Engine RPM bouncing up and down after cold start

[avensisnz]

Hey guys, I've got a 2013 Toyota Avensis with the 1.8 litre petrol engine and manual transmission. After a cold start, the engine idles normally, but after driving off, then shifting to neutral or depressing the clutch, the revs start bouncing up and down. It does this for 10-15 seconds, then idles normally from then on. Note: The air conditioning and lights were turned off, so there was no additional engine load to explain RPM changing.

I've done a lot of searching on Google for what the root cause might be. People have suggested it could be a clogged up IAC valve, but I don't think Toyota Valvematic engines have an IAC valve. It could also be a faulty throttle position sensor, but then I'd expect the problem to occur all the time, not just for a few seconds after a cold start. I removed the air intake and checked the throttle body - it's very clean. I cleaned the MAF sensor as a precaution. Some BMW engines exhibited the same problem (from new) and in that case I gather it was resolved with an ECU software update.

On the occasions when it was really bad, I didn't have my phone ready to capture it on video, but yesterday I recorded two examples with somewhat minor symptoms and have uploaded them to YouTube:

 

[Goran3456]

Check your intake pipes after air filter for cracks, also all vacuum pipes. If there is a crack or a hole, it could cause uneven idle speed. Also it does not hurt to check your spark plugs.

[avensisnz]

2 minutes ago, Goran3456 said:

Check your intake pipes after air filter for cracks, also all vacuum pipes. If there is a crack or a hole, it could cause uneven idle speed. Also it does not hurt to check your spark plugs.

Would a vacuum leak not cause idle speed issues all the time, rather than just for a few seconds after a cold start? Actually, it idles perfectly after a cold start as well. It only does this for a few seconds after you start moving and then depress the clutch and brake to come to a stop, then it idles perfectly until the next cold start.

[avensisnz]

So I unplugged the MAF sensor before starting the car this morning and the idle speed was rock solid - no bouncing up and down. I don't know whether that indicates the MAF sensor is faulty or whether the ECU was simply running in "open loop" mode with the sensor unplugged. A side effect of unplugging the MAF sensor was the instrument cluster lit up like a Christmas tree with five different warning lights! Plus there was an error message that said "Check parking brake system." When I got home tonight I plugged the MAF sensor back in, but that didn't clear the warnings on the dash (even after turning the ignition off). I had to disconnect the Battery to reset everything. I then went through an "idle relearn" procedure I found online, which I'm not actually sure is required on modern Toyotas, but there's no harm in trying. I'll have to wait for the next cold engine start tomorrow morning to see whether it's back to its old tricks or not.

[furtula]

If MAF is offline, then the car goes by default values already programmed in. This in turn uses  a bit more fuel, as the car cant adjust the values on the fly.

 

Try cleaning the MAF with those special spray cleaners. I had similar issue last year, the sensor looked pretty clean, i did spray it good with the cleaner, and i had no issues after plugging it back in. 

Be sure you don't touch the actual sensor wire while working with it.

[avensisnz]

I'd already cleaned the MAF sensor and it didn't help. Do you think the fact it idles perfectly without the MAF sensor plugged in points to a faulty MAF sensor?

After plugging the MAF sensor back in and disconnecting the Battery for a while, the cold idle was back to its old tricks at the next cold start.

To clarify what happens:

1. Start the engine from cold and it idles perfectly
2. Drive off and once the vehicle speed reaches about 15km/h you hear a clunk sound as the ABS performs its self-test
3. Only after that, when you depress the clutch pedal does the idle bounce up and down 3-5 times
4. It continues to idle perfectly after that

It hardly sounds like it's worth worrying about, but it's clearly not normal.

[furtula]

Idling perfectly while cold, and while hot is not the same, as the car is dumping more fuel until it reaches operating temperature.

You don't mention anything about the issue when warm, so i presume it only manifests itself on cold starts.

When you depress the clutch, you apply the load to the engine, turning inside gears + oil in transmission is cold, so, the car tries to adjust to this. If you say that once the MAF was unplugged, and you drove the car, it was all fine, i'd try replacing the sensor.  I don't really know how expensive it is, but you also might consider a 2nd hand one.

