Hello,

I have an issue with the idle, i've got a 1.6 single point injection swap in my polo and the idle drops so low the whole dash rattles, but it isnt steady, it fluctuates, like it is trying to keep it up.

When I hold my foot on the gas pedal lightly, there are no fluctuations in the engine rpm, drives and runs fine for what it is.

Was thinking the 1.05-1.3liter SPI are pretty much the same engines, and maybe someone has encountered this issue.

Could it be a vacuum leak?

1.6 SPI? Is that a typo or a real thing? Whats the engine code (AAV, AAU etc)?

 

Things I can think of

• Seal around throttle body isn't letting any air in
• Vacuum hoses leading to TB aren't cracked or missing
• TB isn't filthy - give it a clean with some carb and intake cleaner - don't touch the throttle butterfly!
• Fuel filter isn't blocked
• Air filter isn't blocked up
• Check the condition of your plugs

The SPI throttle body is electronically controlled and doesn't have any idle adjustment. If the idle is off its likely unmetered air getting in. Spray some WD40 around the base of the TB when its running and see if the engine note or revs change.

I will check for those things possibly during this weekend.

My vac pipes are disconnected and plugged off except the brake booster, of course.

Why shouldn't i touch the butterfly? I think I already have done that

And yes, it's a real thing, ABU from MK3 Golf.

Edited 10 December, 20196 yr by GatisGirdenis

Ahh fair enough! Not got any experience with an ABU but it's throttle body probably isn't vastly different, or at least the principles are the same.

 

The advise not to touch it comes from its sensitivity - its possible to move it out of alignment with the throttle position sensor. The idle position is sensed by the idle position sensor which is a little switch on the side (on mine at least).

 

How, or if, this can be adjusted on an ABU TB is another matter though! On the AAV its not supposed to be, although some forum members appear to have had luck in the past

Edited 11 December, 20196 yr by zob
clarity

21 hours ago, zob said:

• TB isn't filthy - give it a clean with some carb and intake cleaner - don't touch the throttle butterfly!

Any tips for cleaning the rear of the butterfly ?

Just now, vwfan3 said:

Any tips for cleaning the rear of the butterfly ?

 

I cleaned mine by opening the throttle (pulling the accelerator cable) and spraying over both sides. Although to be fair it was pretty clean to begin with. This being a mechanical throttle though - a fly-by-wire I suppose you could rev the engine to get to the underside.

 

Other option would be to remove the TB and clean it from the other side that way. The advice for 'no touching!' is to prevent people jamming a screwdriver down there or something - washing it over with carb cleaner is gentle enough i should think!

I tried to blow some wd40 around today, nothing happened anywhere, few things I noticed.

There is a big groove rubbed out of the brake booster vacuum line right at the intake manifold bung, might have to come up with a fix before it's rubbed through although I dont see where it would rub against. Held my finger on the groove, didnt feel any vacuum.

The rubber base of the injection unit is heavily cracked, but as I was spraying, nothing really changed in terms of revs. Is the base hard to change? Do the screws rust in badly?

And about the idle sensor, I didnt pay attention too much, but noticed that there are threads on it, so it might be adjustable?

36 minutes ago, GatisGirdenis said:

I tried to blow some wd40 around today, nothing happened anywhere, few things I noticed.

There is a big groove rubbed out of the brake booster vacuum line right at the intake manifold bung, might have to come up with a fix before it's rubbed through although I dont see where it would rub against. Held my finger on the groove, didnt feel any vacuum.

The rubber base of the injection unit is heavily cracked, but as I was spraying, nothing really changed in terms of revs. Is the base hard to change? Do the screws rust in badly?

And about the idle sensor, I didnt pay attention too much, but noticed that there are threads on it, so it might be adjustable?

 

No idea about adjustment on yours - as I said before they're technically not supposed to be on the mk2f. Its more likely that one of the fundamentals (air, fuel, spark) is off but i may be wrong. Is the TB all clean inside its throat?

 

The rubber base is replaceable - part 13 on this picture (I just picked a Mk3 golf year off the top of my head - have a hunt on 7zap yourself to confirm!)

https://volkswagen.7zap.com/en/rdw/golf/go/1993-121/1/129-129050/

Worth replacing if its cracked - they're not expensive. The flange bolts down through the inlet manifold with some nuts on the other side so a bit of a pig to get to while on the car, probably doable from below. Doubt the nuts would be rusted, haven't seen any rusted nuts on that part of my engine yet - all too oily!

 

I'd replace that brake booster line if it looks worn at all - last thing you'd want is for the brakes to revert to their un-assisted state when you need them.

 

You mentioned a bunch of vacuum lines are bunged - which ones and are the bungs holding?

 

Also - is there any difference in this idle problem when the engine is hot compared to cold?

 

Is the timing correct?