Greetings.

I did try the link in the stickied thread, but apparently it has expired...so, apologies in advance for adding to the enormous pile of Accord idle issue threads.

Purchased a '99 Accord EX coupe, 4cyl, 5-spd. two years ago. My son drives it more than I do. about 160K miles.
AFAICT, the engine has had no major work on it by the PO.

At purchase, it started out throwing the VTEC code. Replaced the VTEC solenoid. We had intermittent issues with the VTEC after that (loose ground or electrical lead somewhere?) but that seems to have stopped since the first of the year.

Last summer & fall, developed this idle issue: while driving, and coming up to a stop, the ide would drop, run rough, and occasionally stall. Some days were worse than others; some days it wouldn't do it at all. It seemed worse when it got really cold; now weather doesn't seem to be a factor.

On cold start, it idles fine. Under most conditions (just sitting) at temp, it idles fine. Runs fine. Since repairing the VTEC, It is throwing *no* codes.

What's been done:
- removed cleaned VTEC solenoid.
- replaced VTEC solenoid
- removed & cleaned IACV
- replaced IACV
- checked & cleaned IACV & VTEC electrical connections
- removed top half of intake plenum & cleaned it. Wasn't bad. Some carbon, but not much.
- cleaned the distributor cap contacts & rotor. They were scaly & should be replaced. Plugs are cafe-creme, no issues at the moment & cleaning changed nothing. I intend to replace the cap, rotor, wires & plugs in the near future.
- checked for vacuum leaks (cannot find any after spraying every hose, fitting, flange, etc I could find with intake cleaner).

Yesterday. I tried the idle reset protocol...and here's where it gets weird:

- Pulling the IACV plug changed nothing.
The air bleed screw was difficult to find, because the PO or his mechanic filled in the recess with RTV. After scraping that out (which changed nothing re: idle), I found the bleed screw completely bottomed out with the idle at about 900-1000. It could not be lowered. Unscrewing it would make the idle would go up. There is slack in both throttle cables; neither are touching their plates. The throttle plate was closed.

I figured that there has to be a vacuum leak somewhere, but I cannot find it after emptying two cans of spray everywhere. I couldn't get a good bead on where the intake bolts to the head, so I wonder if it's leaking at the intake gasket there...or maybe some weird crack on the underside of the intake unit.

I am open to suggestions, thanks

 

Try pinching off the hose to the brake booster.

When you cleaned the upper intake, did you clean the bore of the throttle body and both sides of the throttle plate? Carbon buildup can cause the throttle plate to stick slightly open.

Also stop by a parts store and have them scan for codes to make sure you don't have any current or pending codes that may help you narrow down the problem.

 

Try this as a last resort, just in case someone has tried to use the throttle stop screw to adjust the idle.

Adjust the screw & lock-nut at the throttle shaft, to let the throttle close more fully. That adjustment should just barely prevent the throttle plate from becoming stuck closed. If the throttle was sticking closed in the past because of carbon buildup, that stop-screw might have been used instead of properly cleaning the throttle.

 

Thanks, guys.

I did neglect to mention that I used pliers extensively to pinch off hoses, including the booster hose, as close as possible to the intake.

I shall research the location of this other idle screw & try.that.

I cleaned the hell out of the intake when I had it apart. I may have to do it again, & more thoroughly.

 

I can't find a good picture of that other adjustment screw & now I'm wondering if I remember it correctly...



It around the cable-barrels & springs for the throttle. If the cables are slack, what kind of tab or structure stops the throttle from closing even further? A screw with a locknut might have been there on earlier Accords, or maybe I just can't find a picture from the right angle.

If there's no actual screw, then a sloppy method of adjusting would be to bend the metal tab that hits against a stop. Hopefully some misguided mechanic in the past hasn't messed up that tab.

Or... What about the throttle springs being weak & unable to close the throttle completely? (I guess I'm grasping for ideas now)

Other things to check are the 2 O-rings in the picture. MAP sensor and the proper idle-air screw. If those O-rings are hardened with age & heat, they might leak. But hopefully you've ruled those out while looking for vacuum leaks.

Take out the idle-air adjusting screw & look at the tip. Is it mangled or anything? If it's not right, if it doesn't seat properly into the opening, then it might still be open even when you tighten it with a screwdriver.

 

Maybe the Throttle body gasket is leaking, or the screws that hold it on are slightly loose. Since you can't get the idle speed down you definitely have a vacuum leak. And it's somewhere in/on the intake manifold. It could even be the gasket for the upper/lower plenum since it's a tin gasket.

 

I couldn't find a manual adjustment screw.

There is a definite gap between the plate and both throttle cable/shoe...there's no contact there, and the plate is some thick black material (plastic?)

As far as I can tell, the throttle plate (butterfly) is operating normally & closing fully.

The idle bleed was dirty but not deformed; I cleaned it off with no issues & blasted the orifice for good measure.

I'll have to check those O-rings...though neither the bleed screw nor the MAP unit responded to carb cleaner.

I may just disassemble the entire throttle body & start over with new gaskets. Nothing lowered the idle during my efforts...but I agree, there has to be a vacuum leak in there, somewhere. I'll keep you posted. Thanks.

 

How about an out-of-place O-ring on the idle adjustment screw. It belongs in the big groove near the head, so when you put the O-ring on you have to push it over the threaded part.

If the O-ring is near the point of the screw, it'll prevent the screw from closing all the way. And that won't be a vacuum leak from the outside so it won't respond to carb cleaner.

(still grasping for ideas)

 

Yeah the pic (drawing is deceiving) in how the "O" ring is supposed to sit on that screw. When I had the plenum split on my wife's car (I was cleaning out the EGR port), I used a new gasket, but I also added some Aviation glue to it to make sure it would seal. Having dealt with air cooled VWs over the years, I've found metal gaskets to be hit and miss when it comes to sealing.Double check the hose ends and maybe even the hoses length. I only mention it, as a buddy had a slight miss on his wife's Blazer. Turned out a vac hose ran from the left side to the plenum, and was full of minute cracks you couldn't see until you flexed it. He also found other hoses that were loose on their connectors. Little things like that add up to vacuum leaks and a miss.

 

OK...before I pull this puppy apart: Is there any chance a crudded-up, stuck, or otherwise broken EGR valve could be causing these symptoms? I haven't even looked at it yet.