I'm troubleshooting a friend's car, I've searched the archives and I haven't seen this combo... maybe someone else has:

Car stats:
'91 DX HB D15 motor DPFI and 4spd manual tranny

Problem symptoms:
After start (cold) the engine idles at constant 1000rpm (no tach, so I'm guessing here, but its definitely higher than norm 750)
After warm, idle surges btwn 1000rpm and 1200 rpm
Initial check engine light came on, displayed code 04 (crank angle sensor), but after resetting the ECU no more codes thrown until car driven at highway speeds. Then check engine light returns with code 04.

Things checked:
reset ECU - no more code 04 thrown until driven at highway speeds
crank angle sensor - disconnected the plug, measured it with a VOM and found it in spec (430 ohms) - cleaned contacts and reconnected
vacuum lines - checked for cracks/leaks none found, they look good
intake air system - checked for air leaks - none found
idle adjustment screw - frozen solid, can't budge it with a big straight blade screwdriver... that's another problem... currently soaking with penetrating lube...

Questions:
Is the code 04 (crank angle sensor) related or just another symptom of another problem?

What other sensors/systems can be causing the idle problems and not throw ECU codes?

The idle speed dashpot appears to do nothing to the idle while the engine is running even when I manually push the plunger in/out... is this related to the surging problem or the stuck high idle?

Thanks in advance for the help and/or suggestions.

 

bump - still looking for help

 

I found the same issue on a my 1.6 MPFI sohc. In my case, I traced it down to multiple issues. First was the O ring was missing on the distributor shaft. Second was the wires on the internal ign. of the distributor. I followed the manual (Helms) and traced it back to these.

Check the FAQ for better details.

Note to you: MPFI will make a world of difference. I have a IM and TB for cheap, if you want. Good luck.

 

Found these too:

MPFI - https://honda-tech.com/zerothread?id=945557

ECU Codes and Troubleshooting

https://honda-tech.com/zerothread?id=468260

 

Thanks for the info, I found those links in my original search which is how I checked out the crank sensor and found it OK.

Can you tell me if the code 04 (crank angle sensor) is related to the idle problem, or just a symptom of another problem?

Also, does anyone know of, or can point me to a list of, known idle problems that don't throw codes?

BTW, the car isn't mine, just helping a friend troubleshoot his, thanks for the offer of the intake, I'll pass it on to him.

 

To loosen the idle screw I first chipped away all the compound stuff that covers the screw. Then I took my solder iron and put it on the compound around the screw and I also used the heat and the tip of the iron to dig the compound out of the screw slot so I could get a screw driver in. I hope that helps.

 

I managed to get the torque seal off the screw head, but the screw seems like its either jammed or its corroded solid to the TB. Its not my car and I don't want to permanently disable it or have to pay for a new/used TB...

Someone else told me that this screw should never be adjusted because it will throw the TPS adjustment out of whack??? Any truth to this Honda-Myth or what?

Anything about the intermittent code 04???

Thanks!