3000RPM Idling Problem

[Sheriff69]

Here’s one of those annoying problems that we all face time to time with owning a car!

The car in question is a 2002 VY Commodore S Pack Ute, dual fuel, 5 speed manual.

It’s recently had an 180,000km service. The gas system (which is non Holden standard) has also been serviced a few months ago. New spark plugs were fitted during the 180,000km service along with your normal oils and filters.

The problem is that in the morning after start up on (on Gas at this stage) and only driving about 3km the car will idle at 3000rpm whilst in neutral at the traffic lights or a stop sign. You drive to a safe distance, pull over and turn the engine off, wait about 10 seconds and restart the engine with no problems – the car is now idling normally. In the afternoon when you drive back home the car doesn’t play up at all and behaves normally all the way home which is about a 40-50 minute drive. Five to seven days can pass before it will play up again as described above. Recently the car has played up all the time with switching the engine off and restarting it NOT fixing the problem.

We’ve had the Ute checked by an independent mechanic who attached the Tech 2 device into the car’s computer with no faults recorded. We’ve then taken it to a Holden dealer; they attached the Tech 2 to the car’s computer with a Low Voltage fault within the Fuel Injection System. According to Holden they required the car for a day to do further testing on the cars computers in an effort to try and isolate the problem, but the dealer being honest with me said that he didn’t want to do that at this stage as he would have to charge me a few hundred bucks with no possible answers.

Since the visit to Holden I have now flicked the cars fuel source over to petrol with no faults for the last 4 days. Next week I’ll be flicking it back over to gas to see whether the fault is either Gas related or Petrol related. At this stage it isn’t Petrol related.

When the fault occurs there are no engine fault lights illuminated on the dash to indicate a faulty sensor or other which I believe when running on gas it won’t do as the gas system is non standard, can anyone confirm that this would be the case please?

So I’m putting this annoying fault out there for anyone to try and help me with the cause of this problem. Any help or advice in fixing this fault would be greatly appreciated as no one at this stage can help me.

Thanking you all in advanced for your time.

[strgas]

the low voltage reading will always be there because the injector voltage is turned off when running on gas simple fix for that is to return power back to the PCM without supplying power back to the injectors (done plenty of these in the past ) What gas system are you running ?? who fitted the new plugs and what type where they and what gap ??

[strgas]

Was the gas system dyno tuned or tuned on board ???

[Sheriff69]

Thanx for your speedy response strgas!

I'm not sure exactly what gas system the car has, maybe you can tell me what sort of systems are out there in an effort to tell you which one we have?

In relation to the Spark Plugs the car is fitted with NGK BP6EFS-13 which has a 1.3mm gap.

In relation to the gas system being Dyno Tuned or Tuned on board I'm lead to believe the gas servise place Dyno Tuned it but they could just be saying that.

[strgas]

ok plug choice is good 1.0 mm would be my gap setting . as to the makes of gas systems there are so many on the market , which company fitted the system for you ?

[Sheriff69]

The company that fitted the system are called LPG Coversions in Freight Rd Tullamarine, Melbourne.

[Sheriff69]

You'll have to excuse me strgas as I have to sign off now, I have a 4am start tomorrow with work.

Please let me know what you think could be causing this problem as I'm keen to fix it asap.

I'll sign back on tomorrow night to check the progress of this forum.

Cheers : )

[greenacc]

I had a similar problem wit my VS. From memory is was the TPS, but i don't have gas so don't know if it is relevent to you.

[WogBoyz]

TPS? i though it woulda been more of a IAC problem as that controls the idle

[Sheriff69]

I too thought it may be the Throttle Position Sensor or the Idle Air Control valve.

The IAC valve was replaced back in May this year after I pulled it apart to clean and was unable to put it back together! That excercise cost me around $75!

As far as the TPS sensor is concerned I've been told that if it was faulty whilst the car is running on petrol then it would send a fault signal to the computer thus illuminating the engine warning light on the instrument panel. This is yet to occur should the TPS sensor be at fault.

Any other ideas?

