Rough engine start/stop

Some years ago I heard that LPG conversion results in higher temperatures and affects the valves (wear).
You could check their function, too (travel, compression,...)

 

I think they're called intake valves and exhaust valves.
If there's too much wear at their necks and/or at their gasket surface maybe they cannot open/close properly or they would have a bad timing.
The high temperatures of LPG combustion can heat up the valves. The exhaust valves more than the intake valves, because the intake valves have fresh air while the exhaust valves have only hot exhaust gases.
The hotter exhaust valve can possibly be bonded in the gasket area and break free by force of the camshaft again and again, wearing the gasket surface.
This could influence the engine (compression and expansion ratio) with Atkinson Miller cycle much more than a standard Otto engine at least running at lower rpm and while starting.

 

Reset the ECU start to drive with cold engine and with just gasoline and monitor the fuel trim values (or just short term fuel trim). They should stay within + or – 10%.

If it works fine then you probably have some problem with LPG conversion that will mix up the fuel trim values so the problem also exists while running with gasoline. You getting a code for running lean on long drives would also indicate this.

If the fuel trims stay outside of that + or – 10% you should be able to just normal diagnosing methods for rich or lean running. This includes the engine damage that MickyMatter already suggested. Anyways keep us posted. And if you can put the fuel trim numbers that you get here so that we can look at them.

 

You need to reset the ECU before doing the test! You can reset the ECU by just disconnecting the 12V battery for 5min.

Monitor the short term fuel trim (bank1) and long term fuel trim (also bank1).

But as a test just driving it should be fine. If it works normally on gasoline after reset then the fault is in LPG system. Just keep it off LPG until this is figured out or reset it if you have driven on LPG and want to continue diagnosing.

If the LPG system has problem or is just adjusted/installed wrong when running on LPG it will be pulling the long term fuel trim to wrong value. And then when running on gasoline that wrong value will be slowly corrected.

Or of course it can also be something totally different. But then you would have bad fuel trim numbers while doing the test. And from those numbers you can figure out where the problem is.

 

What is the odometer reading?

Did you thoroughly clean the corrosion around the throttle body opening on the intake manifold which was evident in your photo? You do not need any air leaks between the throttle body and the intake manifold.

I am wondering if you have an engine air intake leak somewhere downstream from the MAF sensor which is allowing excess air to enter the system, thus causing the P0171 code. Maybe after the engine heats up, the leak goes away because a marginal gasket starts to seal again...

 

I hate to say it but rough starts (some times so rough that it rock the entire car back/forth while in P) and stops was an operating condition before my hybrid battery failed. Repairing the battery improved it a lot. Later on after several battery repairs, the battery was replaced with a new Toyota pack and the throttle body and MAF were cleaned at that time too. Symptoms are gone. So which fixed it? Or was a combination of the two?

 

I suspect fuel trim also. The engine when cold has more fuel added as warm up routine to combat the exact situation you describe. Lean condition on cold engine is not good. This is confirmed by the lean condition code thrown.

Surprised your not seeing more codes. Fuel trim monitoring and resolution is very complicated many sensors
And tied into engine temp. Take it easy on the engine your running lean engine will run good but hot.

How many miles? Did this event happen fast? Maybe poor fuel? Fuel pressure?

 

Did you clear the ECU?

The numbers look good enough. It did never go into negatives? If it stays between 0 and +7% that’s good enough.

Did the problem still exist or did it stop?

 

As the combined fuel trim newer went above +7% there really can’t be bad enough vacuum leak (like leak in that throttle body to manifold gasket). So problem is somewhere else.

You haven’t gotten any other fault codes except that P0171? How good is your HV-battery?

You could do the compression test. You need a normal compression tester and a computer with Techstream (Mini-VCI is cheap way to get it).

 

P0171 code only shows with LPG? If yes then next time you use LPG monitor the fuel trim numbers. If combined fuel trim goes outside of that + or – 10% (or maybe outside of 0 to +15% if you already have 7% with gasoline) there’s something wrong with LPG system.

That possible problem with LPG system may or may not be related with this engine shake at starts and stops with cold engine. But a problem that causes engine to run lean can cause damage to engine.

 

No with car off you turn the butterfly by hand. Lubricate the spring on the end.

Btw, there's a sneaky throat clamp under the air cleaner box that keeps the box tight to the throttle body Its a 10mm hose clamp. It must be tight or you will have alot of unmetered air sneaking in the throttle body. You really cant see it you have to do it by feel I seem to remember.