Thread: Erratic revs at start up

I had similar problems with mine but not as bad as you describe - hunting up and down instead of idling steadily, with the occasional stall.

I changed the Idle Air Control valve which improved things marginally but the idle was still erratic when hot.

Two weeks ago I tried the Cost Effective Maintenance Fuel Treatment after reading about it on this forum and it has totally transformed the car after just half a tank of fuel! It idles beautifully; runs much more smoothly; doesn't pop on the overrun; sounds quieter at all speeds; doesn't have the awful hesitation when accelerating from cold and is now a delight to drive. All of these symptoms I now put down to injectors not spraying properly.

It may be the same case with your car,

Cheers Charlie

I'm running a V8 petrol, I thought this was for diesels.

I have been running LPG for 2 years, I was under the impression that would have kept the injectors clean?

I have been running LPG for 2 years, I was under the impression that would have kept the injectors clean?

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Au contraire, only occasional use of the injectors can cause them to seize, as a member in Victoria discovered and I sold him my injectors.

I would look at your ECU temperature sensor. It may not be reading correctly but on reflection perhaps it is partially seized injectors.
Try some sort of injector cleaner first and run a full tank through.
Regard sPhilip A

Thanks PhilipA - I was wondering about the ECU temp sensor as is really only started the last couple of weeks when the air temp as dropped.

I just came back from a drive and the air temp was the lowest so far and the starting was the worst with the worst throttle response so far. Which became much more tolerable when the engine warmed up.

Seemed to be running OKish on Petrol so tried gas, same no difference.

Filled up with petrol, started the car on gas and all OK.

Went to a different station, filled up with gas. Started on gas and not happy at all, flicked back to petrol and was OKish again.

When under load its fine. When coasting off the throttle (in heavy traffic / approaching traffic lights) the revs are hunting, not a lot like it was before I replaced the MAF and stepper motor, but they are no longer constant.

So running temperature makes a difference, and I have the same rev hunting on both petrol and gas (more noticeable on gas).

How can I check if it is the ECU temperature sensor, and where is it?

silly question time:

is the ECU temp sensor the same as the coolant temp sensor?

If it is, I replaced it about 18 months ago....

So running temperature makes a difference, and I have the same rev hunting on both petrol and gas (more noticeable on gas).

How can I check if it is the ECU temperature sensor, and where is it?

Do you have a gas injection system which times from the ECU/injectors? If not it cannot be the injection causing the problem.

The ECU temp sensor is the one on top of the inlet manifold at the RH front with an injector plug and 2 wires.
I would also look at air leaks in the inlet manifold, where all hoses terminate and maybe the bolts mounting the IAC plate at the back.

Regards Philip A

Originally Posted by PhilipA

Do you have a gas injection system which times from the ECU/injectors? If not it cannot be the injection causing the problem.

Regards Philip A

Thanks again Philip, I'll check the hose connections and check for inlet manifold leeks.

I have asked many people about my injection system (including the importer) and no one has been able to give me an answer about where the the gas gets its timing from. They all say "the gas injectors work off the gas map" no one has been able to tell me if it is slaved to the ECU.

One of the reasons I asked this question was that I got the disco chipped and wanted to know if it would effect the gas

Originally Posted by black betty

I have asked many people about my injection system (including the importer) and no one has been able to give me an answer about where the the gas gets its timing from. They all say "the gas injectors work off the gas map" no one has been able to tell me if it is slaved to the ECU.

One of the reasons I asked this question was that I got the disco chipped and wanted to know if it would effect the gas

Gas injection times are calculated from the petrol injector on-time (read directly from the vehicle ECU via the original injector wires) and the RPM. The conversion numbers form a 2 dimensional "map" so any variation in the petrol injector on-time will vary the gas injection. If the chip you fitted varies the petrol injector time then your "map" will need readjusting to bring the gas fuelling back in line.

Any errors in petrol fuelling will be translated into gas errors, so make sure you are 100% happy with the petrol before getting gas times reset.

The gas ecu does not change ignition timing, only the vehicle ECU does that, the knock sensor will allow extra advance if applicable for the higher octane fuel.