittent part throttle (~1/4 throttle in any gear) misfire that feels like spark, but i've gone through the whole ignition twice, dizzy to spark plugs. I've also replaced the carb twice with remanned units from national carburetor due to leaks. The intake manifold has also been cleaned and resealed last year due to a coolant leak. I'm at my wits end trying to chase this down. Otherwise, it starts fast and consistently and runs great above ~1/4 throttle. I'm not sure that the secondaries are even kicking in when it clears up and runs well. It has an intermittent cel for running rich. The other weird thing is that the revs hang above 35 mph. any gear, clutch in or out, cruise on or off, a/c on or off. They just sit around 2k +/-500 rpm, and the pedal gets sucked down like the cruise is set until i slow below exactly 35 mph. I haven't changed the ecm. Considering trying that or going m4me/ vac advance, but i'd like to hear other opinions before throwing parts at it.

Vader

Does the carb have a high idle solenoid? If so, is that adjusted properly? It can be unplugged or removed for diagnosis of the issue.

Another thought is that the something is allowing extra air, either from binding throttle plates, stick shafts, a leaking EGR possibly commanded ON by the ECM, an incorrect PCV valve, or some other source.

naf

iTrader: (7)

yes

The ECM will command the high idle solenoid above a certain speed in decel

what's the dwell doing at part-throttle? don't assume the mixture is rich at part throttle even with a 'rich' CEL code.

Dens71TA

iTrader: (5)

You say you haven't changed the ECM but did you swap the PROM to the LG4 manual version? The auto PROM uses the
Park/Neutral switch on the shifter to let the ECM know if the car is stationary or in drive mode for idle and drive programing.

Scott's 83' Z

Oem spark plugs or some other brand? My 83’ ran like crap when I tried other “ better” spark plugs. If you used something else I would go back to OE plugs. Having the same issue with my Ram truck as well.

Vader

Good call. However, from the binary files I've looked through, the park/neutral is usually defined as an adder to the base/target idle. Nonetheless, it could result in the overall idle or IAC steps being higher under conditions that wouldn't exist with a manual trans, depending upon how the conversion was done.