Hi

Im a little baffled, since I have owned the car 33,000 miles ago now 119,000 miles the revs would often go up a little on tick over, this has progressively got worse recently so after a good carb cleaner through the system, oil to throttle cable I changed the petrol cap to a new genuine one, this has increased the problem a little more so I removed the Idle control valve and cleaned, this made it even worse so purchased a new one and now fitted, I now have the following issue.

It starts great and ticks over at around 1200 till warm then drops to 850 ish.

The problem then starts with a tick over of nearly 2000 but doesn't fluctuate.

If I turn the engine off for a while and restart I then have it running at 850 ish.

Im thinking coolant temperature sensor ??

anyone else had this problem please.

Thank you

Michael

it could be the idle control valve. Thoroughly cleaning the throttle body may help.

Also check the MAF sensor. A quick forum search will give a "how to" for that.

I would change the coolant sensor, they are reasonably cheap after all.
a tip to prevent coolant loss when changing it, remove the header tank cap and put some cling film or thin plastic over the opening replace the cap, this will form a seal and help prevent coolant from running out of the sensor port...still be ready with a collector just in case though!

not quite sure in the thinking behind the coolant sensor

First off there's only ones for the ECU and gauge. Wouldn't you see the gauge misbehaving

the car starts and warms up correctly

"It starts great and ticks over at around 1200 till warm then drops to 850 ish."


I don't know what the fault is. I would start by looking at the actual and expected revs on a scanner


I would also look at the throttle position while at 850 rpm and 200 rpm

cable operated on a 1.2 07 ?

"I changed the petrol cap to a new genuine one, this has increased the problem a little more"

Are you sure.

what happens if you put the old one back

the only thing connected to the the cap is the evap system

this is easy to temp disable and plug just for testing. The solenoid does fail if overfilled

things like the ICV can be tested via software

before playing parts darts.

The revs sit higher when the engine is cold. Yours drop as it warms up so the temperature sensor is probably ok.

Fuel is injected -
(1) When the driver asks for power. When the driver takes their foot off the pedal no fuel is delivered.
(2) Below about 1500 revs when the idle control valve takes over.

Normal operation - Engine spinning, remove your foot, the revs drop quickly to about 1500, there is a note change as the ICV kicks in and the revs drop gently to tickover.

If the ICV is not behaving, the revs will drop a lot lower and there wont be that change in note at around 1500 revs.

koalar said:

not quite sure in the thinking behind the coolant sensor
First off there's only ones for the ECU and gauge. Wouldn't you see the gauge misbehaving

Click to expand...

The gauge is not accurate and is damped against fluctuations, the ECU is reading the returned voltage from the sender, a high (or low depending on the sensor configuration) resistance will cause the voltage to change from what the ECU expects to see so it increases the fueling to compensate. It is a well known fault on many other makes of vehicle.

09 johno said:

The gauge is not accurate and is damped against fluctuations, the ECU is reading the returned voltage from the sender, a high (or low depending on the sensor configuration) resistance will cause the voltage to change from what the ECU expects to see so it increases the fueling to compensate. It is a well known fault on many other makes of vehicle.

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the original poster states the car start and idles fine at 1.2K which is correct

then as it warms up drops to 850 which is correct

then start to idle at 2K which isnt correct

for a coolant sensor I would expect
over or under fuelling, White or black smoke
poor economy or over heating
rough running
mismatch from the ambient sensor throwing a engine light

even then I would be dubious as most of the fuelling is controlled by the ambient temperature sensor

plus the temperature gauge is reading high enough for the fuelling to be controlled from the O2 sensor


with the evidence we are given its point me in a different direction but I might be wrong


should be fairly simple if you read the live data. Coolant, expected revs, actual revs, throttle position, O2 sensors, throttle pedal position sensor if it has one.


might just need a relearn as the throttle body been apart or throttle position sensor


without some feed back we are pissing in the wind If I suspected the coolant sensor its would be easy enough to test with a fridge, boiling water and a multi meter before playing parts darts game.

I suggested the idle control valve because it sits open when when cold, only moving accurately when the revs drop to normal tickover. Also check the O2 sensors as they are switched out of circuit when cold. Air leaks in inlet manifold (and sometimes exhaust pipe after sensor) can cause tickover issues.

Michaegreenslade said:

Hi

I removed the Idle control valve and cleaned, this made it even worse so purchased a new one and now fitted, I now have the following issue.

It starts great and ticks over at around 1200 till warm then drops to 850 ish.

Thank you

Michael

Click to expand...

DaveMcT said:

it could be the idle control valve. Thoroughly cleaning

Click to expand...

DaveMcT said:

I suggested the idle control valve because it sits open when when cold, only moving accurately when the revs drop to normal tickover.

Click to expand...

but its been cleaned

and been changed

although its not normal first move as its not a bolt on part ????

The ICV is part of the throttle body so should get cleaned when the TB job is done. Also look for air leaks on the engine side of the thottle. Tramp air causes the engine to rev because fuel is injected according air going through the engine.

I had this exact problem on the wife's Dynamic so not sure if it will be the same on yours but I'll explain anyways

I changed quite a few sensors to try to fix this issue. Brand new (or so I was led to believe, more on this in a mo) throttle body with all associated sensors, MAP sensor, lambda sensor; none of which cured it.


Eventually I took even more of a shot in the dark and replaced the "new" throttle body with a guaranteed working one from a breaker.

It now ticks over and runs beautifully

Wazzzer said:

I had this exact problem on the wife's Dynamic so not sure if it will be the same on yours but I'll explain anyways

I changed quite a few sensors to try to fix this issue. Brand new (or so I was led to believe, more on this in a mo) throttle body with all associated sensors, MAP sensor, lambda sensor; none of which cured it.


Eventually I took even more of a shot in the dark and replaced the "new" throttle body with a guaranteed working one from a breaker.

It now ticks over and runs beautifully

Click to expand...

cable operated or fly by wire throttle body ???

Cable

The restarting hot and running normal could be the key.

I had a 57 plate 1.1 active a few years ago and it did something similar.
It cold started ok, then as it warmed up it ran rich and idled fast until I restarted it hot, then it ran ok.

I logged the fueling status from cold start and noticed as it warmed up it wouldn't trip into Closed Loop. It went from Open Loop to Open Loop - system fault (a fail system mode).
When restarting hot it went striaght to Closed Loop and ran ok, until the next cold start.

Turned out the heater element of the upstream O2 was faulty, I just swapped it with the downstream sensor (same part) and it was back to normal.

The whole thing had me scratching my head as I never had any EML's, codes or pending codes, but the only thing I could pinpoint that affected the fueling so soon in the cycle was the O2, just at the point it should have switched over to Closed Loop it failed to kick in.

any update ?

koalar said:

any update ?

Click to expand...

From who..?

original poster

several suggestions give


but no feed back as to whether the problem still persists