Hello folks!
I've had this problem where my engine rpm fluctuates from 600 to 800 rpm when idling in park on operating temperature (quite specific right?). It's also been idling on the rough side ever since I bought.
I've recently renewed: spark plugs, spark plugs wires, distributor cap and rotor arm, fuel filter and I have had a shop professionally clean the injectors and refitted them with new O-rings of course, new air filter and cleaned everything in the air intake up to and including the throttle body butterfly valve (didn't succeed in removing the throttle body though..) .
I'm replacing my idle air control valve tomorrow and will also check for vacuum leaks. There's no visible leaks around the injectors/fuel rail and will probably drill a tiny hole into the bottom of the throttle position sensor in order to clean it from the inside out.

Now onto my question: last time I got the mass air flow sensor out I was planning on cleaning it, but was surprised to find it just being a hollow tube, no visible actual sensor. So here's the possibly very dumb question: how can I clean it? Do I dismantle it before getting to the parts I'll need to clean? If so, how can I safely do that?
I didn't mess around with it too much last time, as I was afraid to break anything on my precious (read: costly) maf sensor.
I know how to physically clean it by using MAF cleaner, not touching anything and letting it dry out fully before installing. :-)

Ang tips are well appreciated, even tips regarding the rpm fluctuations. I don't necessarily appreciate my 4.0 revving up on its own with these petrol prices...

Douwe

In case you're on mobile: 1991 XJ40 4.0 sovereign

 

Hi Douwe,
My maf sensors have a screen in them of about 2mm mesh. The sensor itself is in the box area inside a small "orifice" tube- I don't know what else to call it. There is a tiny hole at each end of the unit. In the US I can get a product specifically labeled MAF sensor cleaner. I am not sure if it is anything other than electronics cleaner though. I would also check around for vacuum leaks which may cause your undecided idle. Good luck.

 

I've also had problems with fluctuations of idle. It turned out that the tps were worn out. I changed it and the rpm was correct.

 

Hi Douwe,

When you replace your IACV stepper motor, be sure to clean the carbon out of the valve body itself. The main bore accumulates carbon build-up and the stepper motor pintle can't seat properly, allowing unmetered air into the intake. I seem to recall a couple of smaller passages in the valve body that need to be cleaned as well. Easiest to clean if you just remove the entire valve body/stepper motor assembly, but you'll either need a new gasket or sensor-safe RTV sealant when you reinstall the valve. Also, be sure not to power up the stepper motor while it is not mounted in the valve body or the pintle can wind all the way out of the motor housing.

Cleaning the XJ40 MAF sensor is more challenging than on later vehicles where the sensor can be removed from the intake pipe. I use CRC Mass Air Flow Cleaner with the small red "straw" attached to the nozzle. Feed the straw through the wire mesh and and spray a liberal amount of the cleaner into every opening in the MAFS. I rotate the housing through 360 degrees while spraying into the openings to try to ge as much cleaner as possible into the interior where the hot wire resides. I find that it does no harm to hold the MAFS at an angle that allows you to fill the sensor housing with cleaner and let it soak a couple of minutes, shake it out, then repeat.

I have found that CRC Electronic Contact Cleaner does not seem to remove MAFS deposits as well as the Mass Air Flow Sensor cleaner, so I assume the forumulations are different.

Cheers,

Don