Dear all,

A warm hello from the cold Netherlands, where I managed to **** of an entire bus full of people by breaking down in a cramped tunnel near the train station.

Before I get onto the exact complaint and questioning I want to give you a quick history of earlier complaints that might be relevant.

-2019: ever since I bought the car in 2019 it has had a rough idle, where the engine would slightly stumble

-2022: in preparation for a long trip to the UK I replaced a few items. After replacing the fuel filter the RPM would start to fluctuate when idling in either park or neutral, yet NOT in drive or reverse. The RPM goes up a to +- 900 and then go down again and the engine will vibrate a little. This fluctuating feels like a breathing and happens constantly every 2 seconds.

-2023 a month ago: the XJ40 would have a loss of power when under load at or just under 2000 rpm. When accelerating from 50km/h to higher speeds, the car would instantly stop accelerating and you can feel it holding in. After two seconds of the RPMs fluctuating at 2000 rpm the car would start accelerating again. Every now and then the check engine light came one, no codes on the VCM.

-2023 one week ago: after some slight snowfall I decided to take the XJ40 to a local car park and may have slightly abused it turning corners and drifting (drive it like it's stolen sort of thing). Two days after, I took the car for a drive and noticed the complaints from a month ago had gotten worse. The loss of power under load had gotten worse. When asking for torque to accelerate the car would even start to physically rock forwards and rearwards while driving, nudging itself forward instead of smoothly sailing along. After two seconds of nudging and growling and the RPMs being stuck at 2000, this would go away and the car would accelerate again. Idling in drive would also cause the car to vibrate and shake every now and then, as if sometimes a few cylinders would not fire.

Now onto today, I was bringing my girl to the train station in a slight rush. When trying to accelerate from a red light the RPM rised, we started moving and immediately the RPM went back down to 300 revolutions. The car started shaking and vibrating and the RPM would try to go up, but did not succeed. I pushed the accelerator further down to try and power myself out of that situation. That only made it worse and killed the engine off. This embarrassing situation was however quickly resolved by restarting the engine and slowly easing up the throttle till the car started moving properly and then I could drive off without problem. The bus driver behind me was not happy about me.

The drive home was interesting as I found out that driving itself is no problem. Just cruising along at 60km/h the engine runs perfectly. Asking for torque to accelerate is still problematic and driving away from a red light is sometimes problematic. I learned quickly that when driving off from standstill it is key to push the accelerator normally, but when noticing the engine starts sputtering and giving up, then quickly releasing the accelerator. This makes the rpm recover and allows the engine to settle for a second. After this there is no problem driving off. When in park with the bonnet open the engine runs fine. The rpms floating up and down is still present, but the car can easily go to 2000 rpm without any problem. It only seems to be under load that the engine wants to quit.

Quick list of items and things that should be good(?). Engine oil is sufficient (15w40 and 8 degrees Celsius), idle air control valve/stepper motor replaced 2022, fuel filter replaced and injectors cleaned 2022, new spark plugs, wires, rotorarm and distributor cap in 2022. Throttle position sensor touchlessly cleaned in 2022. At the moment no warning lights on dash, VCM is clear.

I'd love to hear what your thoughts are. At first I was afraid it was the gearbox, but I'm convinced it is probably the engine after today. I'd love to know whether you agree. My first thoughts go to a faulty throttle potentiometer, a high viscosity of engine oil or possibly a loss of fuel pressure (either fuel pressure regulator or pump).

Douwe

 

I **think** you have a vacuum leak. My 92 has Never failed me, but it has, at times, been very unco-operative. I recently found a/the problem and I **think** I have it fixed. My issue was a bad EGR valve gasket- something I am still amazed about. I suggest going over All of your vacuum lines however you think best (I like starting fluid or brake cleaner) and anything which operates under engine vacuum to check for a leak. The motor will react in an obvious way if there is a leak. Be careful not to damage electronics with these fluids though.
Regards-