Im sorry to say that today the car was back to its old hunting self.

@TrentBarton i looked at replacement throttle body’s also but I was thinking of going down the route of a secondhand unit, my thinking being that it would be better quality. The thing that’s holding me back from doing it is if the ECU does need to be reset I won’t be able to.

Sorry to hear that @Rsedmonds . Your big discovery led me to looking at my negative connections to the block but they were all in good condition so no quick fixes for me either.

Do you really think the ECU will need a reset with a new throttle body? My manual does not suggest it does. See Section 6 below. I thought just a battery disconnect after replacement would do it (see the smaller screengrab below).

I'm sure I've read that somewhere and when i get time ill try to find what i read out.

I suppose that disconnecting the battery makes sense and could have possible cleared my initial issue in the ECU making me think that it had gone away. Then having a bad (assumed) throttle body the issue soon came back.

I think that i might remove the throttle body next to clean it and see where that leads?

That sounds like a good idea. I've given mine a clean in-situ but not been bold enough to take it off yet and clean properly due to fear that there might be a gasket under there, and in the absence of an off the shelf replacement, might have to make up a new one with gasket paper.

However, after some more research and speaking to a few friends with old VWs, I am pretty sure it is just the ring seal described in the Haynes manual above so time to be brave, take it off and give it a really good clean as you say, hope the ring seal doesn't disintegrate in the process.

5 hours ago, TrentBarton said:

However, after some more research and speaking to a few friends with old VWs, I am pretty sure it is just the ring seal described in the Haynes manual above so time to be brave, take it off and give it a really good clean as you say, hope the ring seal doesn't disintegrate in the process.

The O ring is available for £10.50 with P+P on LLLparts and measures 52x2. You can get an equivalent from eBay for around £4.

10 hours ago, TrentBarton said:

Do you really think the ECU will need a reset with a new throttle body? My manual does not suggest it does. See Section 6 below. I thought just a battery disconnect after replacement would do it (see the smaller screengrab below).

not 100% sure as I’ve been looking for the article I read originally and can’t find it. I did find the like below which take you through the reset process in VCDS thoughts 🤷🏼‍♂️

http://wiki.ross-tech.com/wiki/index.php/Throttle_Body_Alignment_%28TBA%29

Interesting. I wonder if the reset process through the OBD has the same effect as the battery reset.

Well, I've ordered my seal, thank you for the link. I am abroad for a couple of weeks from Monday but if the seal arrives before then I will give it a go and let you know the results.

In case you need it for your one, the throttle body mounting bolt torque wrench settings are 10nm according to Haynes.

Thank for the toque setting they came in handy.

I’ve removed the throttle body this morning and gave it a good cleaning on the outside firstly with a degreaser, secondly with brake cleaner moving the brake cleaner to the inside of the throttle body and finishing off with carb cleaner. Considering it looked clean my rags were filthy. I also noticed that where the flap meets the body there was quite a bit of pitting ( obviously from its life on the farm). There is also what I assume to be an air temp sensor on the side that I removed and cleaned while I was in there.

I’ve now had the car sat on my drive for over 40 minutes now ticking over (haven’t tried any throttle yet) and it’s started up at 1200rpm and dropped to around 900-950 where it’s sat now. It’s completed about 6 heat cycles in that time and the cab is lovely and toast.

I’m Not saying it’s sorted yet as it’s early day but it’s running far better than it ever was. I also checked my fuel filter and it doesn’t look like it’s ever been changed so that’s next on my list.

A lot of servicing and maintenance and many repairs boil down to clean and lubricate. An engine oil and filter change is a form of clean and lubricate. An ECU reset by OBD or battery disconnection is a form of cleaning the electronic systems. Mechanics often make out they are doing more complicated stuff than this and many times they are - and many they are not and it boils down to clean and lubricate.

Good luck.

Edited 22 February22 Feb by nta16

@TrentBarton

Hi mate,

how are you getting on with your erratic tick over?

My car isn’t on the road as yet but I have been able to give it a sneaky run and it seems OK.

I’m not closing the case yet as I do t feel I’ve proven it out thoroughly yet but the signs are good.

I do now have another issue where Its running a little hot that I’m focusing on first so watch this space.

Hello @Rsedmonds

I've just got back yesterday from working abroad for a couple of weeks. I have the tools, cleaner and new ring next to the car in the garage, ready to give it your treatment this weekend so I will let you know how that goes. Keep me updated on your end. Glad to hear that it is still looking good.

Did a lot of cleaning this morning and put it all back together but sadly, still getting rev hang and a some strange idling. I am going to order a new throttle body today and hope that a new throttle position sensor within the body will solve the problem.

New Lucas throttle body today but still getting intermittent rev hang and slightly odd idle.

