So I have a Toyota Yaris 2010 1.3, I have had it for about 5 weeks and it’s second hand. From day one I noticed that the car will idle at low RPM (around 500 rpm) it’s quite jerky and shaky, but nothing overly excessive, and it would occasionally cut out but it hasn’t done that lately. I took it to a mechanic who identified two error codes to do with the throttle actuator system. I took it back to the dealership who advised they replaced the throttle, there are currently no warning lights or error codes, but the problem is still present. I feel like I’m shooting in the dark because I have already replaced the air filter, it hasn’t helped, I’m not sure what else I can get checked especially when there are no current error codes or warning lights. It’s also difficult to take it to a garage because they want to run a diagnostics on it which will make me out of pocket just for no error codes. Could it be the spark plugs? I’m completely new to using a Toyota, I previously had VWs, and it feels vastly different, took me a while to get used to it. I don’t want to make a mountain at of a molehill but it just doesn’t run as smoothly as I would hope.
You are shooting in the dark. But just throwing parts at the car will cost you more money than that diagnostic fee.
Even with no codes, a good mechanic can look at the various sensors to see what is going on. A 12 year old car, likely with 100,000+ miles on it (you don’t say), can have wear that affect the operation. You don’t have to use the dealer but you need a shop with a scan tool that can view all the systems in real time. If your regular mechanic referred you to the dealer for a throttle system replacement, I’d guess he doesn’t have that tool.
Thank you - it has 80k miles on it, I noticed the problem straight away and because it was under warranty I returned it to the dealership, my mechanic did have the required tools to check but I only took it to him 3 days after purchase so I didn’t want to void any warranty so I took it to the dealership for their mechanic to diagnose and carry out the repair work which resulted in a new throttle body, but it still runs the same
Take it back to the dealer until they fix it correctly. Get a written receipt for each visit. Is this a Toyota dealer or a used car dealer? I ask because a Toyota dealer, or any new car dealer with a used car lot, will be better equipped to handle your issue.
500 idle rpm is probably too low to allow the engine to ever run correctly , esp driving at slow speeds, stoplights, etc. My Corolla’s warm idle spec is 800 rpm, and it is very critical to proper engine operation it idles at exactly 800. Corolla is older than your Yaris, so idle speed set differently. But however it is set on your Yaris, that’s where your mechanic should be focusing their att’n imo, whatever it takes to get the engine to warm idle at the spec’d RPM. Replacing throttle body was a good guess, but seems there’s more to the problem than just that part.
So what’s causing it? Sure it could be the spark plugs, but it could be a lot of things. If I had that problem, after a basic tune-up (spark plugs, engine air filter, oil and filter change as applicable ), I’d be testing in roughly this order
Any stored diagnostic codes?
Throttle positioning system working ok?
Fuel/air mixture & fuel trim ok?
Crank position sensor working ok?
Fuel pressure ok?
Engine cylinder compression ok?
Sometimes it is possible to mickey-mouse a diagnosis & repair, make a guess and it works. But I doubt that will be effective in your case. Gonna have to bite the bullet and pay your shop to systematically go step by stop until it is fixed. On the upside, once the problem is fixed, engine running perfectly, you’ll have done enough to avoid some other potential problems as well.
when he changed the throttle body did he reset the pcm ? It needs to be reset if it wasnt . you could do it by pulling one of the battery cables for like 20 minutes .
Did a previous owner try to do some PCM tuning? The idle speed should be controlled by the PCM, by software. Could the PCM be faulty? Is there a fault code present that would prevent the PCM from controlling the electric throttle, such as bad position feedback?
Proper idle speed is 550 to 650 rpms, what you see is likely normal. New engine mounts might improve idle quality, but you may never be satisfied with the idle.
I would bet on a bad cam and/or crank shaft position sensor. They are easy to replace and not expensive (less than $20). I wouldn’t focus on the RPM…the rough idle and the car dying are what I would be complaining about and bringing in for the warranty fix.
I just went through this with my car…I did a super tune up due to all the parts being 20+ years old…I found 2 bad parts, the Cam sensor was cracked (causing intermittent stalls) and the fuel pressure regulator was faulty causing long cranks before the car started.
In addition, new plugs, wires, a starter and cleaning all sensors resulted in a 3mpg boost! Coming up on 21 years old, runs like new!
Automatic trans or manual? With A/C off, warm engine idle rpm spec looks to be 650 to 750 rpm for automatic; 550 to 650 for manual. Still 500? OP might try disconnecting battery for 5 minutes, then re-connect, might reset what needs to be reset. Suggest to first make sure before disconnecting battery there are no stored diagnostic codes, CEL is “off”, and turn everything off that isn’t required, shifter in N.
