Irregular idle on a 87 Accord LXi

DAD1999

MEMBER
1987 HONDA ACCORD

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 there are NO codes set.
Any suggestions?

5 Replies

BRUCE HUNT

MECHANIC
3,753 POSTS

You have done a lot so far. Have you had anyone take off or work on the intake manifold? Gasket could be leaking and causing this erratic idle. Computer gets confused on idle air mixture regulation.

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Wednesday, August 30th, 2006 AT 11:21 AM

DAD1999

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3 POSTS

I have tried detecting a leak using carb cleaner and not found any. I did just replace the PVC valve and this helped but very little.

Thanks!

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Tuesday, September 5th, 2006 AT 5:56 AM

BRUCE HUNT

MECHANIC
3,753 POSTS

There is a smoke test that can be done to the manifold to test it for leaks.

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Tuesday, September 5th, 2006 AT 3:45 PM

DAD1999

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3 POSTS

Thanks for the tip!
I was hoping not to spend more cash at the shop. I’d like to try a few more back yard options first. 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 am debating removing the throttle body for better cleaning.
More suggestions?

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Wednesday, September 6th, 2006 AT 5:44 AM

BRUCE HUNT

MECHANIC
3,753 POSTS

That is really not a bad choice. It is under $20 to replace the intake manifold gasket and is the carbon deposits are as you mention you could certainly do no harm. Good luck!