I have a 96 XJR6 with 170,000km, Car has been parked for about half year, was running perfectly before parked. I got it out of the storage couple of days ago, and did an oil change on it immediately. Was using 10W40 before but decided to go 20W50 this time to see if it gets rid of the chain noise at startup and it did just that.

Now for the fun stuff, the car exhibit the following symptom
-Rough Idle ( Not rough like misfire, but you do notice and feel the slight shake the engine produce every few second, when driving i do not notice anything wrong, you would feel the slight shake only when idling in gear or not ) The Rough Idle happens when car is cold and hot.


-Stalling at intersection/red light (At first it was only the rough idle, but today it totally stalled on me at intersection, I was able to fire car right back up, but it will stall again if the engine is revved )

-Stalling right after startup (After the continuous stalling i had to pull the car over to the side of the road, tried turning the car off and starting it again, it cranks and turns over and dies instantly, the only way to keep car running is revving the engine.)

Here is what i did

-Checked For Code (No Code Found)
-Checked All Coils (Night time with cardboard covering each coil)
-Replaced all plugs while i was in there

I did some reading and realize that MAF sensor and ECT sensor is crucial when it comes the whole ignition stuff, after playing around I was able to start the car without any problem with ECT sensor disconnected, with the sensor connected when the car is hot it would NOT stay running unless revved.

While the car is running without ECT sensor connected, if i disconnect MAF sensor while the car is running, the idle instantly becomes smoother, I was able to drive the car normally without any issue.

-Scan Tool Indicate
ECT Sensor : 79-81c when connected with the car idling
MAF flow rate : 0.05 g/s this value does increase when the car is driving.
Short Term Fuel Trim 24.2%
Long Term Fuel Trim 3.9%

With MAF Disconnected
Short Term Fuel Trim -25%
Long Term 3.9%

It seems like every sensor is going its job, but somehow or something is wrong... any idea would be appreciated! thank you so much for taking the time to read my problem!

 

Your STFT indicates weak mixture. I would check for air leaks first. Spray "EasyStart" around Throttle, inlet manifold and any other air and vac pipes. If you get a slight increase in revs then you have a leak.

Also see if you can monitor O2 sensors switching with your scan tool.

 

Im assumming easystart is the same as starting fluid yes? can this be done with carb cleaner as well? is there a vac diagram anywhere? i dont see one on the hood.

As for the o2 sensor, i can see voltage change with the scantool, is that the switching you are referring to?

Thank you so much for your response

 

Yes starting fluid. I've heard of people using all sorts of things but I've always used "EasyStart" which is a UK brand - cheap, plentiful and easy to use.

There isn't much of a vac system on the X300 (at least in UK) so don't worry about a diagram. Just hit every pipe you see.

 

[QUOTE=b1mcp;1433758]Yes starting fluid. I've heard of people using all sorts of things but I've always used "EasyStart" which is a UK brand - cheap, plentiful and easy to use.
There's another version of "EasyStart" called "Startya*******". I'm sure it's the same stuff, it just raises a smile every time you reach for it.

I see the word has been redacted. Shakespeare uses it in his plays though. Ba***rd.

 

I thought you were winding me up but I googled it. Fantastic.

Must come from the same family as "Sticks Like Sh*t" adhesive (genuine made by Evostick).

Anyway, we digress...

 

Just to attempt to complete this discussion, but on a less entertaining level, carb cleaner will not only not assist in starting, it will prevent it.

 

Ummm but in theory it would find me the vac leak i was looking for no?

 

Yeah, just look for a decrease in revs instead of an increase. When you spray the leak, you'll be replacing oxygen, which your engine is happy to burn, with carb-cleaner, which it isn't so happy to burn.
With starting fluid you replace oxygen (burns happily when combined with fuel) with a volatile fuel source (burns lustily given that plenty of oxygen is available through the normal, filtered intake air path

 

Update:
I cleaned the MAF sensor, it still seems to want to stall. Now here is the interesting thing, say if it stalls and i try to crank and it would turn over and stall again, but with ECT sensor disconnected it would crank for a period of time and then turn over and stay running, almost feels like it ran out of gas before? With ECT disconnected, ECU reads -40c and will dump loads of fuel inside the cylinder maybe thats why it kept it running? thoughts anyone?

 

Could be either low fuel pressure or fuel starvation. Change the fuel filter and maybe also check the air filter? Maybe a squirrel built a nest in the intake over the winter?

 

air filter is good, fuel pressure i will have to get an gauge to check, but if its indeed bad fuel filter, how would it idle fine with ect disconnected?

 

Here is the theory. EasyStart is fuel. It's a very good fuel for spraying into the carb air intake to get a cold engine to fire. It's ether. You can actually run an engine just by spraying EasyStart into the carb even if you're out of petrol.

Now for the bit our friend is suggesting. Any air leak into the intake will dilute the air fuel ratio and the engine will struggle. Filling that leaking air with EasyStart will add much needed fuel to the air and the engine will rev up a bit.

If this happens you know the EasyStart has been sucked in through whatever vacuum leak.

I have never heard of this method before but I can see what's happening.

Also I was going to add that your problem is fuel not spark. More precisely air fuel ratio AFR.

 

Update:
New Coolant Sensor in, Did not solve the rough idle problem.
Seeing STFT is 24% at idle but while keep rev around 1500 rpm for 30 second, it goes down to 4-11% it leads me to believe there is indeed an vacuum leak, because all the hose are so well hidden beneath the intercooler/supercharger i decided to take everything apart, while i'm at it i will clean the tb

 

If I had to take a wild guess, check the vacuum powered air bypass on the supercharger to make sure it is not stuck. And check that pipe between the throttle body and air intake, it may have developed a crack and is impossible to see from the top of the engine.

 

Update:
In process of checking every vac hose for leak, found out that lower air duct hose had a tear, not sure if that would cause the rough idle.







On another intersting note, my throttle body is spotless! i heard that usually it should be gunked up no?

 

I put black duct tape on the cold air pipe of our Fiat Panda, it did have a dead spot at 4000rpm in 1st gear where the engine lost all power. Now it's fine. I think air leaking in the sides of an intake pipe really spoils smooth running.

 

Update:
Found another spot that might have a leak, the cartridge on the manifold and the vac line that leads to the brake servo looks kinda fishy so i will replace both while im at it.

 

Update:
New lower Airduct hose in, New cartridge for Intake manifold leading to brake servo, New inlet manifold gasket, replaced all ignition coils rechecked every hose for vac leak. Unfortunately problem still persist, rough idle and stall still there. STFT still indicates 24.5% when warm. I need some idea guys this car is killing me here

 

Can you measure the manifold vacuum at idle? Then you might be able to rule out a vacuum leak. My VDP idled with 15" Hg at 3500' elevation. I'd expect more at sea level.

I wonder if your fuel pressure regulator is bad? I had similar symptoms on another car and it was low fuel pressure. At least that is easy to change!