Hesitation on part throttle.

[Heat Seeking Missile]

I've noticed on my S2 that when gently accelerating through the gears, I get a very slight hesitation when I'm on part throttle, usually between about 2200/3100rpm. I noticed the other morning on the way home from work, that when doing 70-75mph, I could feel the engine pulling, and then easing back and then pulling again, which is in the rev range stated above and still part throttle.

A run at WOT shows no problem what so ever, it boosts to 0.8/1.2 bar perfectly, this problem only seems to rear its head when the boost gauge shows vacuum or zero.

I've got a new WGFV and a new RS2 MAF, so they're probably pretty much ruled out, everything else is standard except for a Pipercross panel filter and a Milltek exhaust.

I found this thread using the search function, does it seem like the same thing?

http://www.s2forum.com/forum/showthread.php?t=27699&highlight=hesitation

Thanks,

Mark

[A80Avant]

check your lambda.Mine did that at one point as well,and since on part throttle,lambda is operational it could be dodgy and causing this issue.On WOT lambda is bypassed and so the car goes fine.
In greece sometimes bad fuel generates this issue and after a while it goes away...

[Heat Seeking Missile]

Its just gone through an MoT with no emissions issues, will a faulty lambda still allow this? It runs on Shell V-Power, rather than any old cack.

Mark

[A80Avant]

well good emittions is a good point,but if you have a spare or a test lamda to see,it could still be knackered

[Flat on my back]

.

I'd be tempted to change knock sensors first...if you have spares.

[Heat Seeking Missile]

How much are knock sensors, and are they difficult to replace? Would that throw up a fault on VAGCOM at all?

Tried again this morning to get some more information that may help and found that, once the turbo is on boost, the problem goes away, even down to as little as 0.15bar of boost. I'm pretty sure the problem only occurs when actually on vacuum.

Mark

[Flat on my back]

.

They are expensive from the stealers... see if peeps on here can lend you some...then try vagparts.

Auckward/fiddly to change but not difficult.

If they've gone kaputt they should show a code, but if intermittent may not.

Make sure the throttle body and isv are clean, usual, plugs are all tight, check them when they go back in.

If you have a spare plug/lead (3b or aby) try a swap one at a time, as well as a boost leak check.

Allway at the same revs no matter the gear points to a knock problem, imo.

[Heat Seeking Missile]

Where abouts is the knock sensor? What does it look like?

Mark

[Heat Seeking Missile]

Right, found the knock sensors. One looks alright to get to, the other one, not so easy. Is there anyone local who can give my car a quick VAGCOM before I start pulling all sorts off it? Crate of beer/bottle of wine in it for whoever.

Mark

[spink]

im pretty sure a faulty knock sensor doesnt show up a code,in fact i read somewhere that there is no way of testing them just a case of replacing and hoping for the best.

[S-Express]

Right, found the knock sensors. One looks alright to get to, the other one, not so easy. Is there anyone local who can give my car a quick VAGCOM before I start pulling all sorts off it? Crate of beer/bottle of wine in it for whoever.

Mark

Mark, I'll be in tomorrow morning if you need to vagcom......

[Greg_S]

I might still have a couple spare in the shed that I replaced a few years ago trying to trace a fault but the knock sensors weren't causing it

[Heat Seeking Missile]

The rubber pipe from the the intercooler pipe to the throttle body isn't looking too clever, something I probably should have replaced a while ago, but I'll see if vagcom throws anything up first.

Alex, I'll be out mountain biking tomorrow morning but my other half is going with me, so should be back for late morning if thats ok? Do you still have my mobile number?

Greg, I might take your offer up of those sensors, I'll see how it goes tomorrow. How come they dont throw up a diagnostic code? I'd have thought it was something quite important to the engine, especially if it isn't working properly.

Mark

[S-Express]

Hi Mark - yes still have your mob.
give me a bell if your about.
I'm around most of the weekend at some point or another!

[Heat Seeking Missile]

Cheers mate, much appreciated. Will give you notice as to when I can nip over rather than just turning up. I'll drop you a text tomorrow when I'm back from Llandegla forest, providing I haven't fallen off my bike (again) and broken something. It'll probably be about half 11 12-ish at a guess.

Mark