Poor cold running throttle response til warm

[Chim_Pete]

Hey all,

Done a search but could find any similar probs to this...

In ambient temperatures below ~10degC my chim starts fine but isn't very happy until after about 4-5mins of stationary warm up time. When you gently touch the throttle the revs die instead of rising, but if you poke the throttle you can blip the revs and then hold it at a fast idle. Then after about 3-5mins (depending on how cold it is) something must change, i.e. a sensor value or valve or something because then it responds normally. If it is left idleing you can hear a subtle change in the engine noise when this happens - I haven't put my finger on how to describe this yet...

Also if you stall it during this warm-up time, it won't want to restart for at least 5mins (I don't know if this is related or not).

I have been told once that "they do that sir", but something can't be right in my opinion.

Any tips on things to check/try gratefully recieved.

Cheers,

Pete.
1995 Chim 400

[MADMAX2]

Chim_Pete said:

Also if you stall it during this warm-up time, it won't want to restart for at least 5mins (I don't know if this is related or not).1995 Chim 400

Might be worth fitting a Stage 2 modwise kit!

[GreenV8S]

I had sort of similar symptoms when the fuel pressure was too high, it would run but on the point of flooding and could easily be provoked into a rich misfire. Once it had warmed up and the ECU leaned the mixture out, it drove fine. So I suggest you check the coolant temp sender used by the ECU to make sure it's giving the ECU a sensible answer, and then if nothing's wrong there check the fuel pressure.

[Chim_Pete]

GreenV8S said:

I had sort of similar symptoms when the fuel pressure was too high, it would run but on the point of flooding and could easily be provoked into a rich misfire. Once it had warmed up and the ECU leaned the mixture out, it drove fine. So I suggest you check the coolant temp sender used by the ECU to make sure it's giving the ECU a sensible answer, and then if nothing's wrong there check the fuel pressure.

Thanks - I will start with checking the temp sender like you say.

Cheers.

[MADMAX2]

Chim_Pete said:

Hey all,

Done a search but could find any similar probs to this...

In ambient temperatures below ~10degC my chim starts fine but isn't very happy until after about 4-5mins of stationary warm up time. When you gently touch the throttle the revs die instead of rising, but if you poke the throttle you can blip the revs and then hold it at a fast idle. Then after about 3-5mins (depending on how cold it is) something must change, i.e. a sensor value or valve or something because then it responds normally. If it is left idleing you can hear a subtle change in the engine noise when this happens - I haven't put my finger on how to describe this yet...

Also if you stall it during this warm-up time, it won't want to restart for at least 5mins (I don't know if this is related or not).

I have been told once that "they do that sir", but something can't be right in my opinion.

Any tips on things to check/try gratefully recieved.

Cheers,

Pete.
1995 Chim 400

Pete when you start the car cold and get this revs problem does the revs suddenly pick up after about a minute or two to around 1400rpm-ish then steady back down when the ecu corrects?

[Chim_Pete]

Hi MADMAX2,

No - doesn't do that, the idle is perfectly smooth.

Cheers.

[SMB]

I have a 95 400 too. And used to have a similar though less severe issue. Would always start but was clearly rough and on gentle throttle revs die away until engine settles down, took about 2-3 mins on mine to go completely , but was driveable.

On the advice of a friend with a slightly newer 400 I got an updated standard TVR map for the ECU, and it worked, still starts on the button, but now both hot and cold much smoother than before. Cost was less than £100 for a new map delivered. Production cost probably no more than £5, but it has made my car smoother.

[Chim_Pete]

Hi SMB,

That's interesting to know. Mine is also driveable straight away, it just means you have to slip the clutch lots when pulling away because of using more engine revs-think thats what finished off my old clutch, so now I just wait a couple of mins...

Cheers.

Edited by Chim_Pete on Wednesday 12th November 10:47

[blitzracing]

Just a thought. The on initial start up, the ecu relies on the fixed part of the fuel mapping until the lambda probes get hot, and can run very rich, and as green says the temp sendor will make a big difference. However after about 20 -25 seconds the lambda probes get hot as they have their own 12 volt heaters, and the mixture should then correct itself for optimum running. If you lost the heater supply it can take some minutes for the probes to start working and the car will continue to run rich. It would seem an odd fault however, as its the same supply as runs the fuel pump, and thats pretty obvious if its missing, but if you want to check its the red wire going to the probe. It should be at 12volts when the engine is running only. Its also possible one probe has failed, and the ECU is in fall back mode, and this would show up on a fault code reader. One thing of note is you do hear the engine note change as the probes get hot.

Mark

[Chim_Pete]

Thanks for the input Mark - another good prognosis.

I didn't realise they were heated lambdas - I will definately check they are getting their correct supply. Sounds perhaps unlikely like you say (re:the fuel pump) but definately worth a look.

Cheers.