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Peugeot 205 Bosch motronic spi injection bad idle running problems etc etc how to fix or diagnose


Tamworthbay

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Having found a complete lack of info on this I thought it would be useful to put down what I have found out about the system, especially as it’s also found on several Rovers which inhabits these pages. I am no expert but had the help of one, hopefully it will all be obvious and taking a bit of time to understand the system really helps. The crap thread name is so it can be found if anyone searches for it.

 

The motronic system is a single injector system which is a complete evolutionary dead end that wasn’t around long. There are a few components that can give issues, I will try to go through what can happen and how to check each bit.

 

Throttle body - the carb like bit with a butterfly and where the injector sits, also home for the idle control valve, ICV and the throttle position sensor TPS

 

Injector - injects fuel obviously, check by taking off the plastic ducting and looking to see if it makes an even and fine mist of fuel that changes in volume as you actuate the throttle.

 

ICV - can be the cause of erratic idling and often blamed when it’s not at fault. To check watch for it moving in and out when the engine is cold, it can can also be tricked into moving by holding the throttle off its stop. If it’s moving then chances are it’s fine. If not then clean first and replace if it still fails to move.

 

TPS- the problem on mine, sits at the end of the shaft with the butterfly on. There are two wiper tracks, one for small and one for large throttle openings. This really needs a decent meter with graph function to check properly. Without one you need to check that the output voltage is zero at the bottom end, this is critical and often overlooked. If it’s not zero the ecu doesn’t know where the throttle is and tries to compensate with the ICV that then dances around buggering it up more. You may need to take off the ICV to be able to check the bottom end is doing what it should. If you have an erratic idle but the ICV is working, remove the lead to the ICV and if the idle improves then there is a good chance it’s the TPS. Replacement ends are available on eBay for £3 and it’s a two minute job to change but make sure the positioning is maintaining as they are slotted to allow for a range of adjustment. Can be reset using previous multimeter readings for resistance at top end of range.

 

Lambda sensor - will correct other issues to some degree but then gets overwhelmed. If emissions are ridiculous then lambda may have failed - or may just have been overwhelmed. Disconnect and if it runs worse then chances are sensor is ok.

 

Crank position sensor - I never need to mess with this so not sure how to test, sorry.

 

ECU - according my friendly ex-Rover expert who was responsible for making these work on Rovers the ECU is the most reliable part of the system and only worth checking as a last resort. The exception to this is if a coil has recently failed as they can take the ECU with them apparently.

 

Wires and connectors - as with any old car, there is a chance it’s the wiring between the components so check continuity/ resistance and look especially at the connectors on the throttle body and lambda sensor as they have a hard time.

 

Other tricks - letting the car idle for 10 minutes with no input at all allows the ECu to relearn the idle position and settings. On Rovers it can also be done by turning the ignition but not starting the car and cycling the pedal up and down 5 times then starting the car.

 

Air leaks on plastics are not as critical on these as there is no MAF and air flow is purely calculated on TPS settings against a map in the ECU.

 

Hopefully that may be of use to someone. They aren’t that complicated when you get your head around them but a world away from a carb!

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