GQ TB42 dual fuel - rough idle on LPG - troubleshooting help

Hi guys,

some of you have have seen my previous thread about my vacuum line confusion. Now I've sorted out my vacuum lines and im still being bugged by a mysterious rough idle on gas. I'll try to keep it as short as possible. Would definitely appreciate any comments on this one.

So - was servicing the new Mav, took off the air filter box to get to the spark plugs and there was one vacuum line that I ripped off as I didn't see it first.

Ever since then, my idle on gas drops down to 300 or so and the engine eventually carks it if I leave it there. Funny thing is, apart from the idling issue, the car runs very smoothly on LPG. Idle on petrol is however at 1100! Both idles were fine before I popped this vacuum line.

Here's what I've done so far.

*Fitted the correct NGK plugs (previous owner had a couple of different ones in there :mad:) and spiral core leads. Runs much much better now. But idle problem persisted.
*Replaced all vacuum lines from carby to air filter box. Confirmed that all lines are going where they should be.
*Replaced air filter and petrol fuel filter
*Also waiting on the pertronix kit to come in from the US, with a coil to suit. Will also get my rotor button extended.

Haven't checked the timing yet - don't have a timing light on hand, but it seems to be ok from what I can judge!

As all this started occurring after I had popped off the vacuum line I thought it must come down to a vacuum line... but obviously something else is going on here. Short of going to a gas mob and shelling out $$$, i'd appreciate any troubleshooting tips here. I've read up a bit on solutions to similar problems, but the high idle on petrol and low idle on gas doesn't seem related.

happy trollin'!!

Nick

I think you might still have a vacumn leak somewhere Nick, if its suckin in air it will affect the fuel air mixture. Can you hear any whistlin noise?
It might also be why its idling fast on petrol.

Quote:

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Originally Posted by Stumpjumper

I think you might still have a vacumn leak somewhere Nick, if its suckin in air it will affect the fuel air mixture. Can you hear any whistlin noise?
It might also be why its idling fast on petrol.

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Agreed...... It still sounds like vacuum leak somewhere.

With the engine running, slowly go over all your vacuum lines with some WD40 or CRC one by one, from end to end (most important to go slowly & do one at a time), then in & around where there connected too.

If at any time the idle changes you've found your leak.

If you wait a few seconds the Idle will return to what it was, at this point spay the area that you got the response from again to confirm & if your on the money fix the leak.

If your successful here im tipping your problem will be solved.

Thanks guys, I'll get on to it tomorrow and let you know. Would be great to have all the wobblies ironed out!

Hi,

I've read through on your issue with the LPG irregular idle, etc. I have the exact problem on hand. \

Have you managed to sort out your problem and if yes can you please advice me on what to do?

I have a 1998 GU-Ti 4500 (LPG/Petrol)

Regards
AG

Hi All,

O2 sensor was the problem....replaced and mixture set up by LPG pro today.....$200-00.

Drives like a dream.

Tx All for assisting with advise.

Regards

AG