Rough idle at cold start, check engine light flashing. Went away after restart

Went to cold start my '01 with 277k miles after about a week of not starting it. It ran terribly for about a minute and seemed like it was going to die at a certain point before I shut it off. The check engine light was flashing which means "DO NOT DRIVE" as far as I know.

However, when I started it about 5 minutes later, everything ran as it normally does and the check engine light was off.

This thing is due for a timing belt (87k miles, 10yrs) and always skips a beat before firing up (misfire?). I haven't been driving it waiting for my AISIN kit to come in. Checked fluids, oil was slightly lower than normal, coolant seemed fine; I just changed both 2k ago. No evidence of coolant over spray around the block. "Smoking" quite a bit but I chalk that up to condensation, being in the PNW and it being cold, didn't smell like anything but gas. Also I have a pretty big exhaust leak, its near the rear hanger so I feel like that's not the issue. Could the timing belt have slipped or something? I feel like I should be concerned but I'm not sure where to start since the issue resolved on it's own. Compression test?

 

What codes are logged? Flashing CEL is major problem like misfire etc. That info would immediately tell us why it’s bucking, yeah? Then we’d have something to speculate on…

Outside of that key info we don’t have but really need….

I’d check the timing belt condition first, knowing it breaking will brick the engine. Toyotas 9yr/90k time window is only valid if you use OEM parts, and some people don’t. Aftermarket may only last 5yr/50k miles.

Next I’d check the timing. I can link a website I always link to check. LMK. Rodents have been known to pack acorns and shit in the timing covers and one can cause the belt to jump a tooth or two. A failing tensioner or pulley could cause issues too.

Then I’d check the condition of the cam position sensor and its wiring at the driver side cam cover, as it can get misrouted and get cut by pulley or belt.

Then I’d check the crank position sensor and its wiring, since it often gets misrouted during timing belt change and gets cut thru by pulley or belt.

I’d be checking the power steering air control valve, due to mentioning the smoking at startup?

I’d also like to know what other maintenance was done recently: Did you do anything that had the battery unplugged more than 10-15 mins? Did you clean the throttle body and do something dumb like spray liquids directly into the throttle body?

 

I would take it as a condensation event, use some dry gas and possibly change your spark plugs as they’re probably fouled from running rich with the smell of unburned gas.

I experienced something similar after letting my truck sit for the weekend thorough a 3 day rainstorm fluctuating between light and heavy periods of rain.

For me it was changing the plugs, coils and using dry gas and then running it a mile or two and back on a country road to get it smooth running again. I may have gotten by without changing the coils as the dry gas and changing of plugs had the biggest effect.

 

@shifty` I'll have to go get a code reader. And the only other maintenance done recently is the center support bearing. However, the battery terminals are slightly corroded and loose-ish. I've had to wiggle them after a complete non-start (no dash lights, etc) a couple of times. Also, the air filter is trashed right now, have one on the way.

It bucks once right before firing up on every startup (been ignoring this out of fear that it's a major repair because it hasn't changed). The weird thing is that it ran totally normally on the second start, and third, etc. My thought is that the timing was off somehow, due to the cold and condition of the belt, jumped a tooth or something but settled. Like you said though, just speculation. I probably won't drive or do anything to it until I change the timing belt (with a much more knowledgeable buddy) and check everything then.

@Jack McCarthy This is interesting. I may as well do the plugs and coils, no idea when they were last done. I am hoping the jump/buck before starting up is caused by an ignition issue and not something major. Dry gas is something I haven't thought about using.

 

Low voltage/poor ground, or poor battery voltage will also cause bucking like this. And would be spotty between startups, variable behavior….

 

Good to know, really hope it's just that, I'll look into new contacts as well. I had a trusted Toyota shop take a look at it recently and they didn't mention anything about a misfire or odd codes, but it was bucking like this for sure when they inspected.

 

Only use OEM (Denso) for plugs/coils on your 01 otherwise you may open up a can of worms (if you replace them).

 

@shifty` I should have also mentioned that it only bucks on cold starts. Not when it's warm.

 

When you say "cold starts", is that after sitting for days, or could it also happen after sitting for hours, like you jumped into it in the morning and drove it to work and it happened, worked 6-10 hours, then jumped into it to drive home and it happened again? Or does it need to sit for a couple of days?

 

@shifty` After sitting for several hours, just when the engine is cold. However, I just sanded/cleaned and tightened the battery contacts and replaced the air filter, which was the worst one I've ever seen (rat probably, vehicle sat for 9mo at one point), and am now letting the engine cool. I'm going to see if it still bucks on startup in a few hours and see if the fact that it was probably starving for air is part of the rough idle problem.

 

If you found evidence of mice in the air filter box, you need to get some (specifically labeled) MAF cleaner and clean your MAF. It's quite possible you have tiny or even microscopic shreds of filter sitting on/coating the MAF's sensor.