Rough Idling HELP!!

[ozzie]

So far to try to correct this problem I have invested in new spark plugs, distributor cap, rotor arm, HT leads(lumention) and cleaned the stepper motor (there was alot of carbon in there! thanks for that hint guys)and the air filter. Unfortunately it is still rough at idle, maybe I am expecting too much of my engine but the way I see it is that the more cylinders the smoother the engine - am I wrong? - it seems to shake at idle and when held at a higher RPM the pitch varies slightly (ie the rpm varies). The other ideas I have are that I have a dirty/mis-connected/broken lamba sensor, or my ignition timing is screwed. Please, Please share your experience and/or thoughts, because soon I am going to have to take my baby to the nasty dealer who will no-doubt replace everything and charge the earth!! Any help greatly appreciated, Thanks. (97P 450 Chimp, rough hot and cold, idles at 1050ish RPM)

[fordy]

Is the idle speed snaking around - if not then that would suggest the stepper motor is doing its job. Maybe worth checking the speed sensor on the dif - the ECU uses this info (along with the throttle position sensor) to determin whether you are sitting still and need the engine to idle - or whether you are moving with your foot OFF the gas - i.e under engine braking - if your under engine braking the ECU shuts off the injectors, to make the engine braking more efficient and to save fuel - i have heard of rough idling probelms being caused by a duff speed sensor - is the speedo working OK - on the later cars, the speed sensor also feed the speedo, so its easy to tell if its working OK. Another thing is the airflow meter - most TVR garages will swap this over with a known good one to see if it solves the problem - if it does your looking at £250 for a new one!!! Lamda sensors on the exhaust are also one to check - they are prone to breaking due to the serious amount of heat they contend with. good luck.

[ozzie]

Where exactly is the speed sensor on the diff? the speedo is working fine unfortunately! but I want to check it anyway. The idle speed seems okay after getting warm. Thanks for your help Edited by ozzie on Tuesday 5th June 18:16

[fordy]

Not sure exactly where abouts on the diff the sensor is - as far as i know its the only sensor on there - so it should be reasonably easy to find some wires coming from it. Another thing i forgot to mention was dirty injectors - if one or more injectors is slightly blocked, then your idle will seem rough - you could try some injector cleaner in the petrol. good luck. If you eveuntaly solve the problem, would you mind posting back here to let us know what it was - its always useful to know these things. cheers Chris

[ozzie]

Sure let you guys know the answer for my problem, but thanks for the ideas.

[ozzie]

Well...update - I have just spoken to Mole Valley and had an indepth conversation with the parts chap....he reckons it is either the Lamba sensors, water sensor or idle sensor, but way to tell is to link my baby upto a fancy laptop....will do this next weekend, then I will tell all and reveal this mistery.