Talked to 4 reputable mechanics, no help, problem persists. Here are the facts: a few months ago, the check engine light came on. This code came up: “P0506 - idle air control revolutions, permanent lower than expected” but beyond scope of oil change shop I was at so I immediately drove to a mechanic.
Mechanic 1: Code did not come up again at mechanic’s shop, check engine light was off, and mechanic said there was nothing to do at that point.
Mechanic 2: Later, a mechanic on the phone told me the code could mean the following: a leak, idle control valve is bad, dirty tustle(?) body (not sure if that’s correct - my handwriting is pretty bad on the notes I took), or poor electrical connection.
Current symptoms: A few weeks later after a short stop, car would not start: it would start to crank but would not turn over. When it did turn over after the third or fourth try, it was idling very low, and stalled out when I put it in gear. I waited 20 minutes, restarted with the very same issues repeating. Check engine light has not come back on at all.
Mechanic 3: Took it to a mechanic who said if the problem was not occurring at the moment, there is nothing he can do. He changed the spark plugs.
Symptoms persisted: A couple of weeks later: trouble starting after a short stop, stalled when put in gear, waited a while and then it started up fine. When driving, it seems to be idling lower than usual and feels as if it is about to stall, but has not (yet).
Mechanic 4: Mechanic said the code is meaningless and that if the car is not replicating the problem at the time they are in possession of the car, they can’t diagnose the problem. So I told them to keep the car all day to run their errands. The problem occurred for a just a moment just like I said for them (after a short stop) but that it started up again shortly thereafter so they could not diagnose the problem.
Mechanic 4 said the idle is too low at times but felt it was also too high at other times. They did not actually look at anything under the hood, just connected gauges. Other hypotheses that were proposed by the shop: a fuel pump problem (but can’t tell me whether that is or is not a problem - numbers read fine on gauges while car in their possession), or a thermostat problem. The shop is going with the thermostat problem but my confidence is low since learning they never checked the idle control valve or looked for gunk, just connected gauges to read current numbers on an intermittent problem. The computer code does not show in the history, according to current mechanics, but they insist there is nothing wrong with computer because “there can’t be”.
Rationale: for problem being with the thermostat given by the mechanic (not sensor): he drove about in 100 degree heat, said he used the car during the day and parked it in the sun, and the temp. gauge shown to the driver in the cab should read closer to the middle temp, and it was reading at halfway between cold and the middle temp. At garage, 184 degrees and he thinks it should have been well over 200 degrees.
My questions: 1) why won’t anyone check the idle control valve or look under the hood for gunk in potentially problematic places? 2) are those codes really meaningless? and 3) what are possible problems and why do you think so? Thanks so much