cerbie jumping at very small throttle openning

[ancol]

hi guys just back off hols to wales was missing driving the cerbie so left the missus there and came back early to have a drive of the beast oh well you have to get your priorities right.had 4.2 cerb ajp eng approx four weeks and have noticed car jumps slightly at very slight throttle opening ie when trying to drive at correct speed limits albeit very difficult when you really want to open it up anyone else experienced this problem regards andy cole

>> Edited by ancol on Monday 29th August 23:26

[petros]

Same problem with my Chim and still trying to isolate the cause.

[ancol]

thanks for reply petros someone said may be throttle linkage and modified linkage may solve the problem maybe some other gassers out there may know in anticipation andy cole

[kojak]

might be the throttle pots.

[mad mark]

I had a similar sounding problem with my Cerb 4.5. Austecs diagnosed that the Throttle bodies had come loose. Also I've heard of loose manifolds causing similar sounding problems.

[cerealsurfer]

Just had exactly the same problem and ended up with a "B" bank throttle Pot. Also found that both distributors were cooked after a summer's fun as were the leads.

Any one of these can give you the characteristics you describe.

Also Lamda Sensor can make a difference. These are prone to going. (Had this problem a little while back)

If it's a throttle pot you'll notice one bank emissions are a little off. When you start the car on a cold day take a look.

[marcus1970]

My Cerb 4.5 is the exact opposite. Gentle acceleration and she purrs along sweet as, right up to 7500. However put your foot down and she coughs and jumps and takes ages to get going.

Regards MB

[mikesr]

You should check the adaptives and throttle setup with the diagnostics prog. Also log the throttle pot readings whilst driving. Big spikes in the throttle pot values are an indication of a 'noisy' pot that will need replacing or electrical noise interfering with the signal.
Check the balljoints on the throttle linkage. If there is lots of play they need replacing. This is a big cause of eneven running as the throttle is opened and closed during about town cruising. The diagnostics will also show any faults on lambda sensors etc
The throttle pot readings and adaptive percentages should be about equal. There is a thread from Joo describing how to do the setup - do a search for throttle pot.
The other cause of rough running that I experienced was filthy connections on the coolant sensor. The resistance was varying across the plug contacts and producing some really wild swings in the coolant temp reading (from 10 to 30 and everywhere in between). Again the diagnostics will show this if you log the sensor readings whilst driving.

>> Edited by mikesr on Tuesday 30th August 14:30

[ancol]

thanks for all the feed back guys dont know whether to laugh or cry was hoping some of you would come up with a few things that could be causing the problem now ive read them all i now know it may be harder to trace but anyway many thanks. now excuse me for sounding a bit thick on this one but am not sure what the throttle pots actually are or look like and also how does one diagnose various possible causes whilst driving i know you say plug in diagnostics but where are they available from or would it just be better to take it to a specialist. im not green to working on cars as my previous pride and joy was an mgb which i have owned for past thirty years and carried out a full nut and bolt restoration on but i must admit the technology of a tvr is a lot more intricate sorry for the essay chaps but thought id give you the full picture

[cerealsurfer]

Best to take it to a specialist.... TVR AJP V8 engines are Formula 3000 based and similar technology to the 80's Jag Le Mans V12 prototype engines.

And they are considerably more difficult to get running right than a MGB motor. TBH. best left to the experts, saves money in the long run.

[Nickccc]

Ancol, you are based in the midlands.
That's Track Car country, Give joo a bell and see if he can fit you in. Seriously I have recently got my Cerb back it's like a new car.
You could have any number of possible probs, have you got the software, that would be a good place to start. Take a look at the Final rolling road thread.
I had problems that the dealers could not even diagnose.(sp)

Nick.

[Pete Cash]

Ancol,

I had exactly these symptoms in the past, but now she runs perfectly smoothly - if it's any use to you I can recommend Mike @ Horizon Motorsport ( in Cradley Heath)who looks after mine & I believe several others on here - he's an ex tuscan race engineer so knows his stuff. He has certainly sorted mine out 100 times better than the franchised dealers.
Pete

[RUSSELLM]

Before you spend too much looking for complicated answers, can I suggest you get the throttle cable checked.

I put up with what you did for months until the cable finally snapped.

Couldn't beleive it after it got replaced, like driving a different car.

Yours could be frayed, as you push the pedal you take up the slack, push it a bit more & the car lurches forward,

Hope that helps.

[ancol]

thanks for all the advice chaps will get specialist help like you say will probably work out cheaper in the long run