weird acceleration, a little concerned

I was going out to dinner last night and on the way back the truck felt a little sluggish, especially in second gear. I was with some friends though and didn't pay much attention to it at the time. Tonight I go to the gas station and notice it again, so I ran it up to about 3000 rpm during acceleration and all of a sudden it went from sluggish to perfectly normal, like I floored it but I hadn't. Only thing I've done before I noticed it was change the oil, grease zerks and wash out the engine bay this weekend, but oil level is fine (5.5 quarts 5w30). Only thing I can think of off the top of my head is maybe some electronics got wet while I was washing it out, but that was 2 days ago.

Did some searching, but nothing similar comes up. Got a 6spd v6. It got too dark to do much checking around once I got back, but any thoughts would be appreciated before I get out there in some daylight to check it more thoroughly.

 

subbed - i have the same issue but only when my engine is cold...

 

Any check engine light?

 

No check engine light.

 

same issue with a cold start too.

 

Well if it's just a cold engine thing I guess I'll just have to get used to it. Seems odd that it just started up out of the blue though.

 

any smells (rich fuel burn), black smoke?
Just runs rough at lower rpm's?

 

there use to be a reflash for your ecm on 05 to 07 taco's for this concern on cold start...not sure if the newer yrs still have this flash....i have since left working toyota....if its only on cold starts and soon as u hit warm up i would not worry at all.....

 

Subbed. My truck does the same.

I have noticed that it's repeatable. If it's driven conservatively for a length of time (and it doesn't seem to matter that the truck gets shut off and restarted for this) it will start adding a small amount of ignition timing across the board. If I didn't have the ultragauge on ign advance I'd never see it, it's only about 2-3 degrees. When it gets a high load situation for the first time after it's done this to the timing tables it does the cough-cough-GO GO GADGET HOTROD syndrome you were describing.

In defense of toyota the ignition advance change makes a fairly substantial difference in mileage. I've seen as much as 4 MPG difference at cruising speed between the two "behaviors". FWIW it takes about 15 consecutive minutes of purely conservative driving to get the ignition timing up there.

I conjecture that it may be switching between ignition maps for regular and premium fuel, as only high load on regular fuel would knock it down like that. I haven't put in a tank of premium to test this yet, but as I'm down to 7 gal left in the tank, I suppose I could put a couple tanks through to monitor behavior.

***

Before I forget... during that time it hesitates, I've seen ign advance drop so far it landed at 6 degrees after TDC. If it's just doing the sluggish acceleration thing the advance is sticking between 6 and 10 BTDC. Normally it likes to stay between 15 and 20 degrees advance at 80-90% load situations and it will go back here with regular fuel, which would conflict with my fuel type hypothesis. Back to the drawing table.

Temperature is not always a factor either. That time I saw 6 ATDC it had been running for nearly two hours.

Ninja edit: another idea is that it may be wanting to keep the cams retarded for improved mileage and the transition when they advance up isn't as smooth as it should be.

 

I did some driving tonight and it definitely appears to be a cold engine thing, although the engine still seems to be under more load than normal. I may just be over analyzing now.

No, nothing you can tell without driving it.

Good info, I'll definitely check into that when I get in the vicinity of the dealer.

I don't have anything to measure all this, but it does seem to make a lot of sense. However, I definitely haven't seen any better mpg at any point with this truck. I'm usually between 15 and 16 mpg, so far on this tank it looks like I'm around 14 or 15, but I also do short distance drives pretty heavy on the gas, so nothing unusual. I also use 93 octane, so from this experience I don't think it will correct the problem using different fuel grades.

 

I did have cold issues in my Honda Fit. It wouldn't allow 16 valve operation under 125 degrees F water temp, and it was really doggy with just 12 valves to breathe through; usually I'd be accelerating (generating heat) and it would hit 125F and just take off like hotcakes - well, as much as 91 cubic inches can.

The purpose of that was to prevent oil pressure fluctuations when the VTEC solenoid would cycle; that's why every honda stays out of hot cam lobe operation when cold. Even though oil pressure is highest when cold, flow is lowest, and if there's flow diverted in the head there is the small chance of a bearing starving somewhere if the oil is thick enough.

It is possible Toyota designed a similar safeguard into their VVT-i cam phasing. As far as I know those adjustable cam gears on the intake sticks are adjusted with oil pressure like most every other automaker's. If it is that it would be harder to pin down the temperature threshold, after all it's not just saying TA-DA! and bringing 4 extra intake valves into the mix like my old car.

Still, doesn't explain that weird late spark like I had. I'm starting to wonder if I had some poor quality fuel that week.