OBD0 1988 Crx HF has rough idle with headlights on.

I watched some videos by Eric the Car Guy on Youtube and his website regarding honda idle issues, and sorry if this seems like a lame plug, but he's pretty good at explaining honda bouncy idle issues.

He says

#1 check coolant level and bleed the air out ( I know weird, I didn't guess that one either)
#2 he says, tap the IACV with a screwdriver handle while running to see if it affects the idle if it does then your Idle Air Control Valve is having issues.
#3 Check for any other sources of additional air into the intake, (vacuum leaks)
#4 Check and Tighten Fast Idle Thermo valve tension. Its got a spring and a washer type setup, the washer is threaded and has a tendency to back out causing a continuous leak of air into the intake and a slightly high idle speed. This throws the ECU / IACV idle control loop out of wack and can cause the surging idle. (check that one last I believe)

I hope that I got that in the right order but, those are common causes of bouncy idle on hondas according to eric the car guy. It sounds logical to me.

 

Mine was a faulty ignition coil. I replaced that, bled the coolant and cleaned the engine ground and it went away.

 

i still haven't reduced my bouncy idle issue... procrastination I guess. so your ignition coil caused a bouncy idle??? Man these Honda's are finicky ... who would have guessed? my coil is a little Jerry rigged come to think of it, I bought a discounted one online and had to modify it to fit into my distributor so perhaps that's my issue too. I'll try it and let you know.

I also have never adjusted my valves but they sound fine no ticking noises.

I did check my ELD signal at the ECU pins via the instructions and they were just barely within specification so I am a little suspicious if the ELD. The coil is easier to get my hands on and replace so I'll do that first.

Thanks

 

Wouldnt hurt to clean your throttlebody while your at hit it w carb cleaner, scrub it with a toothbrush, spray it and wipe down w a rag...done. real easy and underestimated at how much good it really does.

 

Sorry I haven't been checking back on this thread, I cleaned the TB really good so its probably not that, but maybe I'll clean it again, its so easy to do.

 

as an update, I parked the car and started driving my van again. Now its sitting waiting for brakes, cv boots, shocks, suspension bushings, water pump, timing belt etc etc. So when I get those pieces finished, I will work on tuning the engine idle issues. I have a new ignition coil on order so I'll soon find out if that is the cause.

Its just weird how the idle becomes unstable when I have an electrical load like running the headlights or radio. Perhaps its just the IACV sticking or slow responding to ECU signals. I cleaned the one on there really good and I believe I checked the winding resistance etc. I have a couple other used ones I can swap on there.

 

I might be your " IACV " try a new battery tough I had the same issue and I bought a bigger battery and problem solve . Good luck !

 

I have a 88 Hf too, I think the ECU is designed on the HF to do a low idle, comparing to my other Si's.,,,,, to save fuel…the new hybrids have autostop…..but the old ones had ecu to correct and low idle. Save MPG this way/

 

Ok, I recall the HF has a lower idle speed than the DX and Si models, yes, most likely for fuel savings. So, are you suggesting the ECU is trying to adjust idle to compensate for electrical loads and causing a bouncy idle?

I read a good article about honda idle problems and they suggested the cause is when there is excess air bypassing the throttle it causes the engine speed to exceed 1100 or 1200 rpm, at which point the ECU senses the throttle closed via the TPS signal, so ECU cuts fuel off completely to save fuel and also reduce emissions ( because it believes the car is in deceleration with high rpm and closed throttle )...

The idle immediately drops lower than 1200/1100 rpm due to fuel cut at which point the fuel injectors are turned back on by the ECU. ECU is sending correct PWM signal for the factory idle speed however, excess air from vacuum leak or other source of unmetered air causes the idle to surge above 1100/1200 rpm again, at which point the fuel is cut again by the ECU.

For me the weird thing is, my car only usually tends to do this bouncy idle problem when I run my headlights or other electrical loads. My base idle is definitely above the factory setting for the HF. My car idles pretty close to 1000 - 1100 rpm all the time even without the bouncing/surging idle. So perhaps when the ELD senses high current draw, it tells the ECU to bump up the idle and also field signal to the alternator, this causes engine speed to cross the fuel cut-off point, and so begins the bouncing idle instability issue.

My car does not have any other load signals to ECU for engine speed compensation, such as power steering. My car came with A/C but I have removed it as it was non-functional and added weight. I think running the A/C would have also triggered a bouncy idle scenario as well. I think the ECU gets a load signal from the A/C low pressure cut-out switch which energizes the A/C compressor clutch (this would increase an engine load & ECU would try to compensate idle speed ) I suppose I could play with this by finding the signal wire and jumper it to see if the bouncy idle occurs from A/C signal to the ECU.

I have a strong hunch the ECU is trying to raise engine RPM from load sensing and then causing fuel to cut off/on at idle. Most likely there is too much air bypassing the throttle plate somewhere, thats issue#1, then I suppose setting the correct base idle will help keep from crossing the fuel cut RPM.

What do you guys think?

 

I have the same issue with my 89 dx, when the engine gets hot it will bounce up and down from 1100 to 1500, i also am procrastinating on fixing it but i need to clean my throttle body so i mine as well do that too.

 

Well, finally, one day I found what looked like an idle adjustment screw in my driveway. I checked my TB and it was from my honda. I put it back in and adjusted the idle.
Since then I have hardly had any issue with the engine idel bouncing around with the headlights on. It seems like if your idle is adjusted too high with this screw, then
the car will develop that endless up down idle surge. I think a little bit of medium thread locker on this screw will help keep it set right.

The only other thing that I can say would cause the idle to increase is a vacuum leak or sticking IACV.

Dave