'92 Civic DX Hatchback Idle dropout problem
 

I just had some major work done on my '92 Civic DX Hatchback
(automatic transmission, A/C, NOT a VTEC, the regular engine) at my
local Honda dealership. Car had been running well. Have ~85,000 miles
(I'd don't drive much). Now I have a very frustrating idle problem
(the engine randomly almost dies) that no one can figure out. Here's
the story:

1. In May, the engine began sputtering occasionally at stoplights,
especially when trying to accelerate from a stop. Led to a few close
calls with oncoming traffic, as the engine almost died mid-
intersection.
2. After this happened ~3 times over ~3 days, the engine just died,
wouldn't restart (cranked OK), & had to be towed to Honda dealer.
3. Codes revealed a faulty Idle Air Control Valve (IACV), which was
stuck shut. IACV was therefore replaced.
4. Also had other major maintenance performed (it was time anyway):
90,000 mile service, including Valve Clearance Adjustment, timing
belt, water pump, new plugs & air filter.

Now the trouble really began...

5. Car didn't perform well at highway speeds (hard to quantify, but
engine just seemed louder & less powerful at high speeds, ~80 mph).
ALSO, at idle, in gear, at a stop, idled roughly, and it seems like
the motor is cutting off for a split second. Almost dies, then
recovers. Seems to happen more when it is warmer out (~75-80 oF).
Rarely happens if either the car is in Park/Neutral, or if the A/C is
on, or if you're actually moving.
6. First the dealer's mechanics couldn't observe the idle problem,
then didn't believe it was an issue, then asked if I was sure it
wasn't happening before I brought the car in the first time, etc. They
also said that the IACV had an "adjusting screw" that was improperly
adjusted, and that it was now adj. properly. (Next time, I was told
that the IACV does not have any adj. screw!!) Did NOT fix the idle
problem.
7. Back again to dealer. Service manager is trying his best, and
replaced the PCV valve and its hose. No change in idle problem.
8. Back again. Manager discovered that the valve clearance had been
adj. too loose, and timing was 5 degrees retarded. Fixed the
clearance, rechecked timing, idle speed, etc. Also cleaned out the
throttle body (they said it had some carbon buildup). All this now
seemed at last to improve the high speed driveability somewhat.
Possible improvement in the idle problem (seems less frequent), but
still not gone.
9. Now, the idle dropout happens like this:
a. Car is idling, and fan comes on. This kicks up the idle speed a
bit.
b. Fan shuts off. After ~7 seconds, idle speed drops back down.
c. After ~20-25 seconds more, engine drops out...idle speed for that
split second makes like it is trying to go to zero.
d. Cycle of a, b, c repeats (for as long as you're willing to sit
and wait).

The specific timing of the problem described #9 makes me think it is
unlikely to be plugs, SP wires, rotor, cap, etc. (Wires & cap were
replaced ~2 yrs ago (non-Honda).) Coolant-temperature related? Some
other kind of sensor? What else could it be? A faulty, new IACV? Other
things I've seen mentioned: coolant temp. sensor; Throttle Position
Sensor, coil, igniter, SP-etc..

Sorry to be so long-winded, but figured I'd give you experts all the
info I have.

Desperate for help!! Thanks!!!