As some of you know, Dad has a grp4 Audi coupe ur-quattro, with an S2 "3b" 20v in it. Still running Motronic albeit with a "chip" burned onto it, Porsche (bigger) AFM, hybrid turbo and some other mild fettling. I keep getting a fault related to the throttle pot, it's a pot as opposed to two limit switches. Anyone know the proper measuring values? I'm using a generic Launch diagnostic machine as I don't have VAGCOM. Basically every time I turn off the kill switches, the engine is a bit lumpy on restart, and hunts like a Mitsi evo rally car when you bring it off idle. There's a very noticeable "whooshing " at the turbo, like a wastegate is dumping etc. I can clear the fault, car runs smooth as silk til the key is turned off. Instantly the hunting is back. Any thoughts, good folk of CGTI?
It hasn't got a stepper motor on the throttle body like a obd2 vr6 has it by any chance? We get a similar issue on the mk3 racecar because it cuts all power to the ECU and therefore the throttle body has to adapt every time you turn it on and if you fire it up or give it any throttle while its trying to do the adaption it throws a wobbly! Just a thought.... Sent from my iPhone using Tapatalk
No, not that, but not a million miles out... Turns out the previous owner removed the ISV, and wound up the throttle stop to compensate, so the idle switch in the pot was never getting pressed. Simple when you know...... Still throwing an N75 ground signal error on occasion, with 2 valves. Wiring tests OK back to the ecu... Might be just one of those things as it's still pulling like a train.
The pot simply returns a 0-5v signal back to the ECU. If you get a multimeter on it with the igniton on you should see a 0-5v sweep as you open and close the throttle. However... its rarely a true 0-5v, zero throttle is likely to give a small voltage i.e 0.5v whereas full throttle may be 4.5v If the throttle body has no idle switch then the ECU will be calibrated to know when the throttle is closed based on the TPS value, i.e the ECU is in idle mode if the TPS voltage is 0.5v or less.. if someone has subsequently wound the throttle stop in then the ECU may now be seeing 1v with the throttle closed and therefore never engage idle mode.. this often throws errors as the ECU realises its never seeing idle..
No it actually has an idle switch, as well as a Pot. All working fine since I tweaked the mounts and brought it back into proper alignment.
Make nice sounds! Lol. He has it for a good while Mickey, uses it in classic/historic events such as Eifel rally or Goodwood FOS and as a course car in club rallies.
