1987 Accord LXi. Car has the 2.0L FI engine with 170K miles. Compression is 170 PSI on each cylinder. Idle when cold is irregular. Once started the RPM hits 1500 slowly dropping to 1000 (over about 10 sec) then drops to 100 and almost dies. The RPM then rebounds back to 1000 and continues hunting for about 1 minute. The idle is still rough until the car is warm and seems rough (vibration) 80% of time at operating temp. while in drive. I have checked for external vacuum leaks, cleaned the IAC and EGR. I have new wires, plugs etc…Over the past year I have replaced fuel injectors, fuel filter, fuel pump and tank. I have the service manual and have measured the coolant and intake temp. sensors that send a signal to the ECU. They seem to be close to the temp/resistance curves in the book. I checked the fuel injector ballast resistors that should be 5-7 Ohms and are measured 12 Ohms. I don’t think these are the problem even if slightly out of spec.. Last weekend I disassembled the distributor to check if oil was obstructing the ‘Cyl’ and ‘TDC’ pick-ups for the crank sensor. They seemed clean. My feeling is a missing/false signal is being sent to the ECU and causing the hunting condition. A mechanic said look for vacuum leaks and question the valve springs and valves. Also, no codes are set.

Update: I have replaced the PCV valve and cleaned the ports and hose. It seems to idle better when warm. But, I still have the minute or so cold idle problem. I have cleaned the IACV and tried to isolate it from the problem but to no avail.
I just cleaned what looks like an idle bleed screw on the front end of the throttle body. The 1/4" diameter needle and seat were covered with black deposits. I brushed the bore along with carb cleaner then blew it clean with compressed air. The car idle better at operating temp. but still has a high idle 2000 at first start(car is overnight cold) for15-20sec then drops to 50 and dies. I must tap the accelerator to keep the car running as it cycles through the high and low RPMs for about a minute or so before it clears up. I am debating removing the throttle body for better cleaning.

 

Hello Dad

First off,, Welcome to HAF.....

for the idle hunting, remove the top lid for the fast idle valve 2 phillip screews, get a screwdriver and tighten the inner black valve inside the housing, tighten it till it bottoms out , put the cover back on and see if that help the cold rpm surging

any codes in the computer ??

 

Thank you for the tip. I will try setting the poppet seat when the IAC valve is cold. The computer is not listing any codes as of yet. I have unplugged various sensors when debugging and noticed the appropriate codes being set in the ECM. I did clear the codes as I progressed through my testing.

 

another thing that came to mind could be a bad tw sensor......

Oh,, it is the FAST IDLE VALVE i want you to remove the top cover and
TIGHTEN THE INNER VALVE not the IAC valve

 

Thanks for the added info. I am not sure of the fast idle valve location. I was thinking the the fast idle valve was the 1/4" diameter needle valve above the throttle plate. This needle valve runs in horizontally, is set off the seat by 1.75 turns and has an 'o'-ring on it.

 

Let's all get on the same page. BTW have you tried pinching off the PCV line to see if the idle smooths out? Could be a bad PCV valve.

 

Yo Dude,, thanks for the pic,,,,,,,,it should make it a lot easier to locate the fast idle valve now ..
and the suggestion of the pcv valve,, ( good 1 )

 

Thanks. I replaced the IAC and the car runs much better. The idle is smooth when hot and at cold it is much better. I have replaced the PCV and cleaned the hose. However when I was installing the new PCV I was not sure if the new one was as good a quality as I have seen in the past. So... I will try and pinch the hose when cold and see if the PCV is adding to the slight rough idle when ice cold. BTW will the ECM learn as I drive in this 1987 modle or is it to primative? I may have to drive the car a while to let it learn if the ECM does learn....