_SBradley_

I wasn't quite sure what to title this thread, as it deals with a whole host of things: rough and incorrect idle; hesitation and rough acceleration; EAC and EGR cleaning; and cleaning the IM using carb cleaner.

First, let me tell you my current symptoms, then I'll explain the history behind this post.

When I first start the car with a warm engine, the car idles at 1,000 r.p.m. for a few moments before gently dropping to the normal 750 r.p.m. Perfect!

However, as soon as I've driven anywhere, even just down to the end of my road (and possibly if I just revved the car while stationary, although I haven't tried that), the lowest the car will idle is 950 r.p.m. Even turning off all electrical systems, releasing the clutch, and waiting for one full minute, the idle never drops below 950 r.p.m. Also, although the idle fluctuates very little, if at all, I can hear periodic (every 2-3 seconds) changes in the engine tone, as if some valve is opening and closing slightly.

If I switch the car off and restart it, the idle drops immediately to 750 r.p.m., as described above.

So, how did I come to this point? Well, over the past six months, I noticed a gradual increase in two phenomena:

1. Hesitation or rough acceleration when accelerating using low to medium throttle at low to medium revs;
2. Surging or fluctuating idle when coming to rest after a period of driving.

So, I took the following measures:

• Sprayed a bunch of carb cleaner in short burts into the TB with the engine held around 3,000 r.p.m.;
• Cleaned out the EGR (man, that thing was dirty!);
• Cleaned the ports on the EAC;
• Reset the ECM.

Now, it could be my imagination, but I'm pretty sure the car now accelerates quite a lot smoother than it did before! This is a good start: one of my complains appears to be fixed! (I'll give it a few more days before I let myself be 100% convinced of this, but it's looking positive to far.)

Also, the car seems to start a lot smoother, and with fewer turns, than it did before. (Interestingly, my H22A does not have a starting air valve/air boost valve.)

The remaining problem is the one I described near the beginning of this post. These are the things I am thinking of trying to fix this:

• Check for air in the cooling system. I think I just undo the bleed bolt on the top of the thermostat and wait for a solid stream of coolant? Do I do this with the engine off or running?
• Compression check. Something I've never done before; but it would be interesting if I can find a reasonably priced tester.

I know there are many things that can cause weird idle problems like this, but I thought this case was specific enough that there might be something specific I should check for before I do anything else.

Any other ideas would be most gratefully appreciated. Thanks!

__________________
1994 JDM Prelude Si VTEC w/ 4WS
Sherwood Green Pearl (G-78P)

marcucci

This generally is all a result of any or combination of the following:

- vacuum leak
- dirty injectors (running rich)
- bad FPR (running rich)
- carbon buildup (dirty idle controls)
- maladjusted throttle cable (too tight)


I am adamantly against spraying any type of cleaner into a running engine. It's a good way to foul plugs, O2's, and cats. Not to mention it can be dangerous.

The EGR usually will cause a low idle by sticking partially open. When you clean it, it's a good idea to replace the gasket. It is best done with the manifold off the car as it is difficult to clean it, especially without just moving carbon buildup back down into the manifold that's going to just blow right back up into the valve again.

Don't bother with the bleed bolt, it's probably the worst way of checking for air. With the engine off and cold pop the rad cap and check the rad- make sure it is full. Check the overflow tank and make sure it is full. If that's the case you should not have any air in the system unless you recently bled it or have a head gasket leak. The compression test will tell you if that's the case.

Compression testers in the US are typically <US$40 for a cheap (but functional) one.

Check the other items I listed. Checking the comrpession is a good idea as well. I would not rule out vacuum issues based on the age of your vehicle. You might want to go over all of those hoses very carefully.

_SBradley_

That could be, although all the hoses I looked at this evening seemed intact.

Is that likely?

I think I've cleaned everything I can think of to do with idle controls. Well, not the fast idle thermo valve; but the revs drop just fine, so long as you don't drive anywhere, so that must be fully closing, right?

The throttle plate is definitely fully closed when the engine is idling high.

Heh. Oh well, too late now. I just did what it said on the can, which also stated "Will not damage oxygen sensors". Oh, I also used some on the PCV valve, which was explicitly described on the can. And I'm sure it made the car drive smoother: I went for a drive in between spraying this and cleaning the EAC and EGR valves.

Low but not fluctuating? That's sort of the opposite of what I'm experiencing.

