Idle speed

Following the radiator and hose (and brake pad) replacement, the cold idle speed dropped significantly and the car would only keep running when some throttle was applied. The revs would drop to 500 ish and then stall.

After 30 seconds it would idle by itself, but still a little low until warmed up. Where the idle was 750 to 800. It seemed strange that this had started right after collecting the car.

After contacting Dom at TVR Power, he said to bring it in and he would get it sorted ASAP. Some info from other users with this sort of problem that I looked at before the car went in is here and here.

The drive up was fine (after getting the car started), and Dom asked a chap I hadn’t met before, Wayne, to connect a laptop to the diagnostic port and see what was going on.

This port is in the driver’s footwell, above the throttle pedal.


There seemed to be an imbalance between the 2 sets of cyclinder (1-3 and 4-6).

Large difference between Adaptive 1 and Adaptive 2 (18.1)
Large difference between Adaptive 1 and Adaptive 2 (14.9)

I don’t really understand what the Adaptives do, but it indicates an imbalance in the throttle body settings between the 2 sets of cylinders. The numbers should be no more than 10 apart (those images show 18.1 and 14.9), and I think the closer the better.

Wayne removed the top of the air box, and did some tweaking of throttle body adjusters.

Throttle bodies, and a large air filter
Work in progress
Useful bonnet pins

After some tweaking, the adaptives were much closer and the throttle bodies balanced.

Adaptive 1 and Adaptive 2 are closer (3.1)
Adaptive 1 and Adaptive 2 very close (0.0)

After this something was reset and the adpatives went close to zero.

Wayne then started work on a problem with the lambda sensors. On a time-plot of lambda vales he thought they were being a bit slow to respond, and suspected a problem with the common earth for the sensors. This may be shared over a number of engine sensors, I am not quite sure.

Wayne pulled some sensor while asking me to watch the water temperature readout on the laptop. When he pulled the sensor, the water temp jumped by 3 degrees. This indicates an earthing issue.

The lambda sensor leads were modified so that a new and separate earth was created for them, and attached directly to the timing chain cover.

New earth connector created
Connected up, but before tidy cable-tie fixing

The work was finished off with cable ties to keep the wires against that pipe. Waybe trimmed the ties then rotated them downwards to that the sharp ends wouldn’t catch the hands of people working on the car. I hadn’t thought of that.

With that done he checked the response of the lambda sensors again, and was happy that they were rising and falling more quickly when voltages were viewed against time.

When I started the car, the idle felt notably smoother. I guess better balanced throttle bodies can do that.

The cost for 75 mins of labour? Nothing. Even though the idle problems were completely unrelated to the work Dom’s chaps had done, he fixed them for free. And as I was discussing my coming road trip and things to take with me, also included a 125 amp fuse.

I am happy with that 🙂

I’ll update after a few cold starts to comment on how it is behaving.