Idle issue when engine is warm
 

My wife has owned our 1998 Accord since it was new, it now has almost 176000 mile and this is a new one for me. Today immediately after fueling up I notice a really low idle when stopped. I drove into work and it ran fine when at speed. I didn't notice any issues on the highway but when I had to stop the idle would drop to 500 Rpm or less and it acted as though it wanted to stall. It would also hesitate and studder a bit on take off but once the rpms were above 1000 it would run fine again...until I slowed again. When i went out for lunch it started and ran fine until it began to warm up and then the issues resumed. The same when I left to come home. Only seems to be an issue when the engine is warm. I checked the vacuum lines and the all appear to be fine. I also looked for an obvious sign that the manifold might be leaking but could not visually see anything. With Christmas approaching I really can't afford to take it into the shop but with some help with the diagnosis, I am a pretty good shade tree mechanic so I am sure I can repair it. Just not that good with the diagnosis piece. Any help would be very mush appreciated.

Idle speed is controlled by the Idle Air Control Valve (IACV). The IACV is controlled by the ECU to maintain a stable idle. IACV is a simple on/off solenoid valve w/ spring-close action that is rapidly modulated by the ECU to maintain idle. When load increases more bleed is allowed which ECU increases fuel to maintain fuel/air ratio.

Fix is cleaning the IACV inlet screen, valve movement, inlet/out ports, throttle plate (both sides), and throttle bore around throttle plate. Use throttle body cleaner.

A shop manual is handy to find the IACV and get pics. Check autozone online manuals for some free quick info.

good luck

Ok I have replaced the IACV, I have also replaced the Intake, Plenum, and EGR gaskets. I also made sure that the catalytic converter is not clogged. Still having the same issue and it seems to be getting worse. It idles as normal when I first start it but the second the engine begins to warm the idle drops and wants to stall. the engine also seems to load up so when I first press on the gas it hesitate and sometimes stalls. When I get the RPMs up I can hold a stead rpm with the gas pedal...no surges or pulsating.

I would appreciate any additional help. This is driving me nuts.

Thanks,
Dan

Since partial throttle produces a stable idle, the engine is starved for air. Was throttle plate and bore cleaned thoroughly?

Have you checked the IACV is functioning? solenoid works when 12V is applied.

Did you reset the idle rpms by disconnecting the IACV and adjusting the air bleed screw (TDC of throttle body intake)? This should be adjusted to produce about 550 +/- 50 rpm. You will need to reset the ECU (pull backup fuse for 20 secs) to clear check engine light which appears when you disconnect IACV.

good luck

Going to try this today. New IACV, new coolant/air hoses/ tune-up, fuel injectors, gas tank, charcoal canister, TPS, MAP sensor, brake booster, radiator coolant (full flush Asian blue, have been running it for years, 0 air bubbles every time), new gas cap, easy flush to trans, etc. Randomly started this crazy idle had P0505 coded, cleared that up, cleared up the air/fuel ratio codes, lead to map sensor, 3rd one (4th for the car), no code for MAP yet, idle still going crazy 1200-2200. 98 DX Model ( pain in the butt, DX has a few varied parts from all the other 98-02 models). Even picked up the manual cheap this week finally. Will report here if this process doesn't clear the issue.

Curious to know if you have anything new to report on this issue,
because I have been experiencing the exact same symptoms
on my '92 Accord off and on for quite some time now. I've looked
at a lot of threads describing this exact issue with older Honda's
both on this board, and on other similar auto tech boards. It seems
to be a common issue for sure, yet the experts don't seem to be
able to offer any really clear and useful advise that leads to successfully
resolving the issue. It's frustrating.

Im no expert but..
 

I’m no expert by far but what I’ve noticed with messing with pretty much everything on 97 Honda Civic and 94 Honda Accord to tackle this low idle issues that drives me insane. There is a sweat spot on the idle screw if you can get it in sync with your IACV. Your idle won’t drop at a stop when your car is warmed up. Also aftermarket IACV are just crap they cause vacuum leaks you will get symptoms like your rpms will jump up and down also don't mess with throttle plate screw! That will also cause vacuum leak even if you adjust your tps sensors voltage around it. What I did to solve my idle issues in both my Honda's I disconnected the iacv after my fans had came on (make sure your rpms are not going up and down) then I adjusted the screw till I got 450 it was full turn and a 1/4 from bottoming out for me. After that I put some e6000 inside the idle screw and pulled radio/back up fuse for about 10 minutes. Then I didn’t experience any idle issues even solved my high load idle issues I hope this can help.