Technical 100HP jerky throttle

[Wazzzer]

Having a bit of an issue with the 100HP at the moment where the throttle is a little jerky. It's almost like it's in the wrong gear sometimes with the throttle trying to kangaroo. I did notice today while sat in traffic that the throttle at idle was hunting a little before returning to normal.

Anyone got any ideas? No fault codes popping up, new MAP sensor fitted last week.

It's really taking the enjoyment out of driving at the mo

 

[koalar]

Having a bit of an issue with the 100HP at the moment where the throttle is a little jerky. It's almost like it's in the wrong gear sometimes with the throttle trying to kangaroo. I did notice today while sat in traffic that the throttle at idle was hunting a little before returning to normal.

Anyone got any ideas? No fault codes popping up, new MAP sensor fitted last week.

It's really taking the enjoyment out of driving at the mo

two things I have seen for this is a low rev misfire or a noisy potentiometer on the throttle pedal.
possible many other causes

just done a throttle pedal on my 2010 1.2L for kangerooing

reseated the cable seem to have fixed it. Looked fine on a data scanner except it would run a little rich on idle

looking at the long term fuel trims would be my first move, Possibly followed by inspecting the spark plugs

 

[A3jeroen]

How clean is your throttlebody?
How are all hoses? Any chance of an intermittent vacuumleak?
Coli on it's way out is another possibility.

gr J

 

[Wazzzer]

Brilliant thanks for the pointers, I'll have a look over the next few days and do some logs.

Coils are only about a year old so I'll look at them last (I know being new doesn't rule them out)

Plugs are on my list to change on this year's service.

Throttle body - I have no idea how clean it is so I'll pull it off soon and give it a good clean. I'm assuming I can't open the flap full due to the motor?

Vacuum hoses - this was my first thought but they look good, I've sprayed carb cleaner around the general area and there's no rise in the revs

 

[DaveMcT]

Do you have an infra red thermometer? (£15 on eBay)
Start the engine from cold and check temperatures if exhaust stubs close to the cylinder head. They should all be heating at he same rate. Note any that are heating slowly. Swap that spark coil with any that are warming normally and retest. If the slow warming cylinder has "moved" you have a faulty ignition coil(s). Buy a full set, because the others will soon be along to spoil another day.

 

[Wazzzer]

Done a bit of driving over the weekend with the sport mode on and off, jerkiness persists.

Also tried it with my Novitec GP1 box in various states and it's still there.

I have hooked up my OBD reader and the throttle pedal goes up to 77 degrees or percentage, is this right?

Also the pedal only seems to start registering at about half - again is this the way the pedal should be behaving?

 

[koalar]

Throttle pedal angle / percentage depends on the software used to measure it

I have multiECUscan, Delphi, WOW and the don’t read the same values.

However if you plot the data it’s a nice slope

From memory there’s no dead zone at the bottom. If there is it’s very small.

 

[Popitinpete]

Having a bit of an issue with the 100HP at the moment where the throttle is a little jerky. It's almost like it's in the wrong gear sometimes with the throttle trying to kangaroo. I did notice today while sat in traffic that the throttle at idle was hunting a little before returning to normal.

Anyone got any ideas? No fault codes popping up, new MAP sensor fitted last week.

It's really taking the enjoyment out of driving at the mo

Got all the classic signs of an inlet manifold/vacuum air leak. Worth a quick look to eliminate.

Check everything from the air filter to the cylinder head, breather hoses for perishing, listen for air rush noises. Spraying a can of carb cleaner around all joints from top to bottom whilst on tickover can sometimes change the engine note and pin point the problem.

Has any work been done to it recently?

 

[DaveMcT]

The most important areas to check for air leaks are between throttle valve and cylinder head. Also check the exhaust manifold is not cracked as that will pull in air and upset the O2 sensor values.

 

[Wazzzer]

I've got half a can of carb cleaner so I'll give that a spray around the inlet side

No work done recently apart from a cam belt change. Are there many pipes to look at for vacuum leaks? Agree it does feel like there may be a leak somewhere. Just wish it wasn't so cold and wet at the mo otherwise I'd be out there now

Thanks for the help so far guys

 

[koalar]

Does the 100HP have a MAF

standard 1.1 and 1.2 run fine with the air filter removed. Even a small leak between the throttle body and inlet will be detected by the MAP sensor (post throttle body) causing the ECU adjusting the throttle plate angle or ICV. As long as there's enough adjustment left you shouldn't notice any problem

As a general rule. The only place that causes big problems via an air leak on the 1.1 and 1.2 is post MAP. Between the cylinder head and inlet manifold and only ones I know that fail here are engines that have over heated.

I believe there might has been a cracked inlet after an accident. But might have make or model mixed up it was a fair few years ago

1.4 is the same screen shot below

 

[Popitinpete]

I've got half a can of carb cleaner so I'll give that a spray around the inlet side

No work done recently apart from a cam belt change. Are there many pipes to look at for vacuum leaks? Agree it does feel like there may be a leak somewhere. Just wish it wasn't so cold and wet at the mo otherwise I'd be out there now

Thanks for the help so far guys

OK, did this problem start directly after having the cambelt done? Or was it OK for a time after the belt change then started?

 

[Wazzzer]

I didn't notice it straight away; car still pulls ok it's just low down revs, almost feels like it's in the wrong gear

 

[Popitinpete]

I didn't notice it straight away; car still pulls ok it's just low down revs, almost feels like it's in the wrong gear

Poss timing one tooth out? Could you go back to whoever did it and ask them to recheck? If you did it yourself worth a quick look at the timing again ( with timing tools)
It's one of those where it could be a couple of things. I would next look at timing after finding no air leaks.
Incidently the cheapo MAP sensor I had recently off fleabay a short while ago put my EML light on (mines not a 100bhp though)
Put the old MAP sensor on see if it changes things?

 

[koalar]

lets start at the beginning

engine idling, car in neutral, If you slowly raise the revs. do the revs raise as soon as you touch the throttle

engine idling, car in neutral. if you stab at the throttle a few times. Does it raise smoothly and drop back down. or does it bog down then raise

What state was the MAP sensor, covered in gloop ?

 

[Wazzzer]

The map sensor was a genuine Bosch unit and was surprisingly cheap so I changed it anyway, seeing as it looked to be the original 12 year old item. No gloop to be seen, just a mist and smell of fuel which I assume to be normal.

I haven't got the car with me today but once I'm home I'll have a quick check of the things mentioned above. Checks without sports mode activated?

 

[DaveMcT]

Check it with and without Sport mode.

 

[Wazzzer]

Well it's been a while but I may have cracked it...

I was fumbling around with something in the footwell and came across the clutch switch. Out of pure desperation I unplugged it as I know they can be a pain on the VW/Audi platform and it has cured the jerkiness at low revs!

To say I'm happy is an understatement. I was rewarded on sorting my problem by being driven into by a Range Rover

It never rains but it pours...