Engine Vibration at Idle Diagnosis Help

I've got a minor vibration at idle in my '03 Tacoma (5vz), that I've been chasing for a bit and I'm wondering what to check next.

Recently replaced motor and trans mounts, spark plug wires and coil packs all with OEM Toyota parts. Plugs were replaced last summer when I did valve adjustment job and valve cover gaskets. Cleaned MAF then, and again yesterday. Other than this very minor vibration (only detectable at idle) the truck runs perfect. I'm probably just too OCD to where it bugs me to begin with.

Could bad body mounts allow engine Vibration into the cab? I can feel the vibration in the armrest and the steering wheel. Any tips on what else to check will be much appreciated. TIA. Happy Friday all.

 

By any chance have you replaced your PCV valve? If it's stuck open, it can cause the engine to stumble at idle because it acts like a vacuum leak. You can test it by disconnecting the hose at the throttle body side and plug it with your finger. Then have someone start it to see if it goes away. If it does then the PCV is stuck open.

 

I did replace it as part of the valve cover gasket job last summer, but I'll try that test to ensure it's working properly nonetheless. I have several older vacuum lines that appear okay. Could minor vacuum leaks elsewhere also cause the vibration or stumble I might be sensing?

Also perhaps worth noting is that every blue moon I'll have a long start (like 5-6 seconds of cranking or more, never doesn't start though and it's only happened maybe 5 times in the past year), as if it's starving for fuel. Could it indicate a fuel pump (which is original to the truck) could maybe be on its way out and be a culprit for this "stumble" at idle?

 

Definitely change the vacuum lines

 

Roger, just ordered 10 ft each of 4, 6 & 8mm silicone vacuum line. Do any of the vacuum lines with all those particular bends in them (like the one from the PCV to the throttle body, or the one off the front of the brake booster) have to have those bends formed in them? Or can I use the generic silicone vacuum line to replace those as well?

 

I don't know about the other ones but the one for the PCV should not be silicone because it reacts to oil and swells. I would order the OE one. I tried different type of hoses to try and save money before the OE one and they all collapse under vacuum once the engine reaches operating temperature.

 

Do you think it's safe to assume all the harder, formed vacuum hoses would also do the same if replaced by silicone lines? I'm thinking they're that way from the factory for a reason right? Might just order all of those from McGeorge if that's the case

 

I don't believe those have high vacuum so you should be good. I replaced all the other ones with rubber vacuum hoses from NAPA with the only exception of the PCV.

 

Awesome, thank you sir for your help. I just ordered the PCV hose and the longer one that goes behind the intake plenum. Hopefully between those two and my 3-10ft sections of 4,6, & 8mm hose, I'll have enough to do all of my lines.

 

Ok so I replaced the PCV valve, PCV grommet and vacuum line from the PCV valve (to the throttle body) with all OEM parts. No change in slight vibration at idle. Then I replaced all the remaining vacuum lines with red silicone lines, still no luck.

Does anyone think fuel pump (or something else fuel related) may be my culprit for this very slight vibration at idle. Just to reiterate, my truck runs great otherwise.

For a second I thought maybe my body mounts being bad could be a culprit, but the same vibration I feel through my armrest and steering wheel can be felt with my hand on the intake plenum too (same rhythmic vibration). Pulled one plug (that's only about a year old, with ~6-7k miles on it) and it looked pretty normal. Sorry for the long winded update. The search for an answer continues onward.

 

Iac valve, i need to clean or change mine