Yaris hesitation when cold

#1

2002 Toyota Yaris 1.5 T-Sport
Engine code 1NZ-FE

The car suffers from a hesitation when first pulling away after a cold
start, and occasionaly when changing up a gear. It misfires and feels like
it will stall, but never does. Once the engine has a slight warmth, the
problem disappears and the car runs perfectly. This takes about a mile,
perhaps less, and it revs freely right from the word go, the problem is
only apparent as one transfers load to the engine. The symptom is very much
like the way a cold carb fed engine would perform with insufficient choke.

This problem first started when I replaced the OEM Denso plugs with NGKs:

Denso chart recommendation: K16R-U gapped at 0.8mm (that is straight from
their website. Autodata contradicts this and says to use K16R-U11 with
1.1mm gap. The car was fitted with K16R-U when I acquired it.)

NGK recommendation: BKR5EY-11 gapped at 1.1mm

So, since they appeared to cause the prob, I removed the NGKs and got a new
set of Densos, gapped them at 0.8mm, fitted them and the problem
disappeared. For about 2k miles. Now, it has returned, yet the plugs are
still like brand new and the gaps are still correct. Deposits are the
normal light grey, with no fouling or evidence of poor combustion.

Could it be that the plugs are a red herring and the car has some other
problem? Checks I have done so far are:

- Checked for intake air leaks using soapy water. Found none.
- Measured coil resistances, all four are between 21 and 23K
- Checked readout from CTS via OBD scan. Reads normally, i.e. around
ambient temp when cold, rising to 80-90deg warmed up.
- Checked intake air temp readout as above. Reads ambient temp with a cold
engine.
- Checked for any stored DTCs. None present.
- Measured TPS voltage: 0.54V closed, rising to 3.87V at WOT. No dead
spots.

Any other ideas, please? It's a very small issue but doesn't seem right for
an EFi car.

#2

On Fri, 06 Nov 2009 16:29:10 -0000, Stu <nospam (AT) thanks (DOT) com> wrote:

Quote:

2002 Toyota Yaris 1.5 T-Sport
Engine code 1NZ-FE

The car suffers from a hesitation when first pulling away after a cold
start, and occasionaly when changing up a gear. It misfires and feels
like
it will stall, but never does. Once the engine has a slight warmth, the
problem disappears and the car runs perfectly. This takes about a mile,
perhaps less, and it revs freely right from the word go, the problem is
only apparent as one transfers load to the engine. The symptom is very
much
like the way a cold carb fed engine would perform with insufficient
choke.

This problem first started when I replaced the OEM Denso plugs with NGKs:

Denso chart recommendation: K16R-U gapped at 0.8mm (that is straight from
their website. Autodata contradicts this and says to use K16R-U11 with
1.1mm gap. The car was fitted with K16R-U when I acquired it.)

NGK recommendation: BKR5EY-11 gapped at 1.1mm

So, since they appeared to cause the prob, I removed the NGKs and got a
new
set of Densos, gapped them at 0.8mm, fitted them and the problem
disappeared. For about 2k miles. Now, it has returned, yet the plugs are
still like brand new and the gaps are still correct. Deposits are the
normal light grey, with no fouling or evidence of poor combustion.

Could it be that the plugs are a red herring and the car has some other
problem? Checks I have done so far are:

- Checked for intake air leaks using soapy water. Found none.
- Measured coil resistances, all four are between 21 and 23K
- Checked readout from CTS via OBD scan. Reads normally, i.e. around
ambient temp when cold, rising to 80-90deg warmed up.
- Checked intake air temp readout as above. Reads ambient temp with a
cold
engine.
- Checked for any stored DTCs. None present.
- Measured TPS voltage: 0.54V closed, rising to 3.87V at WOT. No dead
spots.

Any other ideas, please? It's a very small issue but doesn't seem right
for
an EFi car.

Plug leads?

