The Renault 25 was a sick car - the idle speed was far too high with no accelerator pedal movement at all the car would happily carry on at 30 mph all day. In addition to this problem when the accelerator pedal was pressed the car wasn't really happy about this, it hesitated and gave massive flat spots unless it was given full throttle when it responded OK. An ideal car then for either a Sunday driver or a speed freak, but not much good otherwise. The problem with the idle speed was found relatively easily - the idle air valve that controls the idle speed was stuck in the wide open position. Quite often this sort of problem responds well to cleaning out the offending valve ultrasonically, so off it came and into the cleaner and leave it for an hour. Unfortunately though this unit must have been taken off before by someone with rather less delicacy than us since it appeared to have been attacked internally by a cold chisel - so much so that it was beyound reclaiming and a new one was needed. This cured the first problem but the hesitation & flat spot fault remained. All signals into the fuel injection ECU (Electronic Control Unit) from the engine sensors checked out OK, the fuel pressure was OK, but the fault remained.

      The root cause of the fault appeared to be a wrong signal out from the ECU to the fuel injectors so it was looking like a faulty ECU  not a cheap job on this car..Good job we recondition ECUs or it would have cost the customer a fortune. Will the day ever come when the car is scrapped for the price of a Black Box ?.Or for cars with air bags "Scrap the car but keep the steering wheel - it's worth a bomb" For more info on ECU testing click on ECU

Mot time for your car now has the added hurdle of emissions to pass. Most people resent the added expense of having to pay for repairs to put right faults in this area, often though it is financially beneficial to have your car running at it’s best efficiency. For instance if as with the Renault 19 that we had in for Mot emissions repairs this week you are using 10 % more petrol than you should, then at 10,000 miles a year you waste about £100 in petrol each year. In the case of the Renault the cure was rather complicated because the car had repairs to it’s emissions system the year before on it’s previous Mot that left the car with emissions that only just scraped through. This year though it looked like the fundamental reason for all of the trouble the year before still hadn’t been cured, since the emissions figure was over 10 times the legal amount.  Checking the car over showed the Ecu (Electronic control unit) to be suspect so we took it off the car and tested it. It failed on it’s ability to control the emissions properly, but a new one was lots of money so we reconditioned his old one. Retesting the emissions showed a great improvement – now only 1.5 Times the legal limit -  still not good enough Resetting the fuel pressure to the lower limit of it’s specification got the emissions down to just over the legal limit, in the end though we found that the car needed a new catalytic converter as well.. It is very important with emissions problems though never to replace the catalyst without checking everything else out first. We never fit a new catalytic converter without checking very thoroughly because replacing the catalyst is expensive, between £250 and £500 in general, and while a new catalyst may cure the emissions fault, if the emissions going into the catalyst are too high then the new catalyst will not last long.) In the case of the Renault though it just had to have one, though I suspect that had the emissions not been so high during the last year or so then the catalyst would still be going strong. For more info on ECU testing click on ECU. 

Emissions failure.  The most common cause of rich running faults is the lamna sensor or the ECU (engine control unit) both of these parts are relatively simple to check, to check the ECU strip back the insulation onthe signal wire from the lamna sensor, this wire is usually black. Then hold the bare wire between you finger and thumb then touch your other hand on to the battery positive if the emissions come down then you have a faulty lamna sensor but if the emissions remain the same then the ECU is most likely at fault. For more information on ECU testing click on ECU