Thread: MAF & fast idle

The PCV lines are a good start. These hoses crack.
The other thing with the stepper motor, at least on the Classic anyway, is there is a vacuum hose from the fuel regulator to the very back of the manifold. If this has cracked or fallen off, it allows enough air to lift the idle significantly.

Either that or someone has been playing around with the air idle bleed screw on the manifold. (Another Classic thing... Need to get a P38 me thinks....)

From what you are saying, I'm going to assume you have a hot film type MAF sensor. That screen on the front of the unit plays an important part of fuel control. It is there to smoothen out the air flow. Take out turbulance. The same reason why the actual measuring part of the sensor is jammed inconvieniently in a tube. That tube is there to reduce the impact of engine pulsations (valve action ect).
On a scope this is all (including each engine pulsation) very visable. It is a very sensitive componant. When cleaning I would be (assuming it is hot film) very cautious. It is for this same reason they are liable to failure. As for confirming a faulty MAF sensor, I wouldn't rely on a sacanner. An exchange with a known good one will give you direction. A scope will point out bad ones before a scanner. Hope this helps.

Originally Posted by PhilipA

The wire mesh is there to ensure that air flow into the MAF is uniform, if there is not about 30CM of straight tube in front.
In the 14CUX, you can remove the mesh by levering on a spring retainer.
In any case, where you want the cleaner is in the sampling tube of the MAF on older ones (hot wire type) or on the film surfaces of later type ones (hot film type).
There are two small wires in the sampling tube which you should be able to see when they are clean. The hot film type has a double sided "blade" sitting in a holder in the middle of the MAF tube.
Spraying the mesh in either case does nothing but make it look nice.
Regards Philip A

PhillipA or anyone out there ......if we are talking about how to clean these MAF sucker's ....then don't we need to know HOW THEY WORK or the sensing or sampling difference in MAF's between Lucas 14CUX, GEMS and Bosch Motronic???

For instance everyone rolls off the tongue Hotwire 14CUX 5AM and or Bosch hot film MAF specs......they can or can't work with oiled/K&N air filters etc etc with confidence?? What about GEMS?????

It seems to me a GEMS 20AM MAF no one is quite sure about how they work???? For instance (and we are speaking MAF only).....is a GEMS 20AM a simple hotwire 5AM upgrade that everyone has forgotten about OR something more significant???

Is the bucketing Bosch hot film MAF's (10 years old) justified???? If so does this mean a GEMS MAF albeit 15 year old is far better????

Love to be illuminated

PhillipA or anyone out there ......if we are talking about how to clean these MAF sucker's ....then don't we need to know HOW THEY WORK or the sensing or sampling difference in MAF's between Lucas 14CUX, GEMS and Bosch Motronic??

Well all MAF work by measuring the MASS of air entering the engine. A hot wire samples the air by taking a fixed proportion of it through a tube.

The measurement is done by measuring the resistance difference between a wire heated to a known temperature and another wire. The cooling effect of the incoming air cools the hot wire . Hot film works much the same but on all the air.

This automatically makes compensation for air temperature unlike the flapper which measures air by the mechanical lifting of a flap which only measures the volume of air.

The 14CUX is particularly unsuitable for use with a K&N because it is one of the only (or THE ONLY) ECU that does not pulse a burst of high heat through the hot wire as you turn off the ignition. This is designed to burn off any oil. The 5AM Hitachi MAF is used in many GM cars and they do not have the problem to such a degree as Range Rovers, but they still do have it.
I do not know about the GEMS ECU, but I would be surprised if it did not institute a burn off phase, so using a K&N would not be such a severe problem. Its not the MAF so much as the design of the ECU.

So, when oil or other stuff gets on the hot wire it acts as insulation which alters the temperature effect of the incoming air.
Enough???
Regards Philip A

Thanks PhillipA.

My 5AM is on the way out so intend wiring in a 20AM MAF for larger airflow and hopefully it has the burnoff feature you speak of. I need to source the right potentiometer to adjust CO signal as this not on the 20AM.

Same conversion could be done with the Bosch but I get the impression they are troublesome when you don't here of any problems with earlier MAF's

It's not the MAF which determines the "burn off" it is the ECU, so unless you change your ECU you will not achieve that.
But the conversion to the later MAF seems straightforward ( on the RPI site), but really only useful if you have a big capacity motor and want max high rev power.
Regards Philip A

Thanks PhillipA. I am tossing up doing a gradual 14CUX to GEMs swap with a larger engine (stroking an GEMS donor) or sticking with the 14CUX (and stroke anything).

The simplicity of the dizzy 14CUX Versus of the GEMS kiss the dyno goodbye after initial setup is an interesting pros and cons exercise.

Well my problem is sorted. After scouting round on the forums, I found a guy that other members could not reccomend highly enough. Ricks 4x4 at Nerang. I rang Rick and he suggested that it sounded like the base idle had adjusted itself. When I got there, he hooked up the computer, found that his suspisions were right, and as soon as he adjusted it back to standard, it now runs like a dream. And I got change out of 50 bucks too!!!
If anybody else gets a problem that they cannot fix, and they are around the Gold Coast, call Rick. The man is a magician and does not charge huge fees.


The only question that remains is why did it fix itself last time it did this??? Computers in cars, what a good idea that was!