possible idle problem test?

[b3nsonx]

background info:
car is 91 cb7 with f22a1 at 208k miles
fast idle thermal valve is new
checked for vacuum leaks several times with carb cleaner
i have a broken rear motor mount
car is automatic
idle screw has been checked.
throttle cable has been checked
mods are I/H/E

problem:
sometimes my car sometimes idles a little too low and engine starts to shake a bit
sometimes my car's idle surges up and down between 800-1300 rpm while stopped in D.
and most of the time my car just idles high at around 1200 rpm and occasionally drops down once in a while
also when im going like 20+, then i let off the gas pedal the rpms sometimes dont drop down and they stay at around 1500 rpm, until i press on the brake pedal, then it forces the rpms to drop and then it will stay at around 1200 (most of the time this happens).

test:
my mechanic told me to unplug the VALVE ASSY., ELECTRONIC AIR CONTROL.
he said that if it stops surging and the high idle goes away then the problem should be caused by this unit.

results:
so far i noticed that my idle has never gone above 900 rpm, it might be idling a little low because the engine shakes, or its just my broken motor mount that is causing the shaking. it has been pretty consistent so far.
only problem i noticed driving with this unit unplugged is that when i let off the gas, my rpms drop alot faster than usual, and this causes some hesitation in the car.

so what do you guys think? should i change my electronic air control valve?

[buckysaccord93]

hahaha i just fixed this problem.. all it was for me was one spark plug was shot.. check your spark plugs

[b3nsonx]

yea my car is due for a tune-up soon, so we'll see

[buckysaccord93]

yeh i was driving my auto with it doing that for like two weeks and i was looking for vacuum leaks the whole time.. when my one friend said check the spark plugs and by god.. that was the problem lol..

good luck hope all it is, is your spark plugs needed replaced

[b3nsonx]

how old were your sparkplugs though? mine are only about a year old with like 10,000 miles on them
and what brand did you use?

[buckysaccord93]

ngk's and they were around the same as yours maybe 1k or so more miles on them but about same.. if you wanna check just walk down with a 5/8 spark plug socket and take a gander at them all only takes like 5 mins and you dont even get dirty lol

[b3nsonx]

alright thanks for the tip on the sparkplugs

[chronicponic]

I got new plugs, wires, cap, rotor.. Mine still does almost the exact thing as his. Except mines a 5sp..

[HondaFan81]

Copper spark plug change intervals should be around the 20,000 mile mark and can actually last longer. I change every 20K miles to maintain peak performance, gas mileage. Changing earlier is a waste of money.

The purpose of your IACV/EACV (intake air control valve/elect. air control valve) is to maintain a proper idle (i.e. 700-800 RPMs) under all conditions. Unplugging this device obviously prevents it from working and opening, therefore lowers your idle. However, this device has the capacity to increase your idle RPMs 200-300 RPM to compensate for engine load (i.e. defrost, A/C, P/S, etc). Therefore, the reason for your idle bog/hesitation is exactly because it is unplugged, it can no longer compensate to maintain proper idle.

Technically, when you uplug your IACV, your idle should fall to a consistent 500-600 RPM. If engine stalls, then your idle is not set properly. If engine maintains higher than 500-600 idle, it is not set properly or has vacuum leak.

I have a couple suggestion:

1) If your automatic tranny rear engine mount is shot, trace the vacuum line going from your intake manifold to this mount. Plug the intake manifold PORT going to the line (this eliminates the vacuum hose & mount potential leak). If your idle improves, then you either the mount or vacuum line to this mount is bad.

2) If idea # 1 yields no results, then proceed to setting your base idle properly. Refer to Haynes or Helms inspection manual. If you still don't understand, PM me and I can walk you through it.