Weird cold start issue

[LS1VT]

Lately my vyss has issues on initial cold start up. It will start straight away, idle normal for a 20 seconds, then spike for a second or two, then back to normal. Once I put in drive, it will surge & stumble for a few seconds then get a check engine light with fans on. Ten seconds later, light & fans switch off & all good. No problems after that & drives normal but will do it again the next cold start. It has new spark plug leads & wires. I used a scanner to check for codes but showed nothing. I can't see or hear any any vacum leaks.I don't drive the car much as I only use on some weekends. The mods are cam & heads, full exhaust & otr. Has anyone had a similar problem? Any ideas?

[whitels1ss]

Very unusual, with the fans coming on & engine light coming on

I may well be way off track here but
I would be checking the coolant temperature sensor, perhaps it is faulty and spiking,
showing extra overheat hot at a point in the warming up of the engine and then reading correct to get back to normal afterwards?

I would connect my scanner and watch the coolant temperature reading to see if it shows something unusual as the engine warms up.

Sorry, I could be way off but I think it is somewhere to look.

Best of luck!

[Peter B - CV8]

Very unusual, with the fans coming on & engine light coming on

I may well be way off track here but
I would be checking the coolant temperature sensor, perhaps it is faulty and spiking,
showing extra overheat hot at a point in the warming up of the engine and then reading correct to get back to normal afterwards?

I would connect my scanner and watch the coolant temperature reading to see if it shows something unusual as the engine warms up.

Sorry, I could be way off but I think it is somewhere to look.

Best of luck!

I agree with your suggestion re the coolant temp sensor (because of the fans coming on). If it was just an idle issue I'd suggest removing & cleaning the throttle body - including removing the Idle Control Valve + also checking for any split /perished emissions intake hoses.

[LS1VT]

I was thinking the same thing about the coolant temp sensor. I might replace it & see if it helps.
Another question, if a check engine light comes on for whatever reason, do fans usually turn on automatically?

[Peter B - CV8]

No, it's not an automatic feature

[whitels1ss]

I was thinking the same thing about the coolant temp sensor. I might replace it & see if it helps.



Another question, if a check engine light comes on for whatever reason, do fans usually turn on automatically?

Hey, as I said I may be way off with that idea but at least it's something as a starting point.

No, as far as the fans go, as Peter B said, fans do not come on automatically with engine light.

[VXSS346]

Are you sure a code wasn't logged? It really should log a code whenever the engine light comes on.
Might be worth plugging it in again and double checking? Otherwise plug it in and just clear any codes (whether they exist or not) and next time you start it and it does it, check the fault codes again.

Not suggesting its necessarily an ECU fault, but if its not logging a code after an engine light, that's not good.

Other than that, I'm guessing any genuine code that would also turn on the fans would be related to either the Coolant temp sensor circuit or maybe something to do with the A/C.

Keep us posted. Good luck.

[whitels1ss]

Does the temp gauge on the instrument cluster do anything strange when it plays up?

[LS1VT]

I haven't noticed anything wierd with the temp gauge.

[LS1VT]

Hey, as I said I may be way off with that idea but at least it's something as a starting point.

No, as far as the fans go, as Peter B said, fans do not come on automatically with engine light.

It's all good, I was thinking the same thing. I do appreciate the help.

[LS1VT]

Are you sure a code wasn't logged? It really should log a code whenever the engine light comes on.
Might be worth plugging it in again and double checking? Otherwise plug it in and just clear any codes (whether they exist or not) and next time you start it and it does it, check the fault codes again.

Not suggesting its necessarily an ECU fault, but if its not logging a code after an engine light, that's not good.

Other than that, I'm guessing any genuine code that would also turn on the fans would be related to either the Coolant temp sensor circuit or maybe something to do with the A/C.

Keep us posted. Good luck.

Yeah I tried a couple of times but showed nothing. Maybe it clears itself when light goes out? Or maybe my ob2 scanner isn't compatible?
In the next few days I'll change the temp sensor & I'll let you know if it works or not.

[LS1VT]

I agree with your suggestion re the coolant temp sensor (because of the fans coming on). If it was just an idle issue I'd suggest removing & cleaning the throttle body - including removing the Idle Control Valve + also checking for any split /perished emissions intake hoses.

It's just weird that after about a minute or 2 it's all fine

[Toddler78]

When you start the car start it in diagnostic mode and set the display to show the digital temp then you can watch in real time what the temp is displaying.

By guess is a buggered o2 sensor forcing the the engine to maybe run lean then rich as it try’s to adjust fuel trims.

[Peter B - CV8]

When you start the car start it in diagnostic mode and set the display to show the digital temp then you can watch in real time what the temp is displaying.

By guess is a buggered o2 sensor forcing the the engine to maybe run lean then rich as it try’s to adjust fuel trims.

Maybe, but I don't think that would trigger the cooling fans to come on ??

[Toddler78]

Maybe, but I don't think that would trigger the cooling fans to come on ??

Maybe not but we’re all assuming the one issue is causing both symptoms.

Just a thought, never owning an auto he said it plays up wheen put on drive. Could it be a trans converter on its way out or not pumping fluid or even fluid low, that might explain the surging and could explain the thermos turning on as the fluid runs through the radiator?