[strgas]

i have found in the past that most gas fitters are lazy and dont follow instructions to well and take a short cut by running the LPG processor earth wire to a body earth using a tek screw this in time can become a point of high resistance and a poor earth connection is now the cause of the problem as this will now force the power in the processor to seek another point of earth and can put voltage back thru the O2 sensor wire giving higher voltage readings , TPS voltage can be higher up to 12 volts depending on the resistance at the dodgy earth wire , can be intermittent at times when the car hits a bump and knocks the earth connection and it makes contact once again till such time as the resistance builds back up again , Im not saying this is your problem to the letter just a common problem i see most days , some systems can run with their processor disconnected altogether and may never have a problem plug it back in and the problem soon comes back . intermittent faults are the hardest one to find or even reproduce in the workshop .

[Sheriff69]

OK, the wife has just texted me with news that the car is playing up again! Seems to only do it when she's driving it cos I cant get it to do it!

Now the car is running on Petrol this time so we can now confirm that it does it on both fuel sources, LPG and Petrol.

When the car played up there was no engine warning light on the dash.

Are we getting closer to the problem now that we know it happens on both fuel sources or has this now made this problem more complicated?

Thanx for your advice strgas, totally agree with you on intermitant faults and not being able to reproduce them in a workshop environment. What do you now think?

[strgas]

your problem may be a result of a burnt out wire , dodgy connection or poor workmanship and now is present on both fuels given time the fault may become bad enough to stop the car running altogether .

[Sheriff69]

Oh great, the wife will be real happy then!

Do you think the problem could be computer related?

[strgas]

hard to say from behind the keyboard could be related to the ecm or just dodgy workmanship or part related ,

[Sheriff69]

OK, appreciate that. I'm going to PM you strgas to see whether your able to give us some further assistance.

Many thanx for your time in answering my questions.

If anyone else has had this problem then I sure would like to hear from you, please!!!

[strgas]

ok no worries

[Sheriff69]

strgas

PM sent.

Cheers mate : )

[Sheriff69]

Here we go again!

The wife has just dragged me out of bed to hear for the first time the car revving ta 2500rpm and not 3000rpm as first stated. I popped the bonnet and checked the throttle cable and the cruise control cable, both were slack and under no tension.

Electrically I wiggled every electrical connector I could from under the bonnet with no change in RPM. I checked the dash for any warning lights as the car is still on Petrol and there were no dash lights to indicate any problems.

I turned the engine off, waited 10 seconds and restarted the engine. The engine then revved at around 1500rpm, gave the throttle a quick 'squirt' and it then began to idle normally.

Apart from taking the car to an Auto Elec to look at does anyone have any other thoughts on what could be causing this?

Cheers

[VesperZ]

From memory the gas system uses a "piggy-back" ECU and uses that to control your gas system. If your car is running fine on Petrol then that pretty well isolates your issue to your gas system and it may very well be your gas piggy-back system causing the issue. The other thing is you should probably not be starting your car on gas as you really need to be running gas on a warm engine, not a cold one. But that is the extent of my knowledge with gas systems.

[VesperZ]

From memory the gas system uses a "piggy-back" ECU and uses that to control your gas system. If your car is running fine on Petrol then that pretty well isolates your issue to your gas system and it may very well be your gas piggy-back system causing the issue. The other thing is you should probably not be starting your car on gas as you really need to be running gas on a warm engine, not a cold one. But that is the extent of my knowledge with gas systems.

Sorry my bad, just realised it happens on both gas and petrol. I would assume it's your TPS or a fault with the signal sent back from the TPS to your ECU

[Sheriff69]

Thankyou H0LD3N for your comments.

I've rung the mechanic today and have reported my experience with the car. The car is going back to them for a few days this time so that they can do further testing. I like you are thinking it is a sensor of some sort or the engines computer BUT the engine warning light does not come on at any time when the engine plays up. My knowledge is that should there be a problem with the engine whilst on petrol then the engines computer will log a fault and turn the engine warning light on, this is just not happening.

Oh by the way, the wife still wants to sell the car even though I'm saying no!

I'm not experiencing a 'happy wife happy life' right now so anyone with the same experience as I would be of a HUGE help about now!

[Sheriff69]

It would appear that the problem has now been fixed thanks to the guys at VP Auto Care in Tullamarine,Melbourne.

After having the car for three days the boys isolated the problem down to a faulty TPS sensor which they had to replace twice! The first sensor did fix the high revving problem but then gave us a engine warning light on the dash. The second sensor took the warning light away and we now are not experiencing the high revving problem on either fuel sources.

Thanks to everyone for their imput, much appreciated.