UK Car Repair Questions? Ask a Mechanic for Answers ASAP
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When the engine management system detects a fault within one or more of the components, it will do the following:
- trigger the warning light to alert the driver
- trigger the limp home mode (reduced performance) to prevent any further damage
- register fault codes (relating to the fault itself), in the system memory.
The best way to handle this, would be hooking a scan tool to the vehicle, and retrieve the fault codes. As the fault codes should identify the faulty component(S) or wiring to be further checked or replaced as necessary.
The common fault on your vehicle causing this, would be dirt build up around the throttle body, causing the throttle to be uncalibrated.....thus the idle issues....
However, the spark plugs, coils, oxygen sensors and other components can also cause the same thing.
So you are advised to get the scan, retrieve the fault codes, and take it from there. Instead of checking /replacing parts at random.
I can explain the fault codes, and tell you what and how to check if needed.
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I didn't realise there was such thing as a limp mode, but that does certainly seem to be the case. Could you explain more to me about the limp home mode? How is it controlled/regulated? How does the car know there is a fault? Is there specifically anything that strongly indicates an anti-pollution fault? The error codes that have been registered are "throttle body" (as you have just stated) however, the throttle body was cleaned out, and the problem still exists. It is a little tempremental, it can be fine for a whole day, and give me jip the next. The car has been regularly serviced so spark plugs should be fine, just had new injectors put in as a misfires were occurring, the spray pattern was all to pot so that has been cured. Could you maybe give me a few things i could "try out" to fix? Which sensors could i test/clean? I think the coil pack would give a misfire, its definately firing on all 4, so its not coil pack.
The engine control module triggers on the limp home mode (no longer takes info from the air mass meter and other sensors, but works on a pre programmed map in its memory), when a defect is detected. There are many ways to detect a defect, one of which would be getting a signal out of range ( like a sensor is supposed to give a voltage between 1 and 5 volts, and suddenly it gives 12 volts). When a fault is detected, a fault code relating to the fault is stored in system memory, so you can and should retrieve it, to get an idea on the fault origination and fix accordingly. Most sensors cannot be cleaned as these are electronic components, and the coil pack could still be faulty....giving a few sparks and then giving lower voltage sparks causing problems without misfiring.
Having cleaned the throttle (it could still be faulty), and if you do not want to scan for now, and wish to try a few things (although retrieving the codes is recommended), i would check as following;
- make sure you have tight and clean contacts on battery cables
- make sure the battery ground cable (to chassis) has tight and clean contacts
- make sure the engine ground cable (thick cable from chassis to engine) has clean and tight contacts
- check the wiring connectors in engine bay....make sure you have none loose, disconnected or other.
Other than that, you need to retrieve the codes and take it from there ( this would actually save you time and money by getting to the culprit in a faster way, without checking/replacing parts at random).