Rough Idle - tried many things.

[Kind Panda]

I've got a 2004 Avensis 1.8 VVTi petrol that I purchased last month. It's currently got 66000 miles on the clock and apart from this idle issue I'm generally happy with the vehicle. 

The symptoms the car exhibits once warm is an idle that drops to 600 RPM which makes the car vibrate, there may also be a separate or interlinked issue involving the main cooling fan operating periodically and quite frequently, more so than any other car I've owned or driven. 

So far I've changed the fuel to premium Shell 'V-Power', I've changed the spark plugs, I've cleaned the MAF sensor and the throttle body - all have made no difference. I purchased an OBD II port reader to ascertain if there were any fault codes associated, but this was negative. Really scratching my head at this point! I feel the only thing left is to run the car until it throws a fault code, or to adjust the throttle cable - which I feel is not appropriate as it's not likely the root of the problem. 

..or I could formally reject the car under the sales of goods act - the dealer has already told me to Foxtrott Oscar when I took it back under 'warranty' so it'd be a load of hassle in the small claims court no doubt. 

Grateful for any advice.

[FROSTYBALLS]

Welcome to Toyota Owners Club.

As you bought the car last month, the Consumer Rights Act 2015 applies rather than the Sale of Goods Act - 

 

[fastbob72]

What's the idle and full throttle percentages when you have the OBD2 reader plugged in, assuming it can display live data. At idle the throttle % should be 11.8%,full throttle @ 78% if your throttle position sensor is working properly.

 

Also have you tried checking all your vacuum lines,PCV valve and associated hoses??

 

BTW, the 1.8 vvti Avensis do idle around 650rpm normally anyway and you may or may not have noticed they have an alarming (initially until you get used to it) habit of the revs dropping very low when you fully engage the clutch pulling away in 1st. You let up the clutch expecting to pull away from a junction or roundabout and the revs drop away necessitating the application of more revs before stalling or at least a display of an embarrassing bout of kangaroo petrol like when you very first drove a car.

 

Also, it is interesting come to think of it that you mention the cooling fans come on, this shouldn't happen till around 96 degrees coolant temp or above and in my experience the vvt-i's normal operating temp is around 86°. Mine needs to sit in stop start traffic for a little while before it reaches the kind of temp needing to operate the cooling fans, even just sitting idling this takes some time.

Now, when the cooling fans kick in or the A/C, heater, lights, wiper combo etc the idle speed should automatically increase slightly to compensate for the sudden draw on the alternator.Could there be a link between the fans coming on, maybe the ECU isn't increasing idle speed to compensate??

Also, the coolant fans themselves. Are they coming on too early or is the engine running hotter than the average vvt-i's motor. OK, not every engine especially when their 12 years old or more despite being the same kind will operate identically but it shouldn't be running at coolant fan temp generally so that would suggest problems with the engine itself.

Again assuming your OBD2 fault code reader can display live data it'd be worth letting it idle, heat up and get a feel for the engine general operating temp and at what temp the fans kick in.

Edited November 2, 2016 by fastbob72
to add a couple of more points

[Kind Panda]

50 minutes ago, fastbob72 said:

What's the idle and full throttle percentages when you have the OBD2 reader plugged in, assuming it can display live data. At idle the throttle % should be 11.8%,full throttle @ 78% if your throttle position sensor is working properly.

Unfortunately my reader is the most basic - it reads codes, clears them and clears dash lights. 

Also have you tried checking all your vacuum lines,PCV valve and associated hoses?

I ruled out vacuum leaks as the idle was not increasing nor the engine stalling. 

BTW, the 1.8 vvti Avensis do idle around 650rpm normally anyway and you may or may not have noticed they have an alarming (initially until you get used to it) habit of the revs dropping very low when you fully engage the clutch pulling away in 1st. You let up the clutch expecting to pull away from a junction or roundabout and the revs drop away necessitating the application of more revs before stalling or at least a display of an embarrassing bout of kangaroo petrol like when you very first drove a car.

 

Also, it is interesting come to think of it that you mention the cooling fans come on, this shouldn't happen till around 96 degrees coolant temp or above and in my experience the vvt-i's normal operating temp is around 86°. Mine needs to sit in stop start traffic for a little while before it reaches the kind of temp needing to operate the cooling fans, even just sitting idling this takes some time.

Now, when the cooling fans kick in or the A/C, heater, lights, wiper combo etc the idle speed should automatically increase slightly to compensate for the sudden draw on the alternator.Could there be a link between the fans coming on, maybe the ECU isn't increasing idle speed to compensate??

Idle rises to about 900 RPM when the main beam lights are operating. 

Also, the coolant fans themselves. Are they coming on too early or is the engine running hotter than the average vvt-i's motor. OK, not every engine especially when their 12 years old or more despite being the same kind will operate identically but it shouldn't be running at coolant fan temp generally so that would suggest problems with the engine itself.

The fan is operating way too early in my opinion and multiple times per journey, even on a short journey (10 miles? from cold) and relatively cool days. Having never owned an Avensis before I wasn't sure if this was a normal. I agree the fans shouldn't be cooling the rad in this case but no idea where to go from here. 

Again assuming your OBD2 fault code reader can display live data it'd be worth letting it idle, heat up and get a feel for the engine general operating temp and at what temp the fans kick in.

 

[frankie406]

Take out pcv from engine to throttle body clean the pcv with brake cleaner/throttle body cleaner and shake it you should hear the rattle of a ball inside if it doesn't work you need a new pcv.take out the throttle body clean both side's and the idle control(throttle body cleaner).do all hoses from air filter right through to the engine. Check for cracks or splits. Chuck in some miller's eco max cleaner into the tank.

[WALLOP]

 

My 2007 1.8vvti estate used to fluctuate between 600 and 800 rpm when idling and would give the same shudder when too low before self correcting and then going through the whole sequence again.

I thoroughly cleaned the mass airflow sensor with no benefit but once replaced with a new O.E unit the problem was solved. The original one looked perfectly clean with no obvious deposits but they can obviously develop faults over time. Mine had done 63000 miles when the fault developed.