#3

On Fri, 06 Nov 2009 16:29:10 -0000, Stu <nospam (AT) thanks (DOT) com> wrote:

Quote:

2002 Toyota Yaris 1.5 T-Sport
Engine code 1NZ-FE

The car suffers from a hesitation when first pulling away after a cold
start, and occasionaly when changing up a gear. It misfires and feels
like
it will stall, but never does. Once the engine has a slight warmth, the
problem disappears and the car runs perfectly. This takes about a mile,
perhaps less, and it revs freely right from the word go, the problem is
only apparent as one transfers load to the engine. The symptom is very
much
like the way a cold carb fed engine would perform with insufficient
choke.

This problem first started when I replaced the OEM Denso plugs with NGKs:

Denso chart recommendation: K16R-U gapped at 0.8mm (that is straight from
their website. Autodata contradicts this and says to use K16R-U11 with
1.1mm gap. The car was fitted with K16R-U when I acquired it.)

NGK recommendation: BKR5EY-11 gapped at 1.1mm

So, since they appeared to cause the prob, I removed the NGKs and got a
new
set of Densos, gapped them at 0.8mm, fitted them and the problem
disappeared. For about 2k miles. Now, it has returned, yet the plugs are
still like brand new and the gaps are still correct. Deposits are the
normal light grey, with no fouling or evidence of poor combustion.

Could it be that the plugs are a red herring and the car has some other
problem? Checks I have done so far are:

- Checked for intake air leaks using soapy water. Found none.
- Measured coil resistances, all four are between 21 and 23K
- Checked readout from CTS via OBD scan. Reads normally, i.e. around
ambient temp when cold, rising to 80-90deg warmed up.
- Checked intake air temp readout as above. Reads ambient temp with a
cold
engine.
- Checked for any stored DTCs. None present.
- Measured TPS voltage: 0.54V closed, rising to 3.87V at WOT. No dead
spots.

Any other ideas, please? It's a very small issue but doesn't seem right
for
an EFi car.

Or more relevantly, try looking under the hood in the dark & seeif you can
see any tracking from the coils

#4

Stu wrote:

Quote:

2002 Toyota Yaris 1.5 T-Sport
Engine code 1NZ-FE

The car suffers from a hesitation when first pulling away after a cold
start, and occasionaly when changing up a gear. It misfires and feels
like it will stall, but never does. Once the engine has a slight
warmth, the problem disappears and the car runs perfectly. This takes
about a mile, perhaps less, and it revs freely right from the word
go, the problem is only apparent as one transfers load to the engine.
The symptom is very much like the way a cold carb fed engine would
perform with insufficient choke.

This problem first started when I replaced the OEM Denso plugs with
NGKs:

Denso chart recommendation: K16R-U gapped at 0.8mm (that is straight
from their website. Autodata contradicts this and says to use
K16R-U11 with
1.1mm gap. The car was fitted with K16R-U when I acquired it.)

NGK recommendation: BKR5EY-11 gapped at 1.1mm

So, since they appeared to cause the prob, I removed the NGKs and got
a new set of Densos, gapped them at 0.8mm, fitted them and the problem
disappeared. For about 2k miles. Now, it has returned, yet the plugs
are still like brand new and the gaps are still correct. Deposits are
the normal light grey, with no fouling or evidence of poor combustion.

Could it be that the plugs are a red herring and the car has some
other problem? Checks I have done so far are:

- Checked for intake air leaks using soapy water. Found none.
- Measured coil resistances, all four are between 21 and 23K
- Checked readout from CTS via OBD scan. Reads normally, i.e. around
ambient temp when cold, rising to 80-90deg warmed up.
- Checked intake air temp readout as above. Reads ambient temp with a
cold engine.
- Checked for any stored DTCs. None present.
- Measured TPS voltage: 0.54V closed, rising to 3.87V at WOT. No dead
spots.

