RPM goes extremely high when in Neutral?

When running, no problem. When in neutral (class released), RPM goes
tremendously high. I usually have to turn off the ignition and turn back
on to move on about a feet in STOP signs.

It only happens in Summer and when the engine is already hot (Engine
Temperature is normal though).

Please tell me what shall I fix.

 

---------------------


This is not a 'psychic automotive diagnostic service'. Look in the
Yellow Pages for that.

All we know is that it has a key, and that it overheats. It could be a
Honda motorcycle. . . . . Help us out a bit.

'Curly'

 

Sorry that I didn't make that clear. Mine is 89 Honda Civic (Wagovan).
Recently it's been doing that (High RPM when engine is hot). I thought
radiator flush was the problem as I never done that in the past. Flushed
last week and didn't solve the problem.

Also my car is 5-speed manual (1.5 liter and currently about 150000 miles
on it).

Could you please help.

 

How high is the RPM revving?

Did you purge the coolant system of air?

I find it takes at least a half hour of the car sitting at idle before the
fan comes on twice, during the purge process.

If air is in the cooling system, then certain engine control components are
not necessarily being cooled adequately, and erratic revving will occur.
Very common problem which is easily fixed.

 

Well, RPM goes like 5000 in only 4/5 seconds. I never let it go higher.

I didn't purge the air intake. Do you think that may solve the problem?

 

My 1991 Civic LX manual transmission (might be the same engine as yours) was
revving up to only 1200 or so, then falling, then revving again, last summer
when sitting at a stoplight and whence, back home, I found air in the EAC
valve. A proper purge fixed this. Would more air in the system cause revs to
5000? Dunno. But if you didn't properly purge the air, then that's the first
thing I would do here.

On the matter "purge the air intake"(?): I think we're not quite on the same
page here.

What I mean is as follows:
After draining and re-filling your radiator cooling system recently, with
the car of course fully cooled, did you then (1) leave the radiator cap
off; (2) start the car; (3) wait until the radiator FAN came on twice; (4)
added more coolant to keep the radiator neck topped off throughout?

As I mentioned, it takes a long time (30 to 55 minutes) for the car to warm
up enough to make the fan come on.

 

Well, RPM goes like 5000 in only 4/5 seconds. I never let it go higher.

I didn't purge the air intake. Do you think that may solve the problem?

 

Please turn quoting back on in your newsreader.

You have an odd problem indeed. This phenomenon could /only/ occur if an
adequate amount of fuel and air were being admitted to the intake, that
amount increasing with the revs, so as to sustain the increase.

I almost think you have a dirty throttle body that is so filthy it's
causing the throttle plate to stick open.

Low coolant results in surging (like with a big air leak), not a steadily
increasing idle that occurs over 4 or 5 seconds.

Questions (please intersperse your answers):

You say it's "recently" been doing this. When is "recently"?

Had the vehicle been subject to heavy rains or driven through deep water?
Had a collision?

What happened to/with the car immediately before it started to rev like
this?

If you were to let it rev, will it eventually reach redline? You have a rev
limiter, so it ought to go no further than abut 6,800 rpm.

 

Also, what kind of maintenance has the car had? When were the
cap/plugs/wires and rotor replaced last?

Does the car seem to have poor power all the time, and to start slowly with
lots of cranking?

 

ITEM #1. _check the throttle cable._ it's probably sticking open. the
engine /cannot/ rev is it's not getting air & gas.

if that's not it, i concur about leaving it on - the rev limiter will
protect it, so see if it corrects with the eacv. also look for vacuum
leaks.

 

I agree, I had a cruise control cable stick on my 85 nissan that caused this
problem, made the throttle stick way too far open.

 

What is "purging the air intake"?

 

=============================

That's a mistake . .

I'm sure they meant to say 'purge the air from the cooling system' Honda
povided a bleed nipple on several models because a big bubble of air can
get trapped, which fools your temp sensors (because they don't work
correctly unless they are submerged) and your computer can do strange
things with your timing / F/A ratio, etc.

'Curly'

 

You forgot some steps. (5) Turn the heater dial to max HOT
(6) Release air from the bleed nipple. (7) Close the nipple.