Rough idle: scanner clues?

supton · Mar 23, 2016

I've noticed a bit of a rough idle the last couple of days, warm/hot idle in gear on my automatic transmission Tundra. Doesn't seem there out of gear (higher idle). At 120k I'm due for plugs, so I plan to order a set and swap in at some point in the next couple of weeks. Just have to order a set. In the meantime... is there anything that can be checked via either my Scanguage or my Techstream copy to indicate worn plugs? I'm guessing worn plugs would need higher voltage, but I don't know if timing advances so as to counteract a delay in firing, thus giving a tell-tale sign of old plugs.

I don't have a miss, certainly no CEL, but something just feels off. Am curious what can be scanned for.

HerrStig · Mar 23, 2016

Worn plugs will eventually give you a missfire code when the crank sensor detects an drop in idle speed.

LeakySeals · Mar 23, 2016

I just changed the original Iridium plugs on my Escalade w/130k and a similar random shaky when warm issue. All 8 plugs looked beautiful, not very fouled. The gap was good. The idle difference was amazing. The engine idles just a little bit higher which makes all the difference. Next in line is a new throttle body with a built in TPS to (hopefully) resolve a very occasional low idle vibration. And I don't like the sound of the AC compressor when it kicks in. Maybe something going on there dragging the engine down.

supton · Mar 23, 2016

Hmm, looks like I can get Denso's at Advanced for about the same as online. Have to run out today, maybe I'll order online and swap out sometime this week (instead of in a couple of weeks).

LeakySeals · Mar 23, 2016

For whatever reason RockAuto is the cheapest place for plugs including shipping. I use NGK but I think the Denso's are also cheaper there. If you can get them locally for under $10 that's great

supton · Mar 23, 2016

$9/each minus 20% if I order online through AAP, so $7.19/each (no tax). I'll go that route.

86cutlass307 · Mar 23, 2016

When you replace the plugs, clean the throttle body thoroughly, reset your ECM to allow it to relearn the readiness monitor(s) parameters, if your software allows you to watch your O2 sensors working in real time, watch them for a while. Some people like to run them till a code pops up. Usually around 90K - 120K they should be changed because they do get contaminated/lazy and have a big effect on drivability. If you swap the sensors out at a different time, be sure to reset the ECM. My Tacoma V6 recommends every 30K change for the plugs for emission purposes. The plugs I have pulled out are usually used up by that time; it uses copper based plugs though.

supton · Mar 23, 2016

I don't have the ability to do O2 sensors live. Thought about getting a scanner but never got around to it (my Techstream is on a laptop that lacks a battery). Project for later I think, O2 sensors (quick look shows they are $90 a pop, and since I have four I think I'll approach with caution).

LeakySeals · Mar 23, 2016

Hey that's an awesome deal! I wonder what you can find out about the O2 sensors by pulling the plugs. Would think if the O2 sensor is getting lazy your plugs would be sooted with unburnt fuel and you would notice a lack of MPG. Only the two in front of the catalyst are involved with the ECU fuel air mix. The other two behind the catalyst are just comparing the results behind the catalyst AKA P0420 P0430 catalyst efficiency codes

LeakySeals · Mar 23, 2016

Also living in NH you're going to have one [censored] of a time getting those O2 sensors out. So if you think about pulling one out be prepared to replace it.

supton · Mar 23, 2016

Yeah, I'm reluctant to do the barest minimum until I have a vehicle which I can use to run for parts (the other vehicle cannot be counted on as wifey has a busy life!). MPG has been poor as of late, but I've been driving kinda fast lately (70mph) and it's been chilly; hanging out around 18mpg. So I don't think the O2's are done just yet.

I haven't read up yet on how Toyota did this vehicle. I thought, at least on some vehicle somewhere, that the front sensor was wideband and the rear sensor is narrow band; and as such, the rear sensor is used to calibrate the front sensor. The rear sensor is of course used to monitor catalyst efficiency but manufacturer dependent the front sensor is... I dunno, I simply haven't read up on it. I'm not sure if wideband sensors wear like narrow band, etc.

Thus it's a project for some other time. Preferably during the summer.

LeakySeals · Mar 23, 2016

One more I forgot to mention.. fuel injectors. They get dirty. A fuel system cleaner with PEA is beneficial. That was the ruff idle problem in the old Camry in my signature

another Todd · Mar 23, 2016

Vacuum leak, from a degraded or loose vacuum hose. Or Dirty injectors (previously mentioned). I doubt it's the plugs unless it's an oil burner.

The Critic · Mar 24, 2016

Did you recently replace a battery on the Tundra?

supton · Mar 24, 2016

Nope, same battery as from three years ago. It got warmer, so I figured I'd let it go throught the summer.

punisher · Mar 24, 2016

Originally Posted By: another Todd
Vacuum leak, from a degraded or loose vacuum hose. Or Dirty injectors (previously mentioned). I doubt it's the plugs unless it's an oil burner.

On the mark.

Look for lean trims at idle (trending to normal trims under load) to confirm a vac leak. Injectors, dirty injectors, with bad spray patterns cause idle roughness. All too common back in the 80s when injectors tended to form deposits more often.

Superflop · Mar 25, 2016

Originally Posted By: supton
Yeah, I'm reluctant to do the barest minimum until I have a vehicle which I can use to run for parts (the other vehicle cannot be counted on as wifey has a busy life!). MPG has been poor as of late, but I've been driving kinda fast lately (70mph) and it's been chilly; hanging out around 18mpg. So I don't think the O2's are done just yet.

I haven't read up yet on how Toyota did this vehicle. I thought, at least on some vehicle somewhere, that the front sensor was wideband and the rear sensor is narrow band; and as such, the rear sensor is used to calibrate the front sensor. The rear sensor is of course used to monitor catalyst efficiency but manufacturer dependent the front sensor is... I dunno, I simply haven't read up on it. I'm not sure if wideband sensors wear like narrow band, etc.

Thus it's a project for some other time. Preferably during the summer.

front (upstream) sensors Monitor A/F ratios and are all you need to change for drivability. Rear sensors monitor catalyst efficiency and only really need to be changed when a code for is thrown. Clean throttle body and maf sensor as wl as check air filter when doing plugs

supton · Mar 27, 2016

Ran the fuel tank low, put in Gumout Regane and filled up. Probably placebo effect, but I swear 9 miles later it seemed better.

Pulled throttle body today; of course didn't take enough pics. This was the backside:

After cleaning:

Pulled plugs, other than #5 seemingly swimming in oil they looked... worn. All seemed to have oil on the threads but Might run this set for a short period of time (120k, which is OEM rating). Replaced with Denso's, will see tomorrow how it runs at hot idle.

I can't find my spark plug gap tool but they can't be that far from the stock 0.044", a quick quick check with a 0.04" feeler did not indicate "huge" gap left.

supton · Mar 28, 2016

Idle seems better. In gear it was barely 600rpm and now it's like 900rpm! I should double check stuff as it seemed off--doesn't engine brake like it used, wants to roll forward at a light much more aggressively, all like it's simply idling too high now.

hypervish · Mar 28, 2016

Did you pull the battery cables to reset the ECU after cleaning the throttle body? That would explain why it's idling high. ECU needs time to re-learn. It will do it quicker if you disconnect the battery for a bit, and have it start over versus learning over what it already has.

Rough idle: scanner clues?

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