An interesting part of the rev hang is that it stops the moment I touch the clutch or brakes. My understanding is that when you slowly lift your foot off the accelerator, the TPS sends a signal to the the ECU to gently reduce fuel input so you don't have a sudden jolt effect. However if you touch brakes or clutch to change gear, it drops fuel more rapidly to idle level. However, what I seem to have is that the the ecu is holding the fuel input longer than it should, unless I touch brakes or clutch which instantly overrides and says 'drop fuel now'.

Separate to this, I had an issue the other day when it was raining very heavily and the revs went very erratic and the car stalled. This had led me think about possible earth/ connection issues.

Decided to sit and look for voltage drop between the -ve on the battery and the engine block to see if there is a bad earth that might be causing a messy signal between the TPS and the ECU. At idle I am getting 0 volts most of the time but very occasional flicks up to 0.2 or 0.3 volts for a second or less every minute or two. I might be grasping at straws now but perhaps this is giving me the problems.

So next step, I will get under the car and have a look at the strap from block to chassis. Any advice on known troublesome earth connections and locations would be very much appreciated.

12 minutes ago, TrentBarton said:

This had led me think about possible earth/ connection issues.

. . . but very occasional flicks up to 0.2 or 0.3 volts for a second or less every minute or two.

Check wiring and connectors/connections are all clean, secure and protected (and so water don't get in). Loose or corroded connection(s), frayed or corroded wires unseen inside their insulation, often seen starting at a connection/connector but can be at other points in the wire(s) particularly if the wire(s) are unsecured where they should be secured and/or rubbing or trapped or caught against something.

Edited 18 March18 Mar by nta16
missing word

On 18/03/2026 at 21:26, TrentBarton said:

An interesting part of the rev hang is that it stops the moment I touch the clutch or brakes. My understanding is that when you slowly lift your foot off the accelerator, the TPS sends a signal to the the ECU to gently reduce fuel input so you don't have a sudden jolt effect. However if you touch brakes or clutch to change gear, it drops fuel more rapidly to idle level. However, what I seem to have is that the the ecu is holding the fuel input longer than it should, unless I touch brakes or clutch which instantly overrides and says 'drop fuel now'.

Separate to this, I had an issue the other day when it was raining very heavily and the revs went very erratic and the car stalled. This had led me think about possible earth/ connection issues.

Decided to sit and look for voltage drop between the -ve on the battery and the engine block to see if there is a bad earth that might be causing a messy signal between the TPS and the ECU. At idle I am getting 0 volts most of the time but very occasional flicks up to 0.2 or 0.3 volts for a second or less every minute or two. I might be grasping at straws now but perhaps this is giving me the problems.

I didn't find any connection from brakes to ECU. The clutch is even weirder, it's entirely mechanical, there's no electronic sensor at all.

Brake could be explained by some air leakage from the booster, but I have no idea how clutch could have any effect on the engine, besides small load change from the gearbox.

Weird idle and misfires during rainy weather was caused by bad ignition module on my 1.3. but those were notorious for failures, I'm not sure if the 1.6 had similar issue.

Hey @Papez

Thank you for checking. I had also gone through my workshop manual and struggled to find any direct electronic link between clutch/ brakes and ecu so good that you have clarified this. It must be based on a load change I suppose. It is very unusual, I have taken the issue to a couple of garages and to some friends who are more knowledgeable about mechanics than I am and have not found an answer yet. Perhaps a strange niggle in the ECU itself?

I have cleaned all on my earth connections. I have also replaced the vacuum pipe and check valve to the booster. The issue remains! I have to replace my rear brakes soon anyway so might do the booster at the same time and see if that helps.

Failing that, will start looking at ignition system!

When you say you cleaned all earth connections is it all of them as there can be a lot all over the car. Then you need to check the connections (and wires) with a meter whilst wriggling them. As it clutch and brakes it's weird but I'd check the power and earths to brake lights, the switch, the connections even remove the brake lights bulbs and check them. Perhaps even replace the bulbs but with good quality manufactured bulbs, or long life or whatever term they use to suggest they're not cheap crappy made bulbs that so many are.

I have no idea of the pedal set up on your car but if both clutch and brake pedals are on a shared bar to hang from that one area of commonality and if the brake light switch is there too that's a second area brake of commonality, if so I'd have a good look and testing of that area, making sure everything it secure and operates as straight and freely as it should and that the brake light switch if located there isn't in someway interacting with mechanical operation of pedals when it shouldn't.

I have found electrics can act very strangely and unexpectedly even on cars with much, much less and simpler wiring and connections (and no electronics at all, imagine that if you can).

Trying to push the clutch pedal by hand with really give you an idea of how "heavy" or "light" feels. 🙂

Good luck, and remember, checking, double and treble checking is often better than changing, and less cost.

On 15/04/2026 at 09:50, TrentBarton said:

The issue remains! I have to replace my rear brakes soon anyway so might do the booster at the same time and see if that helps.

What if you just plugeed the outlet to the booster and try if the issue persists? (not while driving, ofcourse!)