Hi Davesmopar! TPS at idle is 15.3%
No.
I think the jittery vacuum gauge needle displays a valve problem. Have you put in the known correct oil? If that makes no diff after some miles, I would wonder if the timing chain is stretched or has too much play.
With the engine at idle, the continued fluctuation of 1 to 2 inches may indicate an ignition problem. You should check things like spark-plug gap, primary ignition circuit, high-tension cables, distributor cap or ignition coil. Fluctuations of 3 to 4 inches may point to sticking valves.
Tester
If it is an ignition problem, one thing to check is whether the spark plugs are the exact ones Toyota specifies, and, yes, the correct gap.
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Good point.
Some folks think they can “improve” the engine performance with more expensive spark plugs. In my experience, that usually only leads to weird engine performance issues. Since you bought the truck used, there’s no telling what a previous owner put in it.
+1 for changing the spark plugs to OEM or equivalent.
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If it seems to bog down, go unusually slow, in those situations, could be a problem with the fuel pump, fuel filter, engine air filter, cat-converter. i.e. anything affecting engine’s ability to quickly move air & fuel into cylinders, and exhaust gases from cylinders to tail-pipe. Discount this idea if several known-good Tacoma’s behaved the same way during your test drives. The terms “go slow” and “bog down” mean different things to different people.
If your experiments show the problem is only or mostly at idle, you might want to ask your shop to check the ignition timing variation, advance/retard deviation from spark to spark, easily observed using timing light aimed at crankshaft pulley. Some variation is normal b/c the computer probably dithers the timing to improve performance & mpg. However, on my Corolla 4afe engine anyway, the computer doesn’t dither the timing when the engine is put in test mode. If your Tacoma is the same, ask shop to verify there’s no advance/retard spark dither in test mode. You might also check if the symptoms disappear then as well, would be an important clue.
Perhaps already mentioned, but loose/worn engine/transmission mounts could possibly cause this symptom.
Thank you Tester!! Any tips on how to test the coils when I change the spark plugs? I have a multimeter but don’t know what to check for in this case.
Roger that, I got the OEM Densos. I will measure the gap before I put them in and make sure it’s within the recommendations.
I really appreciate it George_San_Jose1. Yeah I think overall it doesn’t feel like it’s bogging abnormally during those situations. It’s definitely at idle. I checked the OBD timing advance during idle and it was 5-15 degrees, which is within spec per my manual.
That’s very interesting about putting it in test mode! I assume that’s what the manual is talking about when it says the timing should be only 3-7 degrees when TC and GC (terminals on the OBD plug) are connected? I will try that and see if it has any effect on the vibration.
I really appreciate everyone’s input thus far. You guys rock. This weekend when it warms up here in NY I will do spark plugs and compression test and change the oil if the plugs don’t fix it. I will also try taking off the serpentine belt for a minute to see if that makes the shake disappear. I will report back. If anyone knows how to test the coils with a multimeter, please let me know!
On your engine, is the fan connected to the water pump shaft?
The watoer pump bearing might be bad. Though if not loosing coolant, more likely the fan clutch.
Yes the fan is connected to the water pump! Not loosing any coolant. Here is the video of the guy who found a lot of play in his fan clutch and said it was the cause of his idle vibration. I am eager to test this. When I play with the fan on the vehicle, it doesn’t have this much play, but I can feel a slight bit. And I guess if i see it wobbling, that means there is play and something rotating off-center, right?
A wobbling fan will not cause, and will not result from, whatever internal engine dynamics are displayed in the jittery vacuum reading.
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Yes I was thinking that too…it can’t explain the wobbly needle. But it would be great if it made the vibration go away!
I think you’re suggesting it’s more likely the vibration is caused by whatever is causing the needle to fluctuate, correct?
Yes, and it has to do with engine vacuum. What could create regular and small vacuum jitters? Valves come to mind. Maybe EGR or some other system that is connected to engine vacuum?
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That seems a little high and is a good indication of a dirty throttle body and blade… A normal average TPS% in closed loop is 5-10%… I would replace the spark plugs (as mentioned by others) with OEM plugs and do a complete FST (fuel system cleaning) The FST will look like a IV drip running to a vacuum port, the throttle get cleaned manually and a cleaner goes in the fuel tank… Firestone does them for example…
If you have any movement in the water pump and or fan clutch that needs to be replaced, a fan clutch lets go and it can take out the radiator… If the outer bearing is worn out that does not mean that the inner seal is leaking… Coolant does not lube the bearings… lol
The inner seal goes bad and the water pump leaks from the weep hole, that is a warning that the pump seals are about to fail… but the bearings can just go bad with no leak…
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Can’t speak to Tacoma, but that’s definitely the case w/my Ford truck. Any play at all when attempting to move the fan blades horizontally or vertically, means water pump is soon to fail. I sometimes notice a little play on a good water pump when applying a rocking motion to the fan blades, but I think that is caused by the blades acting like a spring & bending slightly.
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That goes for the fan clutch also as stated…
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Thank you Shanonia, Davesmopar, and Georege_San_Jose for your input!! I really appreciate it.
Update: Today I replaced the spark plugs. I didn’t have time to do a compression test before the weather got bad (I am a streetside wrencher). The plugs didn’t fix the problem unfortunately. It does idle a bit smoother overall and today the vibrations at idle in P and N were minimal. But when stopped in D with the brake applied it was just as bad as ever. Also, the vacuum needle is still fluctuating rapidly.
Here is a pic:
The throttle body was recently cleaned when I brought it to a shop and it looks like they did a great job.
What do you all think about the plugs? Are some a little lean? I turned plug 3 over in the second pic because one side of its insulator is very white and one side is slightly browned.
One peculiar thing about this problem (see youtube video link below): It shakes in D when stopped with the brake pedal depressed. But if I am stopped in D using the parking brake on WITHOUT the brake pedal, it is much less vibration and it doesn’t feel like it’s going to explode. Maybe it’s just because the rpm drops when the pedal gets pressed? I don’t know if this is normal or not?
I have wondered if there is excess air coming in through some part of the brake booster when I push the brake pedal causing a vacuum leak in this state. The pedal does feel squishy / easy to press despite new brake pads and (as far as I know) good fluid. And when I run the engine then turn it off and remove the vacuum hose from the booster, I don’t hear any air escape from the booster. I tried hooking the vacuum gauge up to the booster itself with the truck off to see if it holds vacuum and it didn’t, but I don’t know if that’s a valid test. I can’t figure out if any of this is significant or not. Is there a test to see if it’s the booster for sure?
I did remove the electrical connectors for the brake lights to see if any difference (maybe an electrical problem in that state) but no change.
Next is the oil change, maybe tomorrow if I have time. Thanks again for following along and please let me know what you think!
There’s a little variation in deposits seen from plug to plug. But I’m guessing that’s normal, just a cylinder position effect. Doesn’t seem likely the idle shaking is a spark plug problem.
I guessing that’s an important clue. Plus the fact that the booster doesn’t hold vacuum. One experiment you could ask your shop to try, does removing the power brake booster from the equation eliminate the idle shaking (in D and brake applied)?
The link below is a little on the long-winded side, but has some pertinent info.
Test 4: A Test to Do if Your Engine Misfires When You Depress the Brake Pedal
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