Lately my engine has sounded kinda... odd. At idle in Drive and Park the engine sounds like it's "uneven". It's hard to describe, like instead of a consistent sound, it seems to speed up and slow down. The best way I can describe it is like the effect you get as spin something around with a weight on the end, and watch it slow down as it nears the top of it's rotation and speed up as it falls back down. The sound is consistently slower than engine speed.
I've also noticed the idle changes slightly when I depress the brakes, but I think that's normal. Where should I start looking for the source of the issues, vacuum lines? It seems more noticeable after I've driven it long enough to warm up the engine but I can notice right after starting the car for awhile. Oil is (As always) fine. Ideas? I have a Check Engine light for a Code 42 (Vehicle Speed Sensor) but no other codes. Car also drives normally and gets 30mpg mixed driving (1.6L/3speed)
No ideas or just a crappy description? The variation seems slower than idle. I don't notice it at higher engine speeds but that could be due to road/engine noise.
Do you have a tach? Can you see the engine speed actually changing up and down? From what I understand the sound changes with engine speed right?
Could it be any of the accessories making the sound? Water pump, power-steering, alternator?
Something funky with the Idle Air Control valve (IAC)? Like the ECU constantly trying to adjust the idle speed?
Depresing the brakes will change idle, because vacuum is used by the brake booster.
sometimes when the primary O2 is getting old and responding slowly your idle can do that. feels like the idle is cyclically speeding and slowing as if someone were adding and taking away throttle just barely. if you were to map the rise and fall it would be a long sine wave?
I have a 96 1.6 auto too. I had the same problem . I installed a new distributor cap and rotor that did the trick . New plugs would help too. I installed bosch plus 2 platnums and a new pcv valve.
corolla615- Beware of Bosch plugs. They are cheap for a reason...!! You can get good NGK's for just a little more and its well worth it. When you get wacky symptoms like cjrocker you'll know those plugs are done, and they will be within 5k miles.
I have no tach which makes diagnostics a bit harder. the A/C compressor is not engaged, and the P/S pump is at an idle as is the alternator (no lights, or heater fan on). I considered the IAC, given the car is a little hard to start when it's cold, but I've not seen it go erractic; when it's an issue it just idles too low. Not ruled it out though, but seems unlikely.
Quote:
Originally Posted by Bitter
sometimes when the primary O2 is getting old and responding slowly your idle can do that. feels like the idle is cyclically speeding and slowing as if someone were adding and taking away throttle just barely. if you were to map the rise and fall it would be a long sine wave?
I've been wondering about that, given the sensor is possibly the original. I would say that about describes it. I'll have to try that first.
Also, the cap, rotor, and wires are about a year old. The plugs are fairly new (within 10k) Densos. PCV seemed clear when I examined it.
If the idle raises when you depress your brake pad, then there is a possibility that you may have a vacuum leak or an intake leak. Check the hoses on your intake and check your PCV valve. Those are like $1.89 from autozone to replace.
If you have access to an air compressor, then you can do a leak test. Take off your intake pipe from the throttle body, and then you need a worm clamp, and a thick garbage bag. Fold the garbage back and cover the throttle body and wrap it with the worm clamp. Next you would disconnect either of the two vacuum lines from the intake manifold going into the head. Make sure you disconnect from the head side. Spray air into the vacuum line, and listen for any air leaks. There is a chance that air is leaking from the intake manifold gasket as well as the throttle body gasket. There is a main vacuum source from the brake booster to the intake manifold. If you depress the brake pedal, then intake pressure is increased raising your idle. If there are no vacuum leaks then the idle should stay the same (900-1000rpm's).
As far as noises, the power steering pump will make a whining noise especially if the fluid is low. If the fluid is low, start filling it with dextron III automatic transmission fluid. And sometimes if the pully bearing gets worn on the alternator, it will make a funny noise as well.
SO why dont you know? Have you done your normal maintenance? DO a leakdown test to see what the internal condition of your engine is.
-SP
I've done my maintenance, but the car is 17 years old with a 162k on it, and I've owned it for 7 years and about 30k of those. Bought a new O2 sensor today but didn't have time to put it on. Also observed some chaffing on the wires and wire harness near the connector that is mounted on the fan shroud.
I will be sure to do a leak down test on the vacuum hoses.
I will be sure to do a leak down test on the vacuum hoses.
Just to clarify it just an intake leak test. A leakdown test is done by using a leakdown tool that installs in the spark plug holes, sort of similar to a compression test. But it tells you leak values of your valves.
Just to clarify it just an intake leak test. A leakdown test is done by using a leakdown tool that installs in the spark plug holes, sort of similar to a compression test. But it tells you leak values of your valves.
its normal for idle to raise when you press the brake pedal, you create a vaccum leak when you depress the pedal because the brake booster is doing what its supposed to do. it should only raise slightly though and only briefly.
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