I'm trying to correct some recently (last couple months) idling problems on my carbureted 87 honda. The car has 270k miles on it and I've had a lot of fun keeping it going/learning about automobiles with it. I've replaced the clutch, water pump, rebuilt the power windows and locks, replaced the fuel tank pump, installed new breaks/calipers, tie rods and CV joints and fixed some electrical issues all with the help of 3geez! Even with those successes I cannot adequately address my current issue. I will outline the symptoms below, describe what I've done so far and then make some guesses about what I should do next based upon everything I've read here in the threads: Idle Adjustment & Emissions Help, includes PCV and Black Box info, Vacuum Gauge Read, What Does It Mean? And Serious Problems, Loose booster Venturi/carb Icing/Throttle Stick/Dieseling and in my carefully examined repair manuals (Chilton 73-88 and 84-95 and Haynes 84-89).
I would really appreciate advice and perspective. I am a student (biomedical) so I do not have infinite free time and would prefer to start diagnosing at the most likely places. Here are the symptoms as I know them:
A) Engine idles lowest at 1100 rpms and often higher at 2500 rpms. When decelerating and coming to a stop the rpm will often increase further to 3000. The rpms do not increase unless the clutch is engaged. If the engine remains in gear the rpms behave normally as one would expect.
B) The rpms do not decrease when the clutch is engaged while shifting gears or when the pressure is removed from the gas pedal.
C) The engine will occasionally diesel upon shut down.
D) Very occasionally (3 times total) the engine fails to idle. When the clutch is engaged and the car is decelerating the rpms will rapidly fall and the engine stalls. The engine will immediately restart as long as plenty of throttle is given. This symptom goes away with a few restarts and then the car idles around 1100 rmps.
E) Occasional surge and galloping while accelerating in the first and second gears.
High RPM that doesn't decrease with clutch engaged or gas pedal released.
Surging/galloping during accelerating in first and second gears.
Stalling of engine during deceleration.
My attempts to address issues:
1) Replaced spark plugs, wires and air filter. Checked all coolant and oil levels.
2) Adjusted the throttle cable. It is NOT to specifications: if the throttle cable is tightened to recommended deflection 3/16 to 3/8 of an inch the engine races at 5000 rpm. The throttle cable currently has ~2 inches of play in it (as I found it originally).
3) Adjusted the idle speed adjustment/throttle stop screw. This had no discernible effect. Rotating it both clock and counterclockwise did not change the idle speed.
My plans for correction:
4) Check vacuum lines with a vacuum gauge checker. I have one ready to pick up from Harbor Freight. I will replace failed lines and solenoids. Any information as to what I should check first or what is the best reference material would be greatly appreciated.
5) Check the throttle plates to see if they open and close w/out sticking (I need to figure out what/where these are).
6) Remove the air filter, gold screen and look down the barrels (location unknown to me) and inspect to see if the secondary butterfly valve is open. Should this be done with the engine running and an assistant to run the throttle (I will be wearing safety glasses).
7) Follow the test procedures in one of my manuals and conduct the tests for the choke opener and fast idle unloader.
Should all these fail: purchase a weber carburetor (DGV 32/36), but the adapter plate, bolt it on and throw away "40 lbs" of emissions controls. Which I would be fine with as I am not concerned about emission controls (should I be? Car is and will remain registered in Alaska).
Please let me know if I am barking up the wrong tree or making errors. Questions, comments and opinions appreciated.