Car Still Not Right

[Mark W]

After a few issues with my GS430 its still not right....Engine mgmt light came on a few months back and car running a little rough...indicated 02 sensor prob and had both pre-cats replaced.....

Seemed to be ok for a bit but progressively getting worse....intermittent rough idle, intermittent loss of power when accelerating (seems to have no go, then will fly along - but this is also intermittent).

At idle, the car sounds like missfiring when stopping at junction - but only happens after stopping for about 5 seconds or so usually - and not all the time. Revs tend to drop to ~400 at times too - again not always.

When car is running rough I actually get vibration in the car when driving.

I had to put in high octane petrol the other day as petrol station had run out of normal....car ran as smooth as it has for ages.

Kept on using the high octane fuel for the next few fill ups - but problem gradually creeping back.

The really strange thing is - If after driving the car for a few miles, I then stop - wait for 5 minutes - and then start her up again, shes as smooth as anything for about 10-15 miles....then problem tends to return.

The symptoms are sort of similar to those I had with a Vectra I once had - new Idle control valve and throttle body clean did the trick. Not sure if this is worth a try.

No DTC codes and also had the electrics checked over by auto electrician.

Any ideas ?

[Mike_B]

I wonder if the throttle position sensor is playing up? That could explain the intermittent acceleration issues and also the rough idling...

[randyreindeer]

I have just noticed this thread just as I was about to post something similar about my GS.

My car has been playing up for a while now but I put it down to lack of use. (just on 1800 miles in 2 years). The emission side of it only just scraped through this years MOT so i had to investigate. I had no fault codes showing or any difficulties in starting the car. It idled fine but would miss fire every so often and on acceleration it would surge as if it was dropping a cylinder and then firing on all six. This happened very quickly so it wasn't as if the same cylinder was dropping off. Eventually the missing cylinder turned into a backfire.

I cleaned the plug leads, The Dizzy Cap, Connections to the Injectors, ran Injector cleaner, new plugs, cleaned Throttle Body, Compression test hot and cold, changed Fuel Filter, scratched my head, checked dizzy and rotor again, cleaned leads, tried substitute leads and a Substitute Rotor arm.

Yep. The Rotor arm. It looked fine but changing it cured the fault. I put it under a cheap and cheerful microscope type thing and could see a hairline crack in it which was causing the spark to arc.

Now the car is back to its good old self and i'm taking it back to the MOT place just to see how much cleaner its running.