Fair enough. I'll check that tomorrow.

I'll pop into Halfords on my way home from work tomorrow and see what I can do.

The one other thought I had: If I lowered the idle while it was in its 'fast' state, would the ECM then compensate for the new setting at startup? (So I'd end up with 750 r.p.m. at all times?) Or do you think I would end up with a too-low initial idle?

Thanks for the advice!

__________________
1994 JDM Prelude Si VTEC w/ 4WS
Sherwood Green Pearl (G-78P)

_SBradley_

OK, so I inspected all of the "upper" (easy to reach) vacuum hoses, and all seemed just fine. (No leaks at 20-30 psi; I don't know what they're supposed to handle.)

I also checked the throttle cable, and I think Todd might have been right (as usual ): perhaps it was slightly tight. Maybe I nudged it whilst cleaning the EAC valve? Anyway, I think this might account for the changes described below.

So, now when I start the car, it idles just fine at 750 r.p.m., as before. However, if I'm driving and I put the car in neutral and coast (not that it's something I do in normal driving; but for the sake of experimentation), the revs never fall past 1,000 r.p.m. Well, actually, they usually seem to drop to 750, then bounce back up to 1,000. Once I stop completely, however, they do (after a couple of seconds of being stationary) fall to 750.

Is this normal/expected behaviour? I never noticed it before cleaning the engine. Is there a reason why the engine revs don't fall to the normal idle position until the car has come to a stop?

I'm not too unhappy, though: the car definitely seems much smoother than it was before! Even from cold this morning, there was none of the stuttering/hesisation that I've come to expect over the past 6 months.

Thanks.

__________________
1994 JDM Prelude Si VTEC w/ 4WS
Sherwood Green Pearl (G-78P)

marcucci

Not very. The injectors do get nasty but that generally just leads to hard starting. The FPR can get flaky but that's one of the last items I would check (if there are no other symptoms).

Not necessarily. Honestly, I would remove it and plate it off or install a solid gasket. It's unnecessary unless you have many sub-zero winters and the car stays outside. You can easily check it by removing it and putting a piece of cereal box between it and the TB as a solid gasket.

Riiiiiiiiiiiiiiiggght.

Everything should be fine, it just generally does not do as good a job as disassembly and could cause an unwanted side effect like, say, a fire if you aren't very careful.

If you adjusted the idle via the screw while the ECU was advancing the idle to compensate for cold (warm-up) or the A/C, yes, this could be a problem. This is why you should never adjust the TB screw unless you follow all the conditions set out in the shop manual. If it is idling at 750, though, and idles high at 1000 RPMs sometimes, I doubt this is the cause.

Completely normal. I am not sure why but most manufacturers do this (on EFI cars) but almost all of them do it. My Isuzu idles at 1500 while coasting and then goes to normal under 5 mph. I am not certain if Honda describes this anywhere in the manual, but it is definitely supposed to do that.

The usual ignition suspects (plug, cap, rotor, wires) are usually to blame for mild hesitation and stumbling if they haven't been changed in a while. I suspect that's not your case, though.

_SBradley_

Oh, really? In that case, everything is probably fine. Once I stop, the car idles right on 750 r.p.m., and it sounds really nice and smooth.

I also think the car is quieter at idle than it was before. Quieter at idle, but louder when you open up the throttle. And definitely smoother.

No, they are all relatively new.

Thanks, Todd!

__________________
1994 JDM Prelude Si VTEC w/ 4WS
Sherwood Green Pearl (G-78P)

92-h23a1

I'm currently having a similar problem , although its at 750 when i come to neutral at a stop instead of staying at 750 it will sometimes drop down low a couple of times and most likely stall out. How would I go about finding what this is?

__________________
H-Series

_SBradley_

Well, it sounds as though it could be a more severe case of what I was experiencing before I did all the cleaning and spraying described above.

When I stopped, particularly after a longer drive, the revs would drop past the expected 750 r.p.m. to about 500, then bounce back up again; and that would repeat for about 5-10 times (or until I switched the car off).

Despite Todd's reservations about the dangers of spraying stuff into a running engine, I am definitely happier with my car now than I was this time last week. Whether or not you decide to try the same is up to you.

__________________
1994 JDM Prelude Si VTEC w/ 4WS
Sherwood Green Pearl (G-78P)

h8trix

This soooooooooo needs to be FAQed