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Dreaded "Limp Home" Mode....


MadderThanMax
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on a VW 1.9SDi AYQ Caddy???

When it happens, I have no Throttle at all, instead the engine stays at approximately 1500rpm. I've replaced the potentiometer and thought it had gone only to return. I disconnected the MAF Sensor with no change, and the throttle butterfly moves freely when istructed so there's a signal getting there except not to the pump...any ideas anyone??

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Hi there for a minute I had to do a double take, I was beginning to think "Fart & Space Suit"....

Anyway, Here's whats been done:

First off, its a 2001 Caddy Van. Its a 1.9SDi non turbo just a straight Direct Injection Diesel.

Its looking like an intermittent fault, however The RAC Guy diagnosed it as the "Throttle Potentiometer" and that was from an RAC Laptop! Anyway the van was driving fine all weekend with no tell tale signs. I turned right and..... No Throttle! I had no throttle but the idle would rise to 1500rpm. We reset the ECU (i.e cleared the faults) and after a short time it would return. I replaced the Potentiometer and thought I'd cracked it as it appeared to have cured it, curing the fault codes as I went, But 15mins later the fault returned. I was told to check all the connections and make sure that they are clean (Done!) then clean the throttle body and check that it moves freely (Done), then, check the MAF by disconnecting and notice if there was any difference (Done) etc, still the fault continues. I've checked all the hoses and there's no leaks that I can find. My thoughts are, its to do with heat... reason: When I start the van up I have throttle and the car drives fine, once the car heats up say after 15mins and she's showing on the gauge (temp), its then that I lose throttle and we go into "limp home mode" as I'm reliably told so I'm still guessing... I know that its not the pump as if it was, then it wouldn't start?? So I'm thinking it may be a Temp sensor that I can't find that's giving the wrong signal... I'm no mechanic mind you so I'm open to suggestions... (within reason) that it may be.....

Thanks for trying to help though, much appreciated +++

Edited by MadderThanMax
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Well, here's the update!

As you know I had "Limp Home Mode" and no throttle when it happens. Someone had suggested that it may be the Throttle Body itself sticking, a swift clean and lube and .... It still stuck!!! When you remove it (Four set screws later!) check that the Butterfly is smooth in operation and doesn't snag, hang up or stick at any point along the way until closed. VAG com doesn't pick this up as its an intermittent fault and kept sending me back to the throttle potentiometer. I trawled the internet looking for a sign and on the web there was reference on a Peugeot/Renault website it stated that the throttle bodies were prone to sticking on the HDi's it also said as a cause that the shaft that the butterfly bolts onto wears creating end float and leads to sticking. One second hand Throttle body later as a brand new one is £350! and Hey Presto! No limp home mode and all is well again! ++++++:beer:

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  • 1 month later...

Actually not so....

Its been a while so here's the update:

I thought a new throttle body had cured the problem but not so... a day later and Aye Voila! its back again. I contacted someone I knew in the local "stealers" who advised that the new parts were probably coded to the other vehicle therefore now need to be recoded to my van. ( A bit strange, but never mind...) He went on to advise that "it should" in theory re learn that it has new parts and takeover, mine wasn't! So a booking into the stealers and..... they cleared the faults only for it to be doing the same again a day later... Back into the shop and........ this time it turns out its my ECU that's at fault! £800 notes for a new one!!!!! Now its at this point its worth noting that I've driven around in the van for almost 4 years with a "flashing glow plug light" I put that down to a brake switch fault or glow plug fault, both had been replaced. Apparently the "Flashing Glow Plug Light" also acts as an engine management light so when there's a fault it will display as a flashing glow plug light. One replacement ECU later and I'm back to normal, no flashing glow plug lights! So be warned, don't ignore the flashing light, its there to tell you summat.... like an £800 ECU Fault! :eek:

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