idle problem....

[snarloas]

hi guys, newbie here.

i just got my girlfriend a 2002 1.2 polo. its was running fine until i noticed recently that the idle is dropping slightly to about 700rpm. its causing unwanted vibration through the car. when i acclerate it goes perfectly smooth. i only get this problem when the car has heated up to normal running temperature. i have cleaned the throttle body which was full of black goo it ran slightly better for a short while. can you gus give me a few tips on what i can do myself before i take it too the garage

[alexperkins]

Replace the temperature sensor mate. The car is infact a MkVI - Mk6 which is a 9n polo, not a MKIV or MK4, which is a 6n

[snarloas]

is thet the sensor at the front of the engine? the lamba sensor?

[snarloas]

ignore my last post i seen picutres of the temp sensor on this forum

[snarloas]

may i ask why you think its the temp sensor and not the throttly body?

[alexperkins]

Because its happening when the car is hitting idle temperature, which is highly unlikely to be be a TB related problem

[snarloas]

thank you very much, i will get straight onto replacingthe sensor

[alexperkins]

sounds like a plan

[NOZ]

AND its one of the most common culprits for idling issues lol.

[snarloas]

changed the sensor, still vibrating at idle (running temp) not as bad though. gonna disconnect the battery to reset the ecu. will get back 2moro

[snarloas]

well after a day of driving its almost cured it, if i get the vibration its only for a short moment then it straightens itself out. i.e put brake on when going to idle it gives a judder then goes away. still there slightly but alot more pleasant to drive

[snarloas]

ok after a bit of futher testing i found its sort of fixed the problem at idle. i find that when i use any electrics at idle i.e the windows and especially the fan the idle drops slightly and the car vibrates very quickly. do you think it might need a better battery or altanator to cope with the electrical draw?

[alexperkins]

Sounds like the voltage regulator in the alternator may have gone. Get the battery and alternator tested, as either or both may need replacing.

[snarloas]

ok checked the battery read 12.5 with engine off, engine it was 14.5 it stayed steady even with revving the engine to 1500rpm. so i guess that pretty much eules out that bit.i have been looking at that vag software can i manually up the rpm slightly with that software?

[alexperkins]

Battery sounds ok. I think its most likely your alternator. Mine had exactly this problem, and I had to replace the alternator to fix it.