QuestionQUESTION: The car has automatic transmission, 1.8 engine twin carburators. When the car started it was hard to keep it running and would not run without patting the accelerator pedal for about 4 minutes(until engine heated up) then it would idle down.
The two wires(black and red) coming from the air temperature sensor were disconnected from the harness and the two wires on the harness were connected together and now the car starts up and runs immediately.
The problem is that the engine will continue to run at fast idle even after the engine heats up. It will not idle down.
I would appreciate it if you would let me know what you think the defective part(s) is/are or what other problem it could possibly be. Thanking you, Frank
ANSWER: Frank,
I'd check the thermo-valve that is in the engine coolant passage. I'm fairly certain it is at the thermostat housing on the 1.8liter. The thermovalve should open or close as the coolant warms up. Basically, it is a vacuum switch that either gradually allows vacuum to flow or gradually stops the flow. The other end of the vacuum line will be routed to a diaphragm that pulls on the choke. This works together with the bi-metallic spring in the electric choke housing.
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QUESTION: Good afternoon Gary:
Ref. 1985 Honda Prelude twin carbs:
The following have been checked out and are in good working order:
Base Plate Insulators
Electric Choke
Choke Pulloff Diaphram
Thermo Valve
All visible vacuum lines are in excellent condition.
Everything is hooked up correctly but idle problem still remains.
When the car is started I have to continuously "pat" the accelerator pedal for 4-5 minutes until the engine warms up. When the engine warms up the idle levels off at about 1800 rpm. When the idle screw is turned to where it idles at 800 rpm the car operates perfectly when hot. When the car is shut off and restarted dead cold with the idle screw at the 800 rpm setting, it is harder to keep the engine running until it warms up but after it warms up it idles and runs fine.
My major problem it getting the engine idle to function properly from dead cold. Please advise as to what your thoughts are on this problem. Many thanks to you. Frank
ANSWER: Try carefully spraying the surrounding areas with a combustible type carb. spray. Maybe you have a vacuum leak that is sealing up after the under hood temps are warm.
How did you check the thermo-valves?
How did you adjust the mixture? The only accurate way of adjusting the mixture is to use a gas analyzer.
Let's not overlook the obvious things like spark plug heat range, valve adjustment, rotor button condition, cam timing, and base timing. Fresh fuel too!
Another easy check would be the engine thermostat. One of the Prelude race cars I sponsor had some poor engine performance. When the car owner replaced the thermostat (like I previously recommended) the car ran much better.
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QUESTION: Good morning Gary:
Thanks for your reply and I need to ask for clarification on something please:
1.If you were checking the thermo-valves how would you do it?
2.You lost me on the part about adjusting the mixture and using a gas analyzer to do it.Please fill me in on this.
We are very close to getting the 1985 prelude right and the only remaining
evident problem is getting the engine to run when started from dead cold. As mentioned, after about 4-5 minutes of patting the gas pedal with my foot it levels off and idles perfectly. The car drives very good, never hesitates going up a steep mountain road or on a straight road driving it 75 mph. Getting it to run when it is first started is the hair pulling problem.We are so close and yet so far away from having it right.
Would appreciate your reply and thank you again for your patience. Frank
AnswerA gas analyzer is a smog machine. In an earlier question I described the thermovale inspection
The thermovalve should open or close as the coolant warms up. Basically, it is a vacuum switch that either gradually allows vacuum to flow or gradually stops the flow.
