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idles rough and dies at idle when hot

4589 Views 6 Replies 4 Participants Last post by  billymade
when my daughter takes it on a drive like over 50 miles, and running the air conditioner, then at a stop light or maybe a drive through she notices rpm gauge fluctuating and sometimes car will die, then start back up. it will also flash the epc on the dash and the check engine light, and also the little triangle symbol what ever that means, The check engine light has been on lately due to code p0420, and now it showing codes p0172, p0171.p0507.p0221 The car runs fine when it cool but lately has been developing these problems, The last time I had a problem similar to this was when I found a wire connection off of the knock senor. but I don't remember what code it was. Any help would be appreciated thanks
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can you give us all the specs and or history on the car so we can try and helpa ya out better. year? mileage? 1.8t I guess? when was the last time u did a full tuneup? when was the last time you checked all the vacuum hoses for leaks? when was the last time you cleaned the throttle body valve? check the grounding wires for rust/corrosion I believe there are three, one under the battery tray, one behind the driver headlight and one mounted to the engine chassis which is a bugger to reach. There is a recall on the coil packs, the valve cover gasket leaks causing problems on these.
OK it is a 2001 beetle with 1.8t. and auto trans. its got 145000, miles. I bought it at about 100k. since I have replaced turbo and charge cooler. all coil packs. spark plugs, timing belt and water pump. oil and temp senders, and basic maintenance like oil change every 5-7000 miles,tie rod ends and control arm bushings, and even an oil pan and a two hundred dollar rim because my daughter cant avoid rocks fast enough. yeah Ive got two much money in this little buggy to give up on her now.( it hasn't been the economical gas saver I hoped for for her) I have not cleaned the maf senor yet but heard that could do wonders, I also haven't checked any of the ground yet, that's a new one to me. Like I said in the first post it usually acts up after a long drive and then coming to an idle quickly. I was hopping some of the codes I pulled off my actron would help. Oh yeah I also taped up some hoses I new were leaking like the one on the secondary air pump
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When someone came in describing this scenario , the first thing I would do is to clean the IAC valve. When it goes bad it does the dying when coming to a spot thing .
You may want to look at the EGR and the PCV valve just for SHIGGLES !!
But that P0420 is a Cat Code so you my friend might be dealing with a partially clogged CAT "if not Fully clogged" that symptom is usually a loss of power like you're chocking the car, you press the gas and if feels like it doesn't have the power it used to...also it will DIE on you!
Then there's the P0221...I just fixed this on a lady's Sienna. The throttle pedal position code came from a blown fuse which in turn would not read the position of the pedal when you pressed it. The Beetle is a drive by wire system so...it could be that or the the TPS or the TPS wiring.
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Ok, what is the IAC valve, the car still seems to have good pep. when you put your foot in it.
The IAC is the Idle Air Control is usually on the throttle body
VW probably calls it something else JUST BECAUSE....then again they could just not have one JUST BECAUSE.
16804/P0420/001056 - Ross-Tech Wiki
16556/P0172/000370 - Ross-Tech Wiki
16555/P0171/000369 - Ross-Tech Wiki
16891/P0507/001287 - Ross-Tech Wiki
16605/P0221/000545 - Ross-Tech Wiki

Quite a few of the trouble codes; are related to the throttle body, I would clean and adapt/align it. You might also; test it, using the troubleshooting steps in the vw service manual. What year and model of New Beetle are you working on? Here are some service manuals online; you can look up the testing procedures for the throttle body:

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