kangaroo S2

[lewdon]

Has anyone else experienced a fault like this on a 2.9 S2. I don’t want to start replacing components at random, so any advice will be very gratefully received.
After driving at a constant speed (usually in a queue of traffic at about 40) for a little while the engine suddenly starts to misfire and looses power. Push the throttle down to try to maintain speed and suddenly the power comes back and the car leaps forward. We kangaroo down the road for a minute or so and then it clears as suddenly as it came.
It only occurs about every 40 or 50 miles (always in the dry) and usually lasts less than a minute, so I haven’t been able to stop and open the bonnet while it is happening.. But it is most unpleasant while in progress.
I have been unable to replicate the fault in the garage despite much wire wiggling. I refilled the tank at a different garage in case there was water in the fuel and I’ve checked and cleaned all the electrical connections I can find around the engine including the multipin connector hidden under the coil, I have also cleaned the airflow sensors with carb cleaner and checked their flaps move smoothly.
I have now run out of ideas, so, Oh Wise and Knowledgeable Ones, can you please advise what should I try next or replace first. Thanks.

[S2Mike]

Vaguely similar symptoms on mine. I found the screws on the dizzy cap were loose . Worth a look, or loose HT or LT cables on the coil or spark plugs. In the damp the spark might still get to its destination.

[phillpot]

Bit of a "long shot" but check the two big air hoses between the AFM's and the engine for leaks, and the vacuum pipe to the servo, in fact while you're at it check the bottom of the servo for rust holes.

[Griffinr]

Start with the simple stuff, disconnect, clean and apply Vaseline or a proprietary electrical grease to all the connectors you can find under the bonnet. Also check whether you still have the yellow connector on the steering column. Earth faults are also common so clean and grease those as well. If you still have a problem then move on to component checking.
Rob.

[GreenV8S]

I never had these symptoms on my S2, but I've had very similar symptoms on the V8S several times. The most common cause was a worn throttle pot and in hindsight it makes sense that it would tend to wear out around the 'cruise' position. I also had several unrelated problems in the fuel pump electrics that caused this to be intermittent: the main power relay, the fuel pump relay, corroded and loose sockets for both relays, faulty wiring to the inertial cut-out, corrosion of the inertial cut-out, broken wiring at the pump and poor connection to the pump terminals. Finally, of course, the big yellow connector in the steering column.

You can check whether it's a fuel pump supply electrical problem by bringing power from the pump back to a small bulb in the cockpit where you can see it.

[lewdon]

Thanks everyone. I have taken all your advice.
S2Mike, i have had the dizzy off, cleaned it out, replaced it and tightened the screws carefully. I have checked HT/LT connections and run the engine in the dark to see any stray sparks. Nothing untoward found.
Phillpott, I’ve checked air hoses, vac hose and servo. No leaks found.
Griffinr, i have cleaned all the contacts, earth connections and connectors I can find. I still have the yellow connector but I have cleaned the contacts on this and checked that the resistance across each contact is approaching zero. There is no sign of it getting hot so, on the basis of “if it aint bust don’t fix it”, I was going to leave it for the moment. Testing the sensors themselves is probably a bit beyond me so if it comes to this it is probably a garage job.
GreenV8S; I have tried cleaning the relay connections but they are very hard to get to, and I’ve given all the wires a good wiggle, I’ve tried opening the throttle very slowly by hand and can’t find any point where it seems to miss, but without the engine under load I reach max revs long before full throttle, (I’ve tried doing it with someone slipping the clutch against the brakes but not a very satisfactory test). I think I will change the throttle pot as they are cheap and if that doesn’t work i’ll take it to the Garage. (by the way, what is an inertia cut out please, and where would I find it?).

The problem is that the fault only occurs so intermittently and I don’t fancy paying the mechanic to drive around for 50 miles waiting for it to happen. I believe the main clue must be that it only seems to occur after a period of driving at near constant speed – if I could only work out what the clue means.

Once again, Thanks everyone, your suggestions have been very much appreciated, and if anybody has any more ideas please let me know.

[phillpot]

lewdon said:

what is an inertia cut out please, and where would I find it?

Inertia switch example
Not fitted as standard to V6 engined cars as far as I know.

[Roy C]

phillpot said:

lewdon said:

what is an inertia cut out please, and where would I find it?

Inertia switch example
Not fitted as standard to V6 engined cars as far as I know.

Don't look for it - TVR never used it with this engine.

Have you tried unplugging the Throttle Pot?

Another problem that can cause similar problems is failure of the fuel injection multiplug that sits in the vee on top of the engine (and cooks).

[NeilS3]

Roy C said:

Don't look for it - TVR never used it with this engine.

Have you tried unplugging the Throttle Pot?

Another problem that can cause similar problems is failure of the fuel injection multiplug that sits in the vee on top of the engine (and cooks).

The first thing that came to mind while reading this was the 'Throttle Pot' an easy fix though, loads of old threads about it.

Regards

[lewdon]

Thanks everyone, advice very much appreciated.
I'm now going to order a new throttle pot (Motoquip part No VTP103, £32-26 inc Vat from "parts for all cars") which I hope is the right one.