4age 20 valve flat spot/stumble

[timbuchanan]

I have recently bought a BZ Touring with 97kms on the clock and have noticed that on cold mornings especially, there seems to be a flat spot between 2200rpm and 3000rpm.

With constant light throttle I can feel a slight loss of power. On Light throttle up to 2000rpm and then half throttle (or full throttle) from then on produces a loss of power which then comes fine again by 3000rpm.

The last owner had been running 98, and I accidentally put in one tank of 95, so this might be playing up with the ECU, but I will be running 98 from now on.

The 100km service is now due so I have been getting quotes from local mechanics for the cambelt/waterpump/cam seals/ oil and fuel filter/gear box and engine oil.

I will also ask for the spark plugs to be replaced.

Reading other posts it seems that it could be a sensor of some sort? Is there any reason it would occur at the same rev range?

Once the car has warmed up it is usually fine, but does still do it. Its not a bit loss of power, my fiancé would probably not even notice it, but I just want to have it all going well.

Look forward to your helpful advice

[BigDon]

I would say knock and/or 02 sensor on the way out. I suggest you check the fault codes.

Do a quick search on here for the instructions as there are plenty of threads dealings with these types of issues.

I would change 02 first as they seem to go more commonly than the knock sensors.

I replaced knock and 02 in my last bzg Levin which had similar problems.

Probably time for a new air filter at your 100km service as well plus you might as well do the other belts while they are there. (I'd grab a washable K&N drop in repalcement filter for the factory airbox)

There is a good guy on the boards here (Mark) who can get you cheap genuine toyota parts email him at parts@manawatu.toyota.co.nz

[timbuchanan]

Thanks for that Bigdon

I have asked for prices from Marks for the knock and o2 sensor so as long as they are not too much they will be replaced soon

Hopefully this will sort out the problem!

[Boost_4_Life]

my old blacktop had a terrible stumble between 2000 - 3000 when it was cold. It would only do it once, then it was away and never happened again. I think from what ive seen that particular prob can be common. altho yours must be different if its doing it warm..

[BZR4AGE]

I've solved my problem too replacing the O2 and Knock sensor. I am sure that will solve your problem too

[Subway]

I have this problem as well as I posted in another thread, which o2 sensor did you guys replace yours with? and where did you source them?

[Bling]

Mine does the same thing if the engine is really cold. Never when its a warm day etc, only on the really cold days. Even then not every time so I just ignore it. If you push through the revs to say 4k it comes right I find. Sounds similar to your problem, but I'm not saying its the same thing.

[Boost_4_Life]

Mine does the same thing if the engine is really cold. Never when its a warm day etc, only on the really cold days. Even then not every time so I just ignore it. If you push through the revs to say 4k it comes right I find. Sounds similar to your problem, but I'm not saying its the same thing.

thats exactly what mine was like. it never bothered me much so i didnt do anything about it. i thought i read on here it was a common fault with no exact answer as to the cause... who knows...

[thegreatestben]

Mine hesistates on light/medium throttle from time to time and giving it full throttle seems to get it to come right. Tis real weird and annoying but I've decided it could be a number of small expensive problems and I've just learnt to adapt my driving style to suit

[BigDon]

I replaed mine with OEM Toyota (both knock and 02), sourced through our friendly cheap part man at the time Mr Revhead.

[Crampy]

I believe Matt Dunn can source cheaper replacement O2 sensors.

[timbuchanan]

I went for a big drive last night and after it had been driven hard for 10mins the problem went away.

When I had said it was doing it while warm, this was that the engine had got up to the normal temperature, but maybe not hot enough to fix the small blip.

Mark quoted me $250 for the o2 sensor and $235 for the knock sensor (hope your ok me quoting these here- for future forum searches) and at that price I am happy to live with the problem until it gets worse

Will there be any damage caused by not replacing these?

[neo]

Mines done that since it come into the country 7 years ago. It spent a week at the auto sparky and they checked the O2 and said it was fine..

Maybe its just the knock sensor?

Its just a winter thing Ive learnt to put up with lol

[timbuchanan]

Thanks Neo

Now that i know its a common occurrence with 20 valve engines then I will just accept it as a querk. It will be worse since im in 'sunny' Dunedin