QuestionQUESTION: My 1988 Mazda 626 with 2.2L started stalling when the RPM gets down to about 1100-1200 RPM. This may get long as I want to describe everything I know about it so far.
This problem is intermittent. It will do it idling in park or when in drive, reverse, neutral. Sometimes it runs fine, other times it stalls. It is not temperature dependant. It has ran fine when cold and at operating temp. It has also stalled at both cold temp and operating temp.
I replaced the air flow meter with a used one but it made no difference. I had the idle air control valve off and it seems to be operating ok. I have tried tapping on this both when it was running good (to see if I could get it to stall) and also when it was not running right (to see if it would idle correctly).
I've checked for vacuum leaks and was not able to find any. PCV valve is good. When it runs right I've tried to wiggle wires and harnesses to try to find a problem.
One thing I have noticed, when driving and the car slows down and hits that 1100-1200 RPM range, I will see the tach drop to zero, stay there for a second, and then return up to the operating RPM and continue running.
When it does stall it always restarts for me immediately. I have never had a problem restarting it. I have never had it stall above that 1100-1200 RPM range.
Should I be looking at the coil/igniter circuit?
ANSWER: I would not suspect a coil or ignitor. Unfortunately, I would suspect the things that you have already checked. When you removed the idle air control valve, did you clean it, or was it even dirty? Also, do you have the a/c on when this happens? If so, it could be that the idle compensator is not working for some reason. You seem knowledgeable enough to know better than that though.
One thing that we mechanically knowledgeable often overlook is the age of the plugs and wires. Perhaps it is simply time for a tune-up. If you know how to use an ohm meter, you can measure each plug wire's resistance from end to end and see if they are within specifications. I believe that 1000 to 4000 ohms per foot is the generally accepted value. Since your #4 wire is about 2 feet long, don't be surprised to see nearly 10,000 ohms of resistance. However, if you see 20,000, then you should definitely replace the wires. Also, look at the spark plug wire connectors and check for corrosion. Insulation on plug wires can break down too, and they may arc to ground or to other wires.
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QUESTION: Replaced plugs, wires, cap and rotor. Also replaced intake boot between air flow meter and throttle body. The boot had cracks that I repaired in the past but to eliminate it I replaced it with a good used one.
ANSWER: Upon rereading your original question, I realized something. You said that the tach will sometimes read zero while you are decelerating past 1100 rpm. This indicates to me that the ignition system has "turned off". This makes the most sense for an automatic since the motor would be allowed to decelerate down to 1100 rpm while the car was still traveling at a reasonable speed. Is the transmission an automatic?
Unfortunately, the reason for the ignition failure is still puzzling.
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QUESTION: Yes, it is an automatic transmission. What are the possible causes of the ignition "turning off"?
AnswerA flaky ignitor or ignition module could do it. The tachometer should get its signal from the ignitor's signal. It is also possible that pick-up coil is failing intermittently. However, it seems like these failures should not be happening at only 1100 rpm. That is the peculiar part.
A sensor with a potentiometer could cause such an effect. A potentiometer can sometimes wear out in one position. This is very common with flapper type maf sensors. This sometimes also happens with throttle position sensors. Unfortunately, a tps would fail at specific throttle inputs, not at specific rpm. Additionally, you've already replaced the maf sensor, so that it probably not the cause of the problem either.
I wonder if the car has more than one ignition circuit. I am not intimately familiar with the ignition system on this car, but Mazda and Ford are both fond of having more than one ignition circuit. All Rx7s have at least 2 ignition circuits. All 85 and earlier Rx7s have 3. Many 80's vintage and earlier Fords have a separate ignition algorithm for start-up than for all other operating conditions. I wonder if your car is reverting to a different ignition algorithm as it nears idle speed. If some part of the system were malfunctioning when the switch happened, then that would explain why the problem only crops up at 1100 rpm. I'm sorry, I'm really reaching here. This is a fairly odd problem.
