LPG 1fz-fe idle problem while driving (1 Viewer)

[DesFZ80]

Hey guys, first post here so excuse me if I have gone about this the wrong way.

I’ve been having an issue when running on LPG, when I’m driving the idle tends to remain far above where it should. As I change gears and press the clutch, the revs remain almost where they were before I let off the accelerator. Best described it feels like a “sticky” throttle pedal. If I change gear at 2000rpm the revs stay at around 1600, or if I change at 3500 they might stay at 3000, just some examples so you see the problem. The revs do go back down if I wait a few seconds and the problem goes away when I change to petrol. Also, when starting up on LPG it revs up and then immediately drops to 200rpm and then idles at 1600rpm (when cold) until it warms up and resumes a normal idle

As you can imagine it leads to very poor gear changes and I’m worried it will damage the transmission so have tried to avoid using gas now.

I would very much appreciate any input from anyone who knows what the problem could be or anyone who has had a similar problem.

Thanks in advance

 

[junior80]

probably wont get too many replies here on the subject of lpg related issues unfortunately. whats your gas system?

 

[DesFZ80]

Sorry I’m not too knowledgeable on gas, when you ask what gas system I have are you referring to injected or another kind. I know it’s not injected but don’t know much more about it than that. Thanks for your reply

 

[SmokingRocks]

What year and engine do you have?

 

[DesFZ80]

It’s a 94 1fz fe

 

[SmokingRocks]

Outfitted with an LPG conversion? And a 5 speed manual box?

Australian spec 1fz-fe's didn't come with OBD 1, did they? The first step is always to pull check engine codes if you can.

Have your replaced your throttle cable? If so it must be a toyota OEM cable, the aftermarket cables stick even though they are brand new. I would have a friend rev the engine from inside the cab while you inspect the throttle body, verify that the throttle returns all the way to the closed position.

 

[DesFZ80]

Yes it’s a manual and lpg conversion. My first thought was the throttle cable however I don’t know why it would not do the same on petrol if that was the case. It runs perfectly on petrol. Do you know if there are any lpg specific sensors which could cause such a problem?

 

[SmokingRocks]

my knowledge in the LPG conversion world is nill, sorry. I would surmise that it is due to an injector issue that is causing the air-fuel mixture to get wonky. Your initial post is confusing though, you constantly refer to having an issue when running on gas but when you switch to petrol the problem goes away.

In the US gas is what we commonly call petrol, so I just want to make sure we understand that when you say gas you meant LPG.

 

[DesFZ80]

Oh sorry, My mistake for calling it gas not LPG, I didn’t quite think of that. Thanks for your help anyway, much appreciated

 

[thelal]

was there any recent repairs or work on the engine, wiring etc. My first look would be at all connectors and wiring for the LPG.
You will need to check what model of LPG you have (post pics of ECU, filters, water heater etc.)
I run LPG on my 97 w/o any issues and LPG on prev 96 petrol.
You will likely have a better response on a more local (Aussie) forum where those guys are running LPG

 

[Desert Dino]

1FZ-FE and LPG bad combination will not last

 

[thelal]

1FZ-FE and LPG bad combination will not last

any evidence on that for 5th generation (direct injection) systems. Seem to be plenty of long running engines in Aussie on LPG