Engine noises…

I have been noticing that after my truck has been running at a high speed (50mph+) for longer than an hour, when I slow down to come to a complete stop the engine starts to rumble abnormally. I can accelerate and it goes back to normal.

I can be running it for hours at various speeds and everything is fine. But only when at a high speed for an extended period of time this occurs.
Has anyone had this happen?
ANY advice is appreciated!
-voodoo

 

Curious, can you get us a picture of your throttle body opening? Like, pop the intake tube off and shoot us a picture of what it looks like, before attempting to clean it. (Can give cleaning tips and what to avoid if you want ... just don't slam the butterfly shut, and never spray anything into it. Sorry if you know this, we've seen some ppl screw themselves on here)

 

Check what shifty said first. He's the man with 1GT.

At steady state throttle and RPM, your ECM is shooting for a specific ignition timing and fuel map. If you have parameters pulled up your stock engine ECM will shoot for a 14.6AFR with around 15-20* ignition advance.

I say that because you haven't mentioned if you're up to date on tune-up parts. Old up-stream O2 sensors can read off of actual value, even if they aren't throwing codes. And old spark plugs can be fouled or not throwing as hot a spark.

At long-term steady state driving if your air/fuel ratio is off you could be running extended periods of a rich or lean condition but your ECM is reading it as fine. You come to a complete stop and your engine stumbles trying to reconcile the incorrect AFR reading or spark timing with what your engine is actually doing. You bump the throttle a couple times to force the ECM to react to the changing condition and move to a different portion of the fuel/spark map thus resolving the stumble.

I may be thinking too far into this, but when was the last time you changed plugs, upstream O2, cleaned throttle body, cleaned MAF, checked for vacuum leaks, changed air filer? But the problem could be as simple as a gummed up throttle body.

 

@shifty` @Riverdale21
Im still a greenhorn when it comes to any work under the hood.
Changed my spark plugs early December of 2023. 2x checked the plugs and they are gapped perfectly.
Will update y’all this weekend when I can get to everything else. Thank you!!!

 

It's your fuel map. It's got a nasty hole. That's why you're unloading in third. I'd lengthen the injector pulse another millisec, and just tune the NOS timer, you'll run nines

All jokes aside, I would agree to start with the TB cleaning. Disconnect the negative terminal on the battery and leave it off for 10 minutes to clear out all stored/learned behavior in the ECM. While you are waiting, clean the TB. See how she responds after that.

 

But it's OK to run SeaFoam top engine spray through the throttle body, correct? Or is there a better way to get the seafoam in there?

 

Brake booster vacuum line works too. Just don’t over spray or fill with liquid seafoam, can cause stalling and even hydrolock in extreme examples.

 

I just did a top-end treatment thru the TB a few days ago: https://www.tundras.com/threads/wha...-gen-tundra-today.2558/page-1956#post-3556930

Seafoam explicitly warns against using vacuum lines to apply it. I'd be lying if I said I haven't done it a dozen times or two, but if the manuf'er recommends against, there must be a reason...

 

Thanks, guys. Does one way distribute it throughout the system better?

Also, I hope you all will chime in on future posts. My steering and suspension is a hot mess. I'm not particularly mechanical and could use some good advice. First up is a VCG-SPT-PCV valve replacement (Parts in hand) and codes indicating EVAP gross & minor leaks (possible TSB fuel filler tube issue-replacement) along with upstream O2 Bank 2 sensor (delivery today). Got pics to upload and view. Trying to get the engine square before VCG and steering-suspension work.

Also, LBJ, OTR, ITR, Boot replacement. Soon enough, the steering rack will need replacement but trying to limp along til I can get all parts in hand.

 

That should be less important than what the manufacturer advises you to do and/or not do.

Ok, and you're aware of the parts where you really need to use Denso (or other OEM brands), right? Not just limited to OEM LBJ and fresh OEM LBJ bolts. Denso on O2 sensors. PCV doesn't matter. O2 you really want to replace in pairs, per bank (upstream/downstream at same time with Denso brand sensors. Note 2WD and 4WD sometimes use different sensor part numbers, I always advise picking the 'exact fit' part at www.densoautoparts.com

On the EVAP, do yourself a favor: Smoke test using the supplied smoke test port under the hood. ASAP. Do it before you take up the parts cannon, seriously. Verify your vacuum hoses, smash to check for cracks/splits, cut the last 1/2" off and re-seat the hoses. EVAP relies on having a sealed system between the tank and manifold (and return). While your year, IIRC, is actually prone to the TSB on filler neck failure/crack (run your VIN against the TSB's "VINs affected range"), it's worthwhile to check other things; it should only throw a small leak, I think (the TSB says for sure).

 

My evap gross and minor leak codes were solved by a new gas cap. If you tighten it and it's still loose when you open it, it's not sealing anymore.

 

My MIL's gross/minor EVAP codes on her new-to-her Lexus were solved by telling her, "Woman, you NEED to tighten the gas cap until you feel 1-2 clicks!"

She honestly had no idea it was necessary to have the gas cap tight so it could act as the EFI pressure valve it was intended.