Bad idle/accel after spark plug change

Hey, I’m probably asking a question that has been asked before.

I decided to change my spark plugs on my 2000 V8 4.7 because the idle was pretty rough and I figured I’d start there to see if it helped. Replaced with OEM plugs, gapped at .031 per the manual. After the change, the idle is more even but REALLY low RPM, and my accelerator is practically useless.

I know there are a number of other things that could be contributing to the original problem, including my coils or the vacuum system, etc. But does anyone have any suggestions about what to try next in order to even get the vehicle back up to drivable? I did do the “idle relearn“ that I’ve seen for Toyotas, where I turn the ignition off and on a couple times and then let it idle and drive for 5 to 10 minutes. But it didn’t seem to help.

Any advice is appreciated, thanks.

 

Did you torque the plugs down? Gases can pass by the plugs and cause misfire. If you did, I would guess more likely you have cracked coils that are shorting out and causing misfire. Unplug your coils one by one while idling and look for a change in idle speed. And mist the area with water in a spray bottle, check for arcing.

 

Thank you, I can give that a shot and see what happens.

When I took out the old plugs they were gapped larger than .031. I’m tempted to just try and put them back in, because at least I could drive before attempting this repair.

 

During any of this rough idling, there has not been a trouble code recorded "Check Engine" light ?
What actual RPM number are you seeing when it's "REALLY low" ?
At anytime during this maintenance did you unhook the battery ?
As for accelerator, explain please.

 

Clean TB, perform idle relearn again. Make sure everything you took off to do plugs is back where it should be and in good condition.

 

Thanks all for chiming in. I’m admittedly new at trying repairs myself. Appreciate the wisdom of the crowd.

Didn’t notice anything when I unplugged individual coils. After running it a bit more tonight, RPM’s are now around 500 when idling in drive (before was barely 250, seemed really low to me).

Bubba, for the accelerator issue, it is just not responsive after the change. I have to practically floor it to get the vehicle moving and then it jerks to life. Almost backed into my house! I saw some comments in other threads about APP sensor or resetting the accel pedal position (by depressing five times with key turned to on). Not sure if this issue is related to spark plug change or if I just bumped another wire or something.

I did disconnect battery before changing plugs.

I had a Check Engine light for 02 sensor which I recently had addressed.


THinTx, I had wondered about the throttle body, so that will be a next step too. Seems like a relatively easy process.

 

500 rpm idle is normal after warm up IMHO but not 250.

The ECU will now be relearning after spark plug change. I would recommend doing the MAF sensor and Throttle Body cleaning as others suggested as soon as feasible. Plenty of utubes on cleaning either one and suggest CRC MAF(mass airflow) and CRC Throttle body cleaner which you can get at AZ, Napa, Wallace wurld etc. I would also suggest to unplug battery while doing the cleaning and then the ECU can go thru a relearn process after that

Hmmm, perhaps after cleaning MAF/TB and other suggested periodic maintenance, it'll help with that issue but circle back and let us know how it goes.. Sounds like your beast just needs a little TLC

 

Did you get pre gapped or gap them yourself? The last ones I put in my wifes camry were supposed to be pre gapped iridium and after the install it ran rough. Took them out and checked the gaps and they were close but not spot on. regapped to spec and its been fine.

 

Hey again. Thanks for the tips. I will put some attention into the MAF and TB this weekend and see how that might impact things.

Cory, to your question, I gapped the plugs myself because they were all smaller than the .031 I saw specced for this vehicle. The ones I pulled out were actually bigger, so perhaps that's why I'm seeing some changes. Hopefully some of this other cleaning and an ECU relearn will help it get all in sync with itself again.

I'll let you know how it goes. Appreciate the help gang.

 

Did you get the plugs from a reputable source? There are fakes on Amazon and eBay that cause issues

 

Good point. I almost destroyed our Rav4 with counterfeit Denso plugs


https://www.tundras.com/threads/counterfeit-denso-spark-plugs.64225/

 

I would recommend checking your coils to see if there are fine cracks in the tube part.

 

Hey all, here's an update.