[avensisnz]

Depressing the clutch means pushing the clutch pedal down, so the gearbox is disconnected from the engine.

It idles perfectly when both cold and hot, except for the RPM bouncing up and down 3-5 times the first time you come to a stop after a cold start. I also find it interesting that it only does it after the ABS self-check.

MAF sensors are quite expensive.

[avensisnz]

I hate it when people post an issue on a forum like this and then never post an update with the solution, so here I am again!

I decided to take a chance on replacing the MAF sensor, since I found you could order a genuine Denso MAF sensor from rockauto.com for a low price. This is a US website, but Toyotas (like a lot of brands) share a lot of parts across their model ranges. I entered the Toyota part number for the MAF sensor in their search box and it returned the correct part, but with the Denso OEM part number. Anyway, the new MAF sensor made no difference. I assume the problem was masked when unplugging the MAF sensor by the ECU going into some kind of failsafe mode.

The next thing I tried was to remove the throttle body and give it a thorough clean. It wasn't in a bad state, but now it's spotless. I then reconnected the Battery and left the engine running for about 10 minutes with no electrical load to allow the ECU to go through the idle relearn process. The result of this is the cold idle hunting seemed to stop for a few days, but then it gradually returned. Interesting.

At this point I made contact with the selling dealer (I purchased the car from a dealer in another town, about a 90 minute drive away). They authorised me to take the car to my local Toyota dealer for up to one hour of diagnostic time. I left the car with them overnight so they could start it from cold. The service manager called me today to say they think they've identified the fault. They hooked up their diagnostic equipment to the car when they started it and captured the live data. Fortunately they were able to witness the cold idle hunting and the data they captured indicates that at the time of the idle hunting, the Valvematic controller wasn't functioning properly. At this point they called the selling dealer to discuss it further. Unfortunately the selling dealer has declined to replace the Valvematic controller at this stage, because the Toyota dealer can't guarantee this will solve the problem and the cost to replace the part is about NZ$1,800 (900 pounds). I can sympathise with them, because that price is daylight robbery. You could buy an entire second hand engine for that much. I expect I'll be discussing it with them next week, but I'd be quite happy with a second hand Valvematic controller being fitted, if they can find one.

To cap it all off, after I got home from the Toyota dealer today, I noticed both my headlights are damaged. It looks like some kind of glue or solvent came into contact with the headlights and has eaten into the plastic. The left one is particularly bad (photo attached). I just hope they accept liability.

[avensisnz]

I forgot to mention, there's another symptom I experience when the engine is warmed up, which I think also points at the Valvematic controller. If the engine is under load, then I depress the clutch pedal, the engine revs briefly shoot up, then drop way down, then return to the correct idle speed.

[avensisnz]

I did some research on the headlight damage, because the glue/solvent theory didn't make sense. What I suspect may have happened is the mechanic who was working on my car put a protective cover over the front of the car and while the engine was running the automatic headlights switched on. Toyota warns against covering the headlights for more than three minutes, because the head build-up will start melting the lens. The fact that the damaged areas are directly in front of both low beam bulbs aligns with this theory. I've emailed the dealer and expect I'll hear back from them on Monday.

[Dean808]

Did you ever get this issue sorted I am have same problem with my 1.8 petrol t27

[Konrad C]

On 8/14/2021 at 12:04 AM, avensisnz said:

I did some research on the headlight damage, because the glue/solvent theory didn't make sense. What I suspect may have happened is the mechanic who was working on my car put a protective cover over the front of the car and while the engine was running the automatic headlights switched on. Toyota warns against covering the headlights for more than three minutes, because the head build-up will start melting the lens. The fact that the damaged areas are directly in front of both low beam bulbs aligns with this theory. I've emailed the dealer and expect I'll hear back from them on Monday.

Learned something new. If this can happen, I would make a note to turn off the auto lights and auto wipers to reduce the risk of this happening. Even though this happened in New Zealand, I am sure UK dealers may be aware! 

