Hi,

Looking for some advice on a weird issue I have.
I will preface this by saying I am getting no codes whatsoever, the engine management light does not come on and I do not go into restricted performance.

When starting the engine, it will sound fine and then when the revs settle, I start to get a stumble and the engine will sometimes shake. It will drive fine and as soon as it goes above 1500rpm the stumble will go away with no noticeable loss in performance. As soon as the car is to temperature, it will behave and perform as normal even at idle.

I cant see any wetness in the spark plug wells and no noticeable vacuum leaks.

I have been driving the car to see if I can get any codes to show, but not happened so far.

Any advice?

Cheers,

Ryan

 

If you have an ODB reader which can monitor live data you should be able to monitor the fuel trims, engine modes and misfires whilst the engine is misbehaving, although I am surprised that no stored or pending codes are showing.

As a wild guess, it sounds as if the engine is running in open loop mode until the engine is hot. The obvious issue would be an O2 sensor problem but I don't understand why this would not record a fault. Is your ODB reader a good quality one which is X100 compatible? This is an old engine/ODB design and some readers might struggle to provide a proper reading.

Richard

 

I'm also surprised by no codes being present. I have a foxwell NT301 which has been reliable for my Dad's X358. It does ask for the Vin on startup and recognises it is reading from a X100.

I'm pretty sure it does read live data from what I can recall, so will be looking into that when I next have a chance.

Cheers!

 

I went to visit my parents today, but Dad has misplaced the reader I usually use, so this is from a bluetooth reader.

According to live data, the poor idle is happening in closed loop

Interestingly at idle I am getting quite a high % on STF trim bank 1 and negative on bank 2.
When I rev the car a little, the misfire goes and fuel trim looks somewhat better.




I forgot to look at the voltages for the upstream O2 sensors whilst I was testing, so will be doing that tomorrow.

 

The high fuel trim at idle on bank 1 does seem odd. Maybe check for leaks in the intake ducting and clean the MAF with some spray? It's running closed loop so that is probably why you are getting no 02 sensor faults

Richard

 

Looks like an air leak on bank 1.

 

Heard a slight hissing from the PCV so had cleaned that as per instructions on the forum and replaced the O rings. It seems to seal a lot nicer compared to when it came off initially.

Values for the O2 sensors seem to be fine from what I can see.

Interestingly after changing the O rings, I finally got a code flash up for a second and then went away.
P0303, so looks like I have something to chase now!

 

I agree that the O2 sensors look OK.

Is the problem still there after the O-ring replacement? As you say, a misfire on 3 could be spark plug, coil pack etc so these are things you can easily check with a multimeter, by swapping components or by substitution.

Richard

 

It is still there, but soon goes away when the engine warms up a little. The problem I have is the code flashed up, but as soon as the engine was turned off and driven again I couldnt get the code to come back on and no misfire.
I suspect I will have the misfire again when starting from completely cold, but I at least have a cylinder to investigate now!

 

I would pour a 20-ounce bottle of Techron down the fuel filler hatch as a cheap-and-easy next step....

 

I had put a can of BG44K in on my last full tank when I noticed the misfire and hadn't changed much at the time.
Would you recommend techron over BG?

I havent used fuel additives at all before this, but saw BG recommended a few times in forum posts.

 

BG44K and Techron are the two most effective fuel injection system cleaners available. My guess is that if you obtained no improvement with BG44K, Techron may not make any difference either....

 

If you have not done so already, thoroughly inspect the accordion section of your plastic air duct tube for splits and cracks. You may need to remove it in order to check both its top side and bottom side. As these plastic air duct tubes sit there and bake in the engine bay as the years pass by, they get brittle and begin to crack (thus creating air leaks). I replaced ours with the all-aluminum tube kit from Mina Gallery several years ago. It provides a permanent solution to that infamous problem and I highly recommend it....

 

The intake has been inspected for leaks, havent got a smoke machine to test if there is a leak elsewhere in the system, but that particular pipe does hold pressure when put under a vacuum.

Ordered a set of spark plugs as they are due and a spare coil in case the one for cylinder 3 has gone. hopefully this will be the end of it

 

Thought I'd update, got new parts today. Fitted new spark plugs and a new coil pack on the cylinder flagged up on code reader.
I havent been able to take it for a proper drive yet as I fitted during lunch break, but idled fine and no rumbling or misfires that I can tell!

Will take it out for a proper drive tonight to confirm, but hopefully all good!

 

Hopefully fixed. Takes 2 trips (2 warm ups) at least to flag most codes.

You can't normally detect misfires which the PCM can as it's super-sensitive.