• Spark plugs were (as far as I can tell) Densos in the OEM box. The idle does actually seem better now overall, so perhaps the plug switch has helped the initial issue of the rough and lopey idle. Still starts a bit weak (stalled a few times) and shifts roughly compared to before, but I'm hopeful some more driving might help even things - if only I could drive it! Someone mentioned coils, they all look pretty good. I may replace one that was starting to show some tiny cracks in the boot at the end.
• Cleaned MAF sensor and TB with CRC. TB wasn't too nasty, but I did get some gunk out of there.
• This new issue with the accelerator is the persistent problem. It showed up after the spark plug change. Maybe I bumped some of the old brittle wires on throttle positions sensors during the work, or resetting the ECU brought this up, or it's just coincidental timing. I'm getting codes P1120 and P1121, which are for the APPS. That matches my experience: after starting, it will drive normally for a moment and then go into limp mode. I can drive really slowly, but only get throttle response when I push the pedal pretty far, and then it jumps. I'm reading that if these codes are present, the ECU will force limp mode. It's a tease because I'll start it up and drive away, and it feels good, and then womp womp, limp mode... then I have the drive of shame around my block at 10 mph.
• I'm thinking I'll check the wiring first to see if there's anything obvious, and then I may look into the part and repair. Would love to fix it myself, but I might be getting in over my head.

Thanks.

 

Where did you get the plugs from?

Denso's on Amazon (and eBay) are harder to get legitimate ones. Tons of fakes mixed in with real ones in the warehouse...

 

A lot of times the tube part of the coil is what cracks. I wouldn't be surprised if that's what's causing your beef, but ... it's a lotta money to throw willy nilly at something. If your truck is over 200k, may be worth dropping the coin if you can spare it.

 

Pics of coil cracks:

https://www.tundras.com/threads/cracked-coil-plugs.56983/

But look closely at this post, I know it shows one of the same images, but look at the 2nd image. You may need 'zoomers' on to be able to check for hairline fractures.

https://www.tundras.com/threads/wha...t-gen-tundra-today.2558/page-373#post-1474236

 

shifty, you think the new accelerator issue and codes could be related to the coils? That would make a bit more sense to me because I actually messed with those during the plug switch (vs these other sensors which seemed to be fine prior). Though I know it’s all connected.

I have about 175K on the beast. Changing coils is something I know I can do, so maybe I could start there before the sensors to see if my pedal comes back to life?

 

Oh and, assassin, I did get the spark plugs on eBay. Checked past reviews for parts and seller first, but I know that’s not a 100% promise of quality. The engine def runs smoother since the change if that’s any sign... though I do have these new issues, so I don’t know what’s related.

What online parts source would you recommend?

Thanks all.

 

Did you put the old plugs back in, and go back to the original parts to see if anything changed?

 

This. First thing I would have done.

I guessing there is a bad plug or two in the mix, high resistance, causing this.

If you have an multimeter you can check them, should be between 5 and 10k resistance.

And while doing this check coils very closely, might have cracked one or two with that many miles on the OE ones.

 

Rock auto.

Or go to the local parts store.


I got 2 sets of fake Denso plugs from ebay before giving up.

 

Ah okay, maybe I got some lemon plugs too. Low stakes to purchase some from Advance and try them, I suppose.

Funny, you’ll see in the thread above I actually dabbled with the idea of putting the old ones back in, but then I didn’t... learning a lot here.

Thanks!

 

Get some good pics and I could probably tell.


Here were my ebay sets vs real.

1st fake (fake on left, real on right)


2nd fake (same)

 

This is critical, I would address this before going down any rabbit holes. I also received fake plugs, in a denso box, from a highly reputable Toyota parts seller on Ebay. Amazon and Ebay are pretty much off my shopping list these days for critical parts. They counterfeit everything. If you're new to maintenance, I would suggest a wire style gapper instead of the ramped coin style they sell at the auto parts counter.

 

Amazon and Ebay have become so terrible about this. I can't even buy a tool off of Amazon anymore

 

This has been my experience too. I won't buy auto parts from either anymore. I've had good luck with Rock Auto.

 

Hey all. I picked up new Densos from AAP and switched them out last night. The first set looks pretty convincing, but who knows, maybe they were knock offs. I’ll avoid eBay and Amazon as a rule. Either way, I have some real ones in there now.

Unfortunately I’m not seeing much change in the pedal issue. Overall the idol is better, like it was with the first set of plugs, but I’m getting no response with the accelerator. Stuck in limp mode. So perhaps it’s back to exploring the APP sensor. I might need to seek a mechanic’s look at this point.

 

Any codes pending?

Don't the earlier trucks have a throttle cable and tps? Check the hoses and intake tube, look at maf/tps connector and wires. Also worth checking to see if maybe the maf or tps is bad.

 

My 01 has a throttle cable, but it seems that it electronically actuated anyway.

 

P1120 still coming up (APP sensor).

This model year has drive by wire, using the physical cable to provide input for the PCM to move to throttle plate.