I have never had the idle fluctuating during warm up, only the momentary high idle when coming to a stop with a warm engine, once in a while.

[avensisnz]

2 minutes ago, Konrad C said:

Learned something new. If this can happen, I would make a note to turn off the auto lights and auto wipers to reduce the risk of this happening. Even though this happened in New Zealand, I am sure UK dealers may be aware! 

With lots of cars having automatic headlights these days, it's something you'd expect a franchise dealer to always check.

I was pleasantly surprised to receive a phone call from the workshop foreman to say he agrees with my theory of what happened and has two brand new headlights on order. Part of me was expecting a legal battle on my hands.

[avensisnz]

7 hours ago, Dean808 said:

Did you ever get this issue sorted I am have same problem with my 1.8 petrol t27

As I said in a previous post, the Toyota dealer diagnosed a faulty Valvematic controller. It's a ridiculously expensive part and because they can't 100% guarantee that's what's causing the idle issue, the dealer I purchased the car from isn't prepared to authorise the repair unless the problem gets worse.

I had wondered if it might be a fault with the electronic throttle body. Someone posted about the exact same issue on an Audi forum and how they fixed it:

https://www.audiforums.com/forum/audi-a8-10/cold-start-idle-bounce-2-4-times-141756/

Basically, they removed the cover from the throttle body and cleaned the electrical contacts. As simple as that. The only problem for us is the cover on the Toyota throttle body is secured by rivets, so you can't remove it.

If you want to take a chance on it, you can order a new throttle body from RockAuto in the USA for a really low price (their international shipping is quite cheap and really fast). The part is common with many Toyotas. Here's a link:

https://www.rockauto.com/en/partsearch/?partnum=2203037050

It's super-easy to unbolt the throttle body and install a new one, except for the fact you have to drain the coolant, as there's a coolant line going through the throttle body.

 

[Cyker]

13 hours ago, avensisnz said:

With lots of cars having automatic headlights these days, it's something you'd expect a franchise dealer to always check.

I was pleasantly surprised to receive a phone call from the workshop foreman to say he agrees with my theory of what happened and has two brand new headlights on order. Part of me was expecting a legal battle on my hands.

Wow that's incredible! Major props to them for taking responsibility! I wish more dealers were like this!

[avensisnz]

Hey guys, I've come back to report the "cold idle bounce" issue has been resolved! After reading about an Audi owner with exactly the same problem ( https://www.audiforums.com/forum/audi-a8-10/cold-start-idle-bounce-2-4-times-141756/ ) I took a punt and ordered a new throttle body assembly for my Avensis. Not a genuine Toyota part, mind you, as the price was ridiculous, but a new after market part from rockauto.com.

Unlike the Audi throttle body shown in the link above, the plastic cover on the Toyota throttle body is secured by rivets, so I couldn't simply unclip the cover and clean the electrical contacts inside.

Installation was super-easy, as per this video:

 

[avensisnz]

I don't believe this. 11 days after installing the new throttle body, the original problem has returned!

The Toyota dealer suspected an issue with the Valvematic controller, but I don't believe this is the case. A fault with the Valvematic controller should result in a fault code and check engine light, which I don't have. In addition, you'd expect drivability issues, e.g. a lack of power. My engine performs perfectly at all engine speeds.

What I do know is if you unplug the MAF sensor, the problem goes away. With the MAF sensor unplugged, the ECU will run in "open loop mode," meaning it ignores all sensor readings and uses fixed settings for things like ignition timing and air/fuel ratio. I've already replaced the MAF sensor, by the way.

I had found this other thread discussing the same issue affecting other *brand new* Toyotas with a 1.8 litre petrol engine and manual gearbox, but apparently only in sub zero temperatures. I wonder if it isn't an ECU programming issue, where certain sensor inputs result in it having trouble setting the correct idle speed?

https://www.toyotanation.com/threads/idle-hunting-when-cold.120207/

I'm loathe to spend any more money randomly swapping parts, but wonder if it might be the coolant temperature sensor?