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My 2005 Focus with 85k miles had a problem with the sensor in the throttle body giving bad readings, causing it to drop into slooooooow mode. Ended up taking it to a garage where they got the read out codes, and after talking to me for a little while and I paid for the diagnosis (they said a lot of people would try and leave without paying) the mechanic decided to try and clean it out for me.

He said there was a lot of build up in there which he'd got rid of, and the last few months it's been perfect again, However today the error seemingly reoccurred. I managed to pull over immediately, stopped and restarted the car (and the error was gone -- this is the same as was happening before) -- out of gear I gave it a good revving to hopefully clear some of the gunk out (No idea if this would work but I figured it was worth a try) and after that it drove perfectly again.

As this happened before it was about 3 months from the first occurance, to it completely getting stuck in speed limiting mode, I'm concidering trying to clean the throttle body myself, however I'm no kind of mechanic, just a guy who understands how things go together.

  • Is it worth me even trying this as a beginner, or should I just take it to the garage again?
  • Is it worth seeking out a replacement sensor? From what the mechanic said at the time sometimes changing the sensor can work, but they'd generally just swap the whole throttle body out at first thing however he did admit to not having done it on a focus before, only other cars.
  • Appologies if I've missed anything obvious/important -- first time posting here, and as I noted I'm really not a mechanic, but an engineer with good logic, and a tool kit ;) – djsmiley2k - CoW Aug 17 '17 at 11:48
  • How do you know it's the same thing? Maybe you should read the fault codes first. It might be caused by something totally different. – Mark Aug 17 '17 at 12:01
  • @Mark ok - yes that's a presumption although the behaviour was identical. It'll cost me £30 to get the codes, which is fine however last time as the light didn't stay on, there was nothing on there until the error 'stuck'. If I have the error occur at a time when I can drive to the garage without stopping the ignition then I'll do exactly that. However, I'd still like to know how possible it is for me to clean it myself. – djsmiley2k - CoW Aug 17 '17 at 12:05
  • That said, if someone can point me to a very cheap reader on amazon.co.uk that'd work, I'll also consider picking one up myself. – djsmiley2k - CoW Aug 17 '17 at 12:06
  • I'd go for Forscan as it's commonly used and recommended tool for Ford cars. As for adapter, check forscan.org/faq.html#qobd1 - all adapters based on OBDLink SX (STN1100 chipset) are supported – Mark Aug 17 '17 at 12:09
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Yes, a beginner can do it with basic tools. Loosen the clamp on the intake where it is connected to the throttle body, push the rubber boot aside if possible. have a friend get in the car and actuate the valve while you spray moderate amounts of product into the throttle body, let the product work, and wipe away grime.Good how to on throttle body cleaning. you must use Throttle Body Cleaner and make sure it is labeled as sensor safe. Some people try to use brake cleaner for this but it is super harsh and could damage sensors.

Please note that cleaning the throttle body and replacing the sensor only serves as a temporary fix to your issues. You will continue to get "build up" in your intake system due to oil blowby. Clean it yourself if you are in a pinch, but i suggest you take it back to the mechanic and ask them to take a look at your PCV / emissions system - the #1 culprit for oil blowby residue and is not atypical for a 2005 vehicle with 85k miles.Here is WIKI for PCV. Reduce the source of the buildup and then look into replacing throttle bodies/sensors.

Try not to "throw parts at it", encourage the mechanic to diagnose the cause of the abnormal buildup and then replace parts that were damaged from the symptoms after the root cause has been corrected. Lastly, error codes will only get you so far, particularly when dealing with front end emission systems. The computer wont tell you if you have a stuck PCV valve, but it will tell you when you begins fouling other directly monitored components!

  • Thank you for this information, it's given me something to go on. Also, the mechanic literally did a 10 minute job 'cleaning it' basically to see if it made any difference. Swapping out the PCV valve also looks rather easy as long as I can find it. I'll take a look as soon as I can and hopefully get this thing sorted. – djsmiley2k - CoW Aug 17 '17 at 15:27
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    +1 for not advocating a remove & replace mentality. Some excellent advice there. – Pᴀᴜʟsᴛᴇʀ2 Aug 17 '17 at 16:00
  • As a bit of a follow on from this - how easy is it to check the PCV valve myself? Youtuber's make it look so simple - they are literally pulling the valve out, and inspecting it.... – djsmiley2k - CoW Aug 18 '17 at 9:57
  • As for what actually happened - the wiring harness was corroded >_< – djsmiley2k - CoW Sep 19 '18 at 10:58

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