Hello there, I’m having some issues with my 1996 Mazda MX3 1.6L 5-speed. I’ll begin by listing the symptoms/issues my car is having, followed by what I’ve done to try and solve these issues.
Symptoms/Issues:
RPM’s dropping to about 200-300: sometimes even lower almost causing the car to stall (oil/engine lights come on like it’s stalled, but engine revs back up) and even occasionally stalling completely. This typically happens when coming to a stop and pressing the clutch in. Also it typically happens after the car has warmed up.
Rough idle: After the RPM’s drop down to that low range (200-300ish) they’ll usually jump back up to about 700(ish) which is a bit low compared to what my normal idle RPM’s should be.
“Pulling” while driving: I notice this most frequently in 3rd gear while going a constant speed (not accelerating) the car feels as if it’s pulling or jolting forward, and as soon as I put some pressure on the gas this usually goes away.
Whistling sound: I can hear a faint whistling sound from under the hood, it’s not very loud and most noticeable right after starting the car.
Power not going to wheels: This symptom doesn’t happen as often as the others but sometimes I feel as if even though I’m accelerating the power isn’t going to the wheels right away, instead there is a slight hesitation before the power goes to them.
Things I have done:
Removed and cleaned the throttle body
Removed and cleaned the IAC (Idle Air Control valve)
Replaced the O2 sensors
Other Notes:
-After some research I read that the cause of this could be a vacuum leak, and when checking under the hood I noticed my air intake hose had a crack in it, which has since been repaired.
-After replacing the O2 sensors the issues did seem to disappear for a few days, but since then have returned.
-My car isn’t throwing any codes
I’m hoping someone here might have some insight/suggestions on what I should check/be looking for as the cause of my issues. And if you need any additional information, I’ll be checking this post frequently and can provide it.
I’d be suspicious of the idle air control valve. It may now be clean, but does it work? There must be some way to test its functioning, but I sure don’t know what it might be.
Does it only do that when you press the clutch in? If you aren’t sure, next time that happens try putting it in neutral and letting the clutch out. The clutch may be unrelated.
Wandering rpms can be due to a host of things. One to consider if your engine has an air bleed screw to set the rpm, that someone has adjusted it to compensate for another problem. That has to be set in a narrow range or you’ll get this symptom. It isn’t for correcting other problems.
No air bleed screw? Very well could be a vacuum leak. That would be consistent with it being worse when the engine is warm. Ask your shop to use a stethoscope to listen where the whistle sound is coming from, might provide a clue. Finding the source of a vacuum leak varies car to car, but most mechanics have done it so many times they can do t find the problem in their sleep. It takes a systematic approach. If you feel lucky, check the brake booster. It could be leaking vacuum. Or the hose could be split. That’s the biggest vacuum-drawing device in the car probably.
One way to check for a possible Idle Air Control valve problem is, once the engine has warmed up, and the idle problem occurs, open the hood while the engine is idling, and take the handle of a screwdriver and rap on the IAC valve.
If the engine idle speed changes when doing this, replace the IAC valve.
Was there a code thrown and someone convinced you that the 02 sensors were the fault.
02 sensors would never cause these symptoms.
I would search for a vacuum leak also. You can do this yourself to pinpoint that whistling sound you hear.
Use a short piece of old garden hose. Hold one end to an ear and use the other end to move around different areas under the hood. As you get closer to the whistling it should seem louder in your ear.
Be careful not to get the hose…or any body parts in any moving belts or pulleys.
My vote is with Yosemite about checking for a vacuum leak. The whistling sound is probably just that; a vacuum leak.
Any vacuum leak will cause a low or rough idle and the Idle Air Valve cannot compensate for things like this.
One way to check for a possible Idle Air Control valve problem is, once the engine has warmed up, and the idle problem occurs, open the hood while the engine is idling, and take the handle of a screwdriver and rap on the IAC valve.
I do this when my 302 V8 equipped Ford truck (with a carb) gets the “fast-idlies”. If a rap on the carb with a screwdriver handle slows the idle speed back down to normal, I suspect a sticking throttle plate, and time to clean out the carb.
Edit: Whacking stubborn gizmos seems like it has always been a good solution for mechanical gadgetry. Apollo 11 was the first time for a moon walk, but folks back home on Earth complained the camera didn’t show the event very clearly. I think it was just a simple low resolution b/w tv camera. So on Apollo 12 NASA put some effort into getting a good quality color camera up there. But when they got it on the surface of the moon, it didn’t work. So the astronaut in charge’s solution? Give it a whack with a hammer! He’s standing there on the moon hitting the camera with a hammer!! … lol … That didn’t work unfortunately, the problem was the camera accidentally got pointed directly into the sun during the initial set-up and it burned out the image sensor. But you got to hand it to that astronaut that whacked the non-functional camera a good one with his hammer.
The IAC valve assembly actually consists of the valve body, the valve itself, and the motor that operates the valve in response to the ECU command. the motor is the little black part off to the side of the body. it’s possible that the valve is now well cleaned but the IAC motor is not functioning properly. You might want to stop at the Mazda dealer’s part window and ask the guy there nicely to print a copy of the test procedure for the IAC valve operation.
That’s not to suggest that a vacuum leak elsewhere isn’t a possibility, but the IAC is sort of a controlled air leak in that it controls the air being drawn into the induction system under no-load conditions. If it’s malfunctioning, it can act like a vacuum leak.
I just thought of an idea: if you unplug the IAC motor and nothing changes, that’s a pretty solid suggestion that the IAC motor has failed.
@Yosemite
I read online someone having these symptoms and they were told it could be due to faulty O2 sensors, and after checking mine I noticed they were indeed faulty. I thought perhaps the air:fuel ratio might have been off causing the engine to idle roughly at times. Either way they needed replacing whether it was part of the issue or not.
I’ll try that trick to finding vacuum leaks, as based off sight/touch I haven’t found any yet.
Could this be a clutch issue? I’ve noticed my clutch isn’t engaging quite as noticeably as it used to (if that makes sense) it’s not “grabbing” strongly and it engages at about the last 2 inches or so of letting out the pedal.
@Yosemite
Yeah, I think a new clutch may be in the near future for me, luckily it’s not too expensive for my year/model. And I tested the voltage of the O2 sensors when heated up and they were far from where it should have been.