QuestionQUESTION: Hi Ted, I'm a fellow All Experts myself (in a different category) and after answering questions over the past few years thought I would ask one myself.
I have a semi retired 1978 Toyota Corolla Wagon that is coming out of retirement. I would periodically start the car and move the wheels so they would not get a flat spot.
I went for my smog test and was certain I would fail because there was a noticeable fluctuation in the idle speed. The car passed at regular speed but failed at idle.
I went ahead and replaced the fuel filter, air filter (which was very dirty and when I hit it against the driveway A LOT of small black particles came out), a couple of the vacuum hoses, (others I had replaced the last time I drove the car and they all looked fine).
And then I took off the EGR valve. It was filthy with what I believe are carbon deposits. It took me several hours to clean both the EGR valve and the section on the engine block that connects to the EGR valve.
When I put everything back together again the car did run better, first it runs smoothly when cold, but then when it warms up, the idle heaves back and forth, faster and slower, just as before, but not as badly.
I tried adjusting the two screw on the carburetor, the one closer to the windshield can only go so much in one direction and then the car will stall out. Once I set that screw, I tried the other screw but it did not seem to do too much no matter which direction I turned it. There was a little bit of change in the idle, but not that dramatic.
Do you think the problem is the carburetor, the EGR valve, a vacuum leak, or might I have some hoses incorrectly connected? I'm in California and we have stricter smog rules so I will need to have the EGR valve working.
I was thinking of bypassing the EGR valve and seeing if that was the problem. I would love to see pictures of another 78 toyota corolla wagon 5 speed engine and all the hoses so I can compare my set up to theirs.
Any thoughts?
ANSWER: Unfortunately I have no printed or electronic illustrations for a car this old. the carburetor has an air/fuel mixture screw in the cast iron base, there is also an idle speed control screw to the left, the screw that you are turning with no effect on the engine speed is the fast idle screw which only adjusts fast idle when the choke is closed. To verify EGR operation you should do the same test that the smog inspector uses, apply vacuum to the valve to see if the engine dies at idle. If it does the valve is working correctly, the inconsistent idle could be caused by an intake gasket leak or a carburetor base gasket leak or a carburetor malfunction. You can check for vacuum leaks by spraying around the intake manifold using a can of brake cleaner to see if there is an idle speed increase, this would indicate a leak.
---------- FOLLOW-UP ----------
QUESTION: I was told that the problem is probably related to the idle air control valve.
If that is correct, do I have to have the entire rebuilt to fix this problem and can it be isolated and repaired? And what type of cleaning tools are available to clean out built up carbon deposits in the lines that go from inside the engine to the EGR valve?
AnswerThe carburetors have an idle solenoid on the side it has an electrical connector on it, remove the solenoid and make sure the rubber O-ring is on the end of it, I nt he past I have used a piece of wire/coat hanger to clean out the passage there may also be a kind of a miniature rotor roooter that you can attach to a drill.
