TomCat39

Hi all,

I've seen all kinds of idle things for out cars, the two most usual suspects are the IACV (all years 92-00) and the FITV (92-95).

However, every so often I seen other things suggested such as Coolant Temperature Sensor.

This got me to thinking, I don't even remotely know what all can affect idle on our Hondas.

I'd like to create a list of everything that can affect the idle of the car. Including to the uncommon ones and I'll make sure they go last on the list.

So here are the ones mentioned in this thread:

1)IACV - Idle Air Control Valve
2)Intake, Intake Manifold and Vacuum Leaks
3)Maladjusted Idle Screw
4)FITV (92-95 only) - Fast Idle Thermo Valve (I think the IACV will compensate some when this first starts acting up)
5)ECT - Engine Coolant Temperature sensor
6)TPS - Throttle Position Sensor
7)PCV Valve (92-95 typically) - Positive Crankcase Ventilation valve
8)Ignition/Mechanical Timing errors.

What else can cause idle problems with our 92-00 civics/del sols?

Oh, and I did look in the FAQ and for idle it only talks about the Set Idle Procedure, the IACV and the FITV. It doesn't even mention the ECT or anything else that maybe brought to light in this thread.

Former User

92-00 Civics:
IACV
Vacuum and intake air leaks
Misadjusted idle screw
ECT sensor
TPS

For 92-95 Civics, also add:
FITV
PCV valve

TomCat39

PCV Valve won't affect idle on 96-00?

tony_2018

idle problems? charging system, ac system?

Former User

Typically not, because the OBD2 ECU is better at maintaining the proper idle speed with slight fluctuations (increased or decreased) of air intake.

TomCat39

Sounds good, can the Intake Air Temperature Sensor (IAT) affect idle?

And what about the Manifold Absolute Pressure (MAP) sensor?

Former User

Generally not.

Yes, but only indirectly by affecting engine performance. When you have MAP sensor problems, idle issues are generally the least of your problems.

Former User

Agreed, but again indirectly through general engine performance and not specific to idle system.

True, but for an idle specific issue, it's an ECU (no idle up) rather than A/C problem.

When the A/C system itself causes idle problems, it's due to increased engine load (over-pressurized system or locked compressor).

Former User

The ECT sensor is critical for idle speed. Can you venture a guess?

TomCat39

Thinking about it, I know it would affect fuel trim as it runs richer when cold as if the motor were choked.

As for idle, I'm drawing a loss at the connection.

Former User

When the engine is cold, the engine idle speed is high. This happens because the ECU sees the low coolant temp from the ECT sensor. The ECU responds by telling the IACV to bypass more air to the IM, resulting in a higher idle speed. The idea behind the high idle speed when cold is to shorten the time for the engine to reach full operating temp, which is best for performance and fuel economy.

So now you can see why a goofed up ECT sensor or circuit can cause a goofed up idle.

NotARaCist

iTrader: (1)

Slightly incorrectly set timing can also cause idle problems, from what I've seen.

TomCat39

Mechanical or Ignition?

I'm assuming ignition as I think a tooth off in mechanical would pose more than just and idle problem.

NotARaCist

iTrader: (1)

Both. If you use the wrong combination of belt/cam gear/crank gear on certain mini me setups, or even if a stock engine has had the head shaved too much, you can end up a quarter or half tooth off, which (under the right circumstances) can give a fucked up idle.

TomCat39

Good stuff, thanks.