Fuel economy

Changing the Lambda sensor

If you’re experiencing poor fuel economy in your 106 GTi, one of the primary culprits is the Lambda (or Oxygen) sensor malfunctioning. The Lambda sensor reads how much oxygen remains in the exhaust after the combustion process. This tells the ECU whether to inject more or less fuel into the cylinders. If the sensor is not working correctly, the ECU often injects too much fuel, harming the fuel economy and not doing much good to the Catalytic Convertor. To find out if your 106 could be suffering poor economy, use the Around 35mpg is usually the average returned by a GTi.

Replacing the Lambda is a bit of an awkward job as it is located behind the cast iron exhaust manifold which does not make it easy to get a spanner on the sensor. The oil filter also hinders the process. To solve this problem I bought a lambda sensor spanner, designed to hinge and make getting a grip on the sensor easier.

First remove the plug on top of the gearbox. To get to the loom plug, you have to remove the Airbox. This comes out easily enough, just disconnect the hose from the throttle body and cold air feed and lift the box out. This should expose the lambda sensor plug on top of the gearbox with a red tab. Pull the red tab out and remove the plug from the loom.. Now get the car up in the air and secured on Axle stands. Get underneath the front end, and you will see above the oil filter and behind the manifold the lambda is visible. Try placing the spanner on the plug. Hopefully after some trying (and swearing) you will get a grip on the lambda and you can undo it with some force. Withdraw the sensor and pull through the wire. You may find you have to remove the oil filter to gain enough access. In this instance you may as well carry out an oil change (see ) as you will lose a lot of oil from the filter anyway.

I removed the filter, and even then there wasn’t enough room to get a spanner on the lambda. So I ended up unbolting the lower part of the manifold and dropping it down. This gave enough room to manouver the spanner and remove the sensor.
The replacement sensor I bought was part number 238 038 717 available from any good Bosch dealer and some stockists on ebay. The Peugeot part number for reference is 1429 N2

In true Haynes style, fitting the new part is the reverse of removal but take car not to touch the end of the sensor as it is very delicate.

Fitting a new throttle cable

Throttle CableEver since buying the car the throttle has been pretty stiff in its operation. I noted when doing a service that the path of the accelerator cable from footwell to throttle body looks very easy to change, being high up on the offside of the engine bay. So with a couple of hours set aside, I quickly set about removing the old cable and replacing it with a brand new one from Peugeot. Since the car is 10 years old, it makes sense to replace cheap parts like this now, rather than risking them snapping in the future and leaving me stranded at the side of the road, awaiting recovery, hence the clutch cable is also on the list for a future job.

I spent £20 at 106 parts.com and a cable arrived after a couple of days. The kit comes complete with the whole assembly including outer cables etc. I decided I was only going to replace the inner cable as that would make the most difference and is a lot easier than replacing the whole thing.


Swapping the inner cable over is a straight forward job. First locate the throttle body at the back of the engine bay where the air filter hosing goes in toward the inlet manifold. Turn the throttle butterfly and remove the cable. note how frayed and old my old cable was. Now open the drivers door and press down the accelerator. You should be able to push the plastic clip out which holds the pedal to the throttle cable.  This part is optional: Tie some string to the end of the cable and pull the cable through the footwell to remove it. When I did this i found the string came off anyway.

Old frayed cableNew cable pulled through

Take the new cable and lying the old and new side by side check it is correct. Tie the string to the new cable and pull it through the firewall into the car. Alternatively (as I did) just feed the new cable back through the outer cable and it will appear in the engine bay.

Its a bit fiddly but attach the new clip to the pedal and from the engine bay route the cable and offer it up to the butterfly so you know where to cut the cable short. Once cut, you can fit the clamp onto the end of the cable and refit to the butterfly. You may need to adjust the clip on the throttle body end of the cable to take up/give some slack as necessary.

Pedal clip

Now take it for a drive!

What a difference! The accelerator is now feather light and smooth. I’m actually convinced it will help the fuel economy as it now feels adjustable by a minute degree rather than the feeling you had to stomp on the thottle before.

Changing the Coolant Temperature Sensor

airboxIn an effort to improve the MPG from the 106 I decided to replace the Coolant Temperature Sensor on the thermostat housing. This sensor is used to ‘tell’ the ECU what temperature the coolant is at. If the sensor is sending erroneous readings to the ECU, the ECU may inject more fuel as it would during a cold start.

You’ll need:
1) The Part number for my 98 model was 1920.3F from Peugeot.
2) Flat headed screwdriver
3) Cable tie cutters
4) Spare Cable tie
5) 19mm spanner

To access the sensor you need to remove the airbox. This is a simple job.

Undo the jubilee clip on the air pipe at the top rear of the engine bay. Then disconnect the breather pipe going to the airbox. Finally remove the cold air feed at the front of the bay connecting to the airbox – you may need to cut a cable tie to remove this. Wiggle and pull the airbox upward and out.

Now you should be able to see the green sensor on the right hand end of the cylinder head.

Now ensure the coolant is cold, so you don’t burn yourself, removing the sensor.

Coolant Temperature SensorUnclip the loom by pressing in the spring clip and withdrawing it from the sensor. Unscrew the sensor using a 19mm spanner and replace with the new sensor.

Refitting is the reverse of removal, replacing the cold air pipe cable tie if necessary.

I will be keeping an eye on the MPG over the next couple of tanks to check if I see any improvement.

Don’t forget the to you’re having issues with fuel economy.

Rear Brake renewal

For weeks I’ve noticed the rear brakes sticking on, particularly at the beginning of a journey. I finally got round to ordering some brake discs from BuyPartsBy for the princely sum of £21 delivered. Since I already had  a spare set of rear brake pads from the 306 which shares the same rear caliper, it was time to get started and sort out the rear brakes.

With the sun shining it wasn’t too much of a chore. I timed it right as the pads on the nearside were almost down to their backing plate and were clearly not contacting the disc 100% of the way across.

I removed the pad carrier, cleaned it out, replaced the pads and greased the sliders. I then wound back the caliper pistons which were extremely stiff, but loosed up eventually with a little persuasion and copper grease. I noticed the dust boots need renewing at some point in the future but I’ll leave that for now. A bit of threadlock on the bolts and the car was dropped back down on it’s wheels.

I took the car for a drive and the difference was notable, no drag from the brakes, and the car felt livelier and more responsive – clearly it was being held back quite significantly before. Hopefully eliminating the binding brakes may well help to improve the fuel economy as well (see mpg post )

106 GTi MPG

I’ve suspected for a while I’m not getting the MPG I should be getting in the 106. I’m not looking for diesel economy, but I think 35mpg should be achievable on a run. As any owner will tell you the 106 fuel gauge is shockingly inaccurate, so I’ve written a little to find out my actual mpg.

Working it out I seem to be getting approximately 270 miles to 45 litres which is ~27mpg. I have an idea what might be causing this figure to be a bit lower than it should, namely binding rear brakes which could easily be causing drag and causing poor fuel consumption figures. More in another post…

Click to try the MPG tool yourself.