UK-POLOS.NET - THE VW Polo Forum

Hi all, I am a newbie here on the forum and my wife's car is not behaving at all well. When we start it and its cold there is no problem but after a few short minutes when you pull up or drive very slowly the car either stalls or ticks over very erratically. I did a basic service,oil,filter, air filter, fuel filter and plugs. This made no difference so i cleaned the throttle valve put it all back together and went for a drive. It all seemed fine so I left it and when the wife drove it today it was as bad as ever! Some more head scratching and poking and prodding revealed that if i remove the oil filler cap when the engine is running it can also stall. There don't appear to be any vacuum pipe leaks but this feels like a breathing problem. What are your thoughts?

Maybe consider replacing the engine coolant temperature sensor as if that is faulty it will affect the fuel mixture (injection spray period).

Since I last posted on the forum I have continued with the run of bad luck with the Wife's Polo. As suggested by RUM4MO I changed the coolant temperature sensor. This seemed to help briefly but the bad idle when hot continued. I called in the Green Flag people and by luck the lad that turned up was VAG trained and had the VAG hand held code reader. He asked all the usual questions and then decided that the throttle control valve was at fault. After an exhaustive search of many local salvage yards i was able to get another throttle body from a car identical in age and spec (crashed) and fitted it. It runs and accelerates as i would expect but when the engine is up to temperature the idle is all erratic again! It just feels as if it is constantly hunting after the O2 sensors have kicked in. Any thoughts as i may have to resort to the Wife's threats of buying a Micra!

I could be wrong, but I'm not convinced that the O2 sensors do much at idle, okay they are ignored when the engine is cold, but I thought their data was only used when "on the move"?

Next plan, all vacuum tubing especially at points where it is connected to T-pieces, and that includes the brake servo pipe, maybe try this, in case you have a leaking brake servo, try finding what is involved with removing the brake servo pipe and plug the end of it some time while the car is stationary and hot and exhibiting this rough idle, restart the car and see if idle is now okay??

From memory, the manifold end of that pipe is not the end to remove as it looks like it would only remove once then need replaced.

Try the thing at the vac control/sensor pipes for the auto trans (I don't know anything about that side of things but I'd reckon the controller will also use engine vac).

Have you used Google to search for "uneven hot idle for VW 1.4 16v engine" - I'm sure that a few people have asked that question across the many Skoda/VW/SEAT/Audi forums.

They dont do much at idle - thats right

Id be looking at a vac leak or something to that effect. It could even be loss of compression or a faulty coilpack.

I have tried a complete set of coil packs a while ago (6 weeks), alas no joy. Does anyone have a set of diagrams showing the run of all of the vacuum system? My car does not have the EGR valve and never has.....

I don't know if you sorted this but I had a similar problem and eventually traced it to the pre cat O2 sensor