stalling

[Pinkney]

I am taking the car in for it's next service (36k) on Wednesday so the following problem will be looked at. However I would like to know if anyone out there has has had the same problem and if so, knew what might be causing it.

Whilst in stationery traffic (temp @ 90-95º) the revs occasionally drop below 1000prm and engine stalls, if however, I rev the engine up to 1500-2000rpm before it drops below this mark the car then settles into idle at just over 1000rpm and seems OK. However as I prepare to move off and depress the throttle slightly the revs then drop below 1000rpm, oil pressure drops and engine stalls. The only way to move off without the car stalling is to rev the engine to 1500-2000rpm as I move off. Although this makes for a few grandprix starts everyone is under the impression I'm wanting to race as I am constantly revving the engine before moving off !

The car is running slightly lumpy at low revs but after 2000rpm settles down nicely. This has only began happening in the last few days. I run the car on 97Ron/Optimax and never on unleaded.

Cheers

Dan

[anonymous-user]

Could be fluctuating Throttle Potentiometers. Had similar problem on my Cerbera.

They were spiking all over the place and caused dodgy idle speed and lumpy ride at low revs.

Dealer spotted problem and replaced offending items.
Don't worry, they're not too expensive !

[mycerbera]

Had same problem at the weekend under 3000rpm!
Steve from Thames Valley was on hand at Castle Combe TVR Track day with his laptop and adjusted them. Now it runs sweet from 0-7500RPM!

[Pinkney]

quote:
Could be fluctuating Throttle Potentiometers.

Huh

Cheers Guys,

I'll mention these to the Garage on Wednesday (whilst making it look like I know what I'm talking about!)

BTW what are these and what do they do? - might as well learn something about these cars.

[dannylt]

Try searching this forum for "throttle pots" - there's quite a bit of info been posted. Basically it tells the ECU how open the throttle butterflies are, and from that it calculates how much fuel to inject, and when to fire the ignition. When you move the throttle quickly, it also adds extra fuel - acceleration enrichment. If the sensor is noisy, this will fool the ECU into dumping fuel which generally makes the engine unhappy.

[dyb]

Probably just needs a tune. It's wise not to wait until you actually need a service as they will deteriorate over a short time, especially if left standing for a while. I usually pay about £45 for a quick tune every 3,000 miles. Another thing is a cracked manifold, they are common.

[leszekg]

Had very similar symptoms on my Cerbera about a month ago. Turned out to be one of the throttle pots was faulty. About £30 for new part plus half an hour labour. Get a dealer to run the dignostics on your car which will quickly tell you if this is the cause of the problem. The function of the throttle pot is a bit like the hand throttles on a Scalextric set, and the design is almost as crude. Deposits can build up on the potentiometer over time resulting in poor or incorrect readings being passed to the ECU. The result is usually lumpy performance and/or a kangeroo style drive. Judging by the frequency that this problem seems to pop up among TVR owners, I'm almost tempted to carry a spare one!

[Beej]

Just a little tip on throttle pots.. they are Escort Zetec items, so you don't need to pay TVR prices if you need replacements. That being said, they are not that expensive in the first place. The problem is, you need the MBE software to set them up and I'm still working on that one.