Any other ideas, please? It's a very small issue but doesn't seem
right for an EFi car.

you cannot check for inlet leaks with soapy water, the leak will be sucking,
not blowing, check for inlet leaks using a flammable liquid or gas, carb.
cleaner is convenient with the engine running, any leaks that you spray over
will cause a speed variation.

running the larger gap may have caused a tracking issue, which may have
damaged one or more coils.

#5

Quote:

The car suffers from a hesitation when first pulling away after a cold
start, and occasionaly when changing up a gear. It misfires and feels
like it will stall, but never does.
Plug leads?

I finally got around to replacing my plug leads last week, after
putting up with my ageing Hyundai Accent doing exactly the same thing
for a few months.

Changing the leads appears to have sorted it :-)

#6

Colin Wilson wrote:

Quote:

The car suffers from a hesitation when first pulling away after a
cold start, and occasionaly when changing up a gear. It misfires
and feels like it will stall, but never does.
Plug leads?

I finally got around to replacing my plug leads last week, after
putting up with my ageing Hyundai Accent doing exactly the same thing
for a few months.

Changing the leads appears to have sorted it :-)

I have an idea that the Yaris does not have any plug leads, but ICBW

#7

On Fri, 06 Nov 2009 23:22:32 -0000, Mrcheerful <nbkm57 (AT) hotmail (DOT) co.uk>
wrote:

Quote:

Colin Wilson wrote:
The car suffers from a hesitation when first pulling away after a
cold start, and occasionaly when changing up a gear. It misfires
and feels like it will stall, but never does.
Plug leads?

I finally got around to replacing my plug leads last week, after
putting up with my ageing Hyundai Accent doing exactly the same thing
for a few months.

Changing the leads appears to have sorted it :-)

I have an idea that the Yaris does not have any plug leads, but ICBW

I think it's coil on plug, but they track as well.

--
Duncan Wood

#8

"Mrcheerful" <nbkm57 (AT) hotmail (DOT) co.uk> wrote in
news:AsYIm.2302$Ym4.75 (AT) text (DOT) news.virginmedia.com:

Quote:

you cannot check for inlet leaks with soapy water, the leak will be
sucking, not blowing, check for inlet leaks using a flammable liquid
or gas, carb. cleaner is convenient with the engine running, any leaks
that you spray over will cause a speed variation.

running the larger gap may have caused a tracking issue, which may
have damaged one or more coils.

Thanks for your replies. The ignition is indeed coil-in-cap. I'll start it

under cover of darkness in a couple of days (working nights right now)and
look for any evidence of tracking. At the same time, I'll also check again
for air leaks with whatever flammable spray I can lay my hands on. ;-)

#9

Stu <nospam (AT) thanks (DOT) com> wrote in
news:0vednX1xHqnkhWjXnZ2dnUVZ7qadnZ2d (AT) brightview (DOT) co.uk:

Update

Checked under the bonnet in darkness and nothing is glowing. Done another
check for leaks with a flammable spray and nothing happened. The only idea
I have left is to disable the fuel pump and try the coils on a spare plug,
looking for a weak spark. Any other theories?

#10

Stu wrote:

Quote:

Stu <nospam (AT) thanks (DOT) com> wrote in
news:0vednX1xHqnkhWjXnZ2dnUVZ7qadnZ2d (AT) brightview (DOT) co.uk:

Update

Checked under the bonnet in darkness and nothing is glowing. Done
another check for leaks with a flammable spray and nothing happened.
The only idea I have left is to disable the fuel pump and try the
coils on a spare plug, looking for a weak spark. Any other theories?

it is extremely difficult to see a tracking spark on 'coil on plug'
vehicles, and in any case if the misfire only occurs when the engine is
loaded (ie not when ticking over then there will be nothing to see in any
case.)

I would try a scrupulous clean of each coil pack and spray it well with
wd40, clean the outsides of the plugs well too, and then try it, if there is
an improvement then you are on the right track (no pun intended) the other
problem is that the coil may be tracking internally like mondeo ones do and
then the only way is to substitute with a known good pack.

there is also the possibility that the fault lies somewhere else completely,
such as a tdc sensor.