High fuel consumption and strange idle

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CiderPolo
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Posts: 15
Joined: Fri Jun 07, 2019 12:52 am
Drives: 1999 Polo 6n 1.4 16V 100 AFH & '96 1.4CL
Location: Herefordshire/Powys

High fuel consumption and strange idle

Post by CiderPolo »

Hi All,
I hope all's well during harvest!

I have a 1.4 16v AFH polo '99, and was suffering high fuel consumption and strange hunting idling between 1400-1600rpm if I put the clutch down from higher revs, ie coasting down a steep hill, but if I dipped the clutch having taken it down braking to ~1000 revs it would normally stay there, increasing slightly to around cold idle ~1100rpm. Fuel consumption also suddenly much higher round 20mpg and engine smelt very hot with scorching to touch rocker cover at ends of journeys.

So I read extensively here (many thanks whoever set this place up!!) and replaced the water temperature sender, as well as vacuum hose from MAP sensor to fuel rail that was a bit limp and loose (other vacuum hoses already silicone).

I spotted a small crack in the brake servo vacuum too, so decided to fix that. You can't obtain the correct brake servo vacuum tube from VW anymore so the easiest fix is to chop it just above the damage (normally where it's been stretched over the hosebarb) and use a heat gun to persuade the original thinner diameter back onto the barb. slight wiggles and it all fitted back OK.

After ECU reset just to make sure went for a test drive. This is where I'm confused.

Fuel consumption appears to have been improved - I got about 40mpg vs about 25mpg before. But too early to really tell owing to short distances covered (~55miles).
There is still strange idling.

When completely cold, great pulling, no problems, idle at 1150 on dial, I'm assuming cold idle speed.
Warms up a bit: idling starts high at ~1400rpm, dropping in stages slowly over up to a minute.
Once completely warm idle mostly stable (not always) but will, when dropping to idle from over 2000rpm, will stop and linger, almost 'bounce' around 1400rpm before dropping slower to around 950rpm, which seems to be the lowest idle speed I've seen.

Engine doesn't seem to run as hot as it was doing (though gauge on dash remains resolute at 89-90C no matter what, it seems).
But the fact that the idling still isn't quite right concerns and puzzles me.

Has anyone got any idling advice or experience they can share? It would be much appreciated by a man trying to make cider not fix his car during harvest! Should I be worried, or will it settle itself?

I should add that the throttle body was replaced about 3000 miles ago which solved a variety of previous problems, as was the thermostat and housing which was broken, so I hope it isn't that...
CiderPolo
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alexperkins
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Re: High fuel consumption and strange idle

Post by alexperkins »

Welcome

Have you replaced the sparks, leads and dizzy cap? These can cause strange running at normal operating temperatures. The fact you have replaced the TB already is good though was it adapted properly with VCDS/Vag-Com?

Equally, when was the last time it had a fuel filter change?
CiderPolo
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Posts: 15
Joined: Fri Jun 07, 2019 12:52 am
Drives: 1999 Polo 6n 1.4 16V 100 AFH & '96 1.4CL
Location: Herefordshire/Powys

Re: High fuel consumption and strange idle

Post by CiderPolo »

Hello Alex, and thanks for the reply.
The sparks are new, about 3000 miles old, as are the HT Leads. THe dizzy cap is a replacement from a 1.4CL as the original (and breaker arm) seemed a bit burnt out (ie not new, but workign fine on the other car at time of donation).
I will look at getting a new distributor cap and arm. I have never replaced the fuel filter, though I do have one spare as it happens. Where is it? near the fuel tank?

I have absolutely no idea how to correctly adapt a throttle body with VCDS/VAG-COM (which implies it probably isn't correctly adapted?) I will search here for any guide (unless you can reply with a handy link?)

My ECU reset is simply to disconnect the neg battery terminal overnight and connect in the morning, turn on ignition (not engine) and leave for 5 mins, turn off and on again, "Job Done" so to speak. I expect that isn't the whole story....

Many thanks,
CiderPolo
CiderPolo
New
Posts: 15
Joined: Fri Jun 07, 2019 12:52 am
Drives: 1999 Polo 6n 1.4 16V 100 AFH & '96 1.4CL
Location: Herefordshire/Powys

Re: High fuel consumption and strange idle

Post by CiderPolo »

Morning,

So the VAG COM arrived and I have the follwoing codes:
ENGINE
00516 Throttle position sensor closed switch F60
00518 Throttle position sensor signal oout of range G69 Also check for for loose ECM power relay
00530 Throttle position sensor G88
01265 EGR Vacuum Regulation Solenoid Valve N18

I think this may point to an electrical fault or intermittent connection perhaps? Or is a new TB what's required. The one I bought came from Germany but wasn't OEM.
For the EGR I have no idea how this should/can be fixed. It's the thing corrosion welded onto the exhaust manifold, right, witha vac tube going to it?

SRS
00532 Supply VOltage B+
PLease can someone explain this to me!

ABS system
00283 (twice) ABS wheel Speed Signal #1 (Left Front) Range/Performance G47
01276 ABS hydraulic pump - V64
IS this a sensor on the wheel and an issue with the pump? SOunds like an expensive job!

Any wisdom or previous experience of issues around these codes would be much appreciated!

Tom
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