Idle a bit low - Proactive Ignition coil replacement question

[PTPT2002]

My 2004 4runner V6 SR5 has 200k miles now. I had my HG replaced at 155K miles (back in 2013). Fast forward a few years later, my car would occasionally idle a bit low. Down to slightly below 800-650 rpm (which vibrates the truck a bit) and most other times are normal when idling. Putting the truck in neutral seems to help by bumping the RPM up a tiny bit.

Had one coil went bad and had that replaced along with all 6 spark plugs. Replaced 2 Catalytic converters a little before then. The occasional low idle still remains.

Question: Should I replace the other 5 ignition coil or should i wait until they fail before replacing. Not sure if the low idle is caused by another 'soon to be defective' coil.

Let me know if you guys had experienced this issue before.

 

[riceandpho]

when is the last time the throttle body and maf sensor clean?
try cleaning those up and have the batter disconnected for 30 mins at least.
then with everything put back together, start the truck, let it idle for 15-20 mins with no heater or a/c on. it can help reset the idle a bit, also resets all your radio settings so make sure you write everything down.

 

[PTPT2002]

I have cleaned the throttle body and MAF not too long ago. I have disconnected the battery over 15 minutes and reconnected it.

Looking at it again after the change, the RPM would drop closer to 500 rpm during idle (not all the time).

I have replaced the gas cap to rule out any possible leak from there.

A bit puzzling right now.

 

[riceandpho]

it can be the spark plugs, im not sure unless others chimed in.

always check the spark plug gap, even iridium can come out of spec.i have mines at .39 on my tool, it works fine for me. denso only too, others have good luck with ngk also. bosch is bad for our trucks i think, atleast thats what i read on the 3rd gen when i owned one, but i had a 2.7L. that was for the 3.4 v6

 

[Johns06yota]

Check the rubber vacuum and fuel lines under the hood for dry-rot. I found that those were causing evap issues as well as a very low idle around 400 at times. Now that those are replaced it runs much better

My 2004 4runner V6 SR5 has 200k miles now. I had my HG replaced at 155K miles (back in 2013). Fast forward a few years later, my car would occasionally idle a bit low. Down to slightly below 800-650 rpm (which vibrates the truck a bit) and most other times are normal when idling. Putting the truck in neutral seems to help by bumping the RPM up a tiny bit.

Had one coil went bad and had that replaced along with all 6 spark plugs. Replaced 2 Catalytic converters a little before then. The occasional low idle still remains.

Question: Should I replace the other 5 ignition coil or should i wait until they fail before replacing. Not sure if the low idle is caused by another 'soon to be defective' coil.

Let me know if you guys had experienced this issue before.

 

[PTPT2002]

Good point. Where do you buy these vaccum lines assuming that they are bad? I just noticed one of the water line (by the clamp) is leaking a tiny bit of coolant right in front of the engine. Had a couple of P0442 and P0456 codes popped up which forced me to replace a gas cap.

I will check to see where else air is leaking from the engine. Hard part is the the low idle is not consistent (only occurs sometimes).

The truck had the same low idle symptoms even before the spark plugs were replaced. Denso plugs seem to be pretty good.

Check the rubber vacuum and fuel lines under the hood for dry-rot. I found that those were causing evap issues as well as a very low idle around 400 at times. Now that those are replaced it runs much better

 

[Johns06yota]

I ended up buying rubber fuel line from advance auto for everything. I can't remember the size I believe it was 5/16 but I'm not completely sure (you can tell if you bring the hose into the auto-parts store). The ones on the car were pre-bent but the line I used worked just fine. I payed 2 dollars per 2 feet of hose so in total I used about 6 feet roughly. I also had an intermittend rough idle and had replaced the gas cap to no avail. So far this has solved both issues and it seems to move through the gears more easily now. Hope that helps!

Good point. Where do you buy these vaccum lines assuming that they are bad? I just noticed one of the water line (by the clamp) is leaking a tiny bit of coolant right in front of the engine. Had a couple of P0442 and P0456 codes popped up which forced me to replace a gas cap.

I will check to see where else air is leaking from the engine. Hard part is the the low idle is not consistent (only occurs sometimes).

The truck had the same low idle symptoms even before the spark plugs were replaced. Denso plugs seem to be pretty good.

 

[waypoint]

These coil-on-plug ignition coils are very binary in performance, in my experience. They either work, or they don't. I haven't seen any cases of performance degradation as measured by either engine behavior or coil winding resistance...they run at nominal performance until they fail. So if they're firing, I'd leave them in place.

In terms of your low idle: usually a vacuum leak, next likely cause is one or more cylinders losing compression e.g. burned exhaust valve.

Whip out your vacuum gauge and get a reading on a fitting behind the throttle body at hot idle. Also observe for the vac gauge needle fluctuating at all, should be rock steady. Fluctuating = cylinder losing compression.

If vacuum reading is steady and normal (post your indicated reading, do some searching for normal values), I'd remove and clean the throttle body including idle air passage(s). Not sure if your vehicle has an Idle Air Control motor or if it's drive-by-wire. If it has an IAC, remove it from the throttle body and clean the conical valve and air passages thoroughly. New throttle body gasket is mandatory, don't reuse your old one. Torque the bolts to spec torque in an X pattern incrementally.