Good day to all during these trying times.Advice needed.
I recently had a check engine light which indicated a Fuel Fail 47. Whereupon I cleaned all the intake system from air filter through throttle body and Idle speed control valve. Checked all earths and cleaned all plugs and sockets. As someone once suggested I then purchased a Stepper Motor for a Renault Megane at £8.99 here in UK (if no good small loss), then went through the set up procedure. However the engine rpm surges at standstill from 1100 to 1500 rpm. Now do not have Fail 47 on VCM but it is replaced with Fail 12 - MAF out of range. Checked all voltages at connector, which are OK. As a last resort I actually clamped the bypass hose line to the IACV, the rpm dropped to 650rpm and remained very stable. Quandry is have I just disguised the problem? Is it the stepper motor operating correctly but swinging due to faulty sensor input(s) or MAF or is it something else?
I can replace the stepper motor with a "Jaguar" unit at about £45.
Until resolved I guess I will use my 1975 XJC!
All advice appreciated.

 

I suggest having a look at your evap canister too mine had lost it's one way valve resulting in an open hose. The canister is located in front of the left front wheel down low. Good luck.

 

Hi John,

My first question is whether the shape of the pintle tip on the Megane stepper motor matched the tip of your original one? There are several different tip designs, and if the tip on your new stepper motor does not match the "beveled cone" shape of your original motor, it may not seal properly in the valve.

My second question is whether you cleaned the carbon out of the valve body before installing the new stepper motor? I use a battery terminal wire brush and throttle body cleaner to clean the carbon out of the port in the valve body.

My third question is whether you gave the ECM sufficient time to adapt to the new stepper motor? If I recall, it took my '93 4.0L several minutes of trial and error hunting before it found the limits of the motor's range and figured out where to set it for proper idle speed. I think I eventually got tired of waiting and stabbed the throttle pedal a couple of times and the idle settled down. Since your idle settles down when you clamp the hose, you have proven that too much air is getting past the IACV.

The MAFS code could simply be a reaction to too much unmetered air in the system due to misbehavior of the IACV.

In case you don't have it, see the link below. The diagnostic procedure for DTCs 46 and 47 begins on pdf page 110.

Jaguar AJ6 Engine Management System OBD1 Diagnostic Guide

Cheers,

Don

 

Thanks Jerry, will check.

 

Sounds like you have a small air (vacuum) leak, plus you have to wait a bit for the idle to be re-learned, go for a drive and see if it evens out afterwards

Larry

 

Thanks Don, will investigate.

John.