Jimi Hondrix

1997 Honda Civic EX Coupe, Stock D16Y8 1.6L Vtec Engine, Automatic Transmission. Current odometer is 160K miles, Multiple owners, No service records or history when purchased in December 2014. 143K miles at purchase.

Intermittent low, lumpy idle only during times when transmission is in gear and brakes engaged (i.e. stoplights) and no electrical load present. Say what?, Yes, during times of intermittent low, lumpy idle (ILL idle henceforth) if I turn the headlights on the ILL idle immediately goes away and will not return. As long as the headlights or a/c compressor or high blower fan speed: significant electrical load is present the ILL idle is not noticeable.
During any other scenario of operation the idle is fine and as I stated the issue is intermittent but, getting increasingly more repetitive.

During times (stoplights) of ILL idle, idle drop down to about 400 rpm's. Turn on headlights or a/c compressor and idle raises to 700 to 750 rpm's (normal spec). In park or neutral with load idle is 700- 750 rpm's (normal spec) . There is presently nor has been since ownership NO: idle hunting, fluctuating or high idle issues. I recently cleaned the TB, IACV, vacuum gauge tested (all good reading), compression tested dry and wet (all good reading) readings. Blew cigar smoke through brake booster vacuum line + sealed off TB intake: no signs of vacuum leaks.

I plan to check:
All chassis and motor grounds
Spark quality and inspect rotor and cap.
Power balance test
Intake manifold leak check with TB cleaner spray
Block test to help rule out a head gasket leak . No loss of coolant in radiator or other signs of HG leak currently.

All suggestion, comments are welcomed and thanks in advance

Former User

Clean the IACV.

Txdragon

Good start there.
When you turn on accessories like AC, the demand forces the engine to compensate by idling higher, thus correcting your issue.

Jimi Hondrix

Thanks Ron. I forgot to mention that last week in attempt to fix the ILL idle I removed and cleaned the TB and IACV. Beforehand, I check ignition timing which, was spot on and did a vacuum gauge test: also checked out good.
Brought car to Autozone and they tested battery and alternator: battery's cranking amps and volts were in spec. Alternator outputting 14.2v

I suspect that if I can solve it, it will most likely turn out to be either a grounding issue, coil and/or igniter issue, or a random misfire in one of the cylinders. Just got to find enough time to diagnose. In the meantime I use the headlights during the day and the idle issue doesn't happen.

Former User

Did you also use the service manual procedure to adjust the idle speed?

Any CEL codes?

Jimi Hondrix

No CEL's. I was going to rule as much as as possible before attempting an idle screw adjustment. I do have the FSM on my laptop but, would you happen to have a quick reference you could share?

Former User

To do the procedure correctly, you must hook up an external tachometer or a code reader that reads live data to accurately monitor engine rpms.

Nave43

Have you burped your coolant?
Have you reset your ecu and let it relearn its idle?
Have you cleaned the FITV if you have one?

My big 3 wiring upgrade helped smooth my idle, most likely not your problem but cant hurt.

Jimi Hondrix

Thanks Ron. As far as purchasing an external tach are they the same as dash mounted ones? Do you know if Autozone rents tachometers through their tools loan program?

Jimi Hondrix

Yes

Yes

D16Y8 doesn't have a FITV

civic402lx

Get one of those obd2 scanner. like scanguage II or ultragauge. You can read any data, well majority of it, from the gauge.

Jimi Hondrix

Those are cool but, a bit pricey. I could see it getting a lot of use though if I purchase one.