idle up down up down

[MarkgM]

I have an '87 Accord LX - carbed, auto trans.

Got it tuned up (as may be seen in another thread farther below) - all old issues are gone.

After the tune-up, the idle (in drive, breaked, not moving) was rough enough to say the car had a shimmy. I called and asked about it, and it was suggested to try some gas cleaner, so I did, and 100 miles later, I have to say the idle is as smooth as it has ever been.

Seems like the carb must have a passageway that got cleaned out good. Another change that has taken place with this smooth idle is that it is higher, but I don't think it was losing RPMs earlier from the shimmy, I think it actually has idled up from ~800 to ~1000. So that's one thing.

The funny behavior is that when decelerating to a stop or real slow speed, the idle sometimes drops all the way to nearly nothing, it comes very close to stalling. And moreso when its not fully warmed up, just sitting at a stop sign the idle can give away like it's stalling, and then just before it does, kick back in again and rev itself up over 1000, and then lose it again, and then catch itself and rev back up again.

It's not a 100% thing, but it seems regular enough especially before the engine is fully warmed up. Any idea what I should do or be looking at to diagnose for this? I know the hot-air door diaphragm isn't working, but I skipped the $15 for it at the time, because I didn't think it was important. (I'm not in cold weather country.)

Thanks in advance.
- Mark

[k-roy]

Might be a vacuum problem. I had to replace the Idle air control valve on the front of the carb to fix that problem.

[MarkgM]

Oy! Went to the local Honda dealer today, and looked at what appeared to be the right part on their parts pic/list for this carb (78 LX, 2 bbl, auto).
Picpart #8: "diaphragm" Part No 16020-PG6-005 $67.03
And wasn;t sure if this was throttle control or what,
Picpart #18: "diaphragm" Part No 16045-PH4-661 $53.42

These are quite some expensive parts to play around with! Where did you go for the part?

[DanG86LX]

Junkyard,
$2 CAN

took the whole carb for $25CAN :lol

[MarkgM]

Rats. Went to 3 salvage yards today. 2 did not have the carb. The other wanted $50, naturally no guarantees, and I'm thinking about the garage where I could take it to have it fixed. They have a number of 3-g accords and maybe some old parts in their inventory already. Why should I drop $50 on a risk, only to have to start over again? I think this one is going to go into the shop. Probably to the tune of $100 to $150, I'm guessing.

Thanks, Kroy, for the advice on where to look.

[Poodlehead]

$50 bucks doesn't sound bad for the entire carb with all the crap hanging off of it. At least then you would have parts to swap...

I've got an 87 DX too and just change the accelerator pump yesterday with the carb on the car. Now the idle on it varies too like you are describing. I'm HOPING this might be due to the grease I used to hold the accel pump, o-rings and spring in place, but I've put about 30 minutes driving on it and still not perfect.

Also, the fast idle is not consistant (I shouldn't have screwed with it), but that may be more related to the temp difference in the morning and afternoon.

I hope putting more miles on it will help it smooth out. I can't think changing the accel pump would screw with the idle, but then again, I shouldn't have screwed with the fast idle screw in the back...

[MarkgM]

I'll have to keep that in mind. If all you mucked with was the accel pump, which is something I hadn't looked at. I don't see how that could have anything to do with the fluctuation in the idle.
But one idea - may be temperature related, ito the water temp. The car is going up for sale now. I know I had it in to the official mechanic, and the idle up/down is gone. He said there was a wire off on the choke mechanism - damn! I didn't see that. readjusted the idle speed, reset the timing.

[geofstan]

Hi MarkgM I had the exact same problem with my idle and all it was , was my PCV Valve.
Hope this works for you

[MarkgM]

Oh, thanks. There was a vacuum leak under a (newly replaced) PCV. That's an interesting piece of hose, and it was old and needed replacement.
The idle seems pretty consistent now.