Lump idle + throttle response when cold?

MikeV8SE said:

OK, it's been pretty cold lately and the RR has been stood for a few days, so I imagine a "deep chill" has set in! Anyway, when I start it up it starts OK (couple of turns, but then it is cold!) and idles OK, if a little lumpy.

However, when I go to accelerate the revs dip, almost to the point of stalling, before picking up. Also, if I give it a rev and let the revs come back down, they fall below the normal idle speed, again almost to the point of staklling, then come back to idle fine. As soon as it's warmed up (aided by the cardboard over the radiator!) it's fine.

Now, this only happens when it's really cold. I'm gonna clean the MAF this weekend (I'm told a bit of brake or carb cleaner is ideal?) and also change the air filter for a K&N replacement next week as the stock item looks filthy! Will this help or should I be looking elsewhere for a solution? TPS maybe?

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wammers said:

Sounds pretty normal. Freezing cold engines never run well it's a fact of life. If the filter is filthy and clogged up i would be bloody amazed if it did not help.

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MikeV8SE said:

Stepper? EFi sensor??

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MirfieldPete said:

Stepper motor is on the idle air bypass valve on the rear of the air intake plenum. It occasionally sticks and can be removed (using 5.5mm allen key iirc) and freed off with a little spray of WD40. EFI coolant temperature sensor is at the front top of the engine, close to the dizzy cap. The fuel injection ECU adjusts the mixture depending on the engine temperature indicated by the sensor. You can get a replacement ETC8496 for less than a tenner.

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MirfieldPete said:

Stepper motor is on the idle air bypass valve on the rear of the air intake plenum. It occasionally sticks and can be removed (using 5.5mm allen key iirc) and freed off with a little spray of WD40. EFI coolant temperature sensor is at the front top of the engine, close to the dizzy cap. The fuel injection ECU adjusts the mixture depending on the engine temperature indicated by the sensor. You can get a replacement ETC8496 for less than a tenner.

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MirfieldPete said:

Have you checked the EFI temperature sensor?

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MikeV8SE said:

OK, it's been pretty cold lately and the RR has been stood for a few days, so I imagine a "deep chill" has set in! Anyway, when I start it up it starts OK (couple of turns, but then it is cold!) and idles OK, if a little lumpy.

However, when I go to accelerate the revs dip, almost to the point of stalling, before picking up. Also, if I give it a rev and let the revs come back down, they fall below the normal idle speed, again almost to the point of staklling, then come back to idle fine. As soon as it's warmed up (aided by the cardboard over the radiator!) it's fine.

Now, this only happens when it's really cold.

Yeah, they do that. It sounds fine LEAVE IT ALONE. In any event, I would be inclined to maybe check ignition timing and VAC advance if it is bogging down on acceleration then nearly stalling idling down but I'm sure you'd know if you had a timing problem.

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classic kev said:

Yeah, they do that. It sounds fine LEAVE IT ALONE. In any event, I would be inclined to maybe check ignition timing and VAC advance if it is bogging down on acceleration then nearly stalling idling down but I'm sure you'd know if you had a timing problem.

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MikeV8SE said:

Thing is, as it's been sat for 4 years it needs a bit of TLC to get it running sweet again. Oil is fine, coolant been changed - just working my way round the car, so new air filter and cleaning the MAF sensor is next! Looks to have a new dizzy and leads so that's good, haven't checked the spark plugs yet but got no reason to think they're anything but good.

Will give the stepper and EFI temp sensors a check over this weekend too.

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