uneven idle and stalling

[keithTVR350i]

Is this a common problem ?
My 350 wedge is terrible for its uneven idle, on start up she is happy at 1250 rpm, however when she warms up the idle drops to 900 rpm and then will die.
I have turned up the idle via the allen headed screw on top of the throtal linkage, but this still leaves me with an uneven pattern (from 1200 rpm down to 500).
It is potentially dangerous, any advice ?
Thanks Keith

[danny hoffman]

Well where shall we start!

I would suggest checking for any air leaks on the inlet side, also the overun valve which I know some people blank off completely. Then check all wiring, earths etc and don't forget the big connector on the ECU under the glove box.

Whilst you are in there, if you are handy with a soldering iron, it would be well worth resoldering all the dry joints in the ECU - however if you are nervous of damaging it put this at the bottom of the dianostic list.

Also check all the sensors/flapper box are working properly, there are diagnostic procedures in the Haynes SD1 manual. If the idle is lumpy you may have a drippy/blocked injector and some cleaner may improve things.

I went through all these trying to diagnose a problem that turned out to be a worn cam, but they all improved the running of the car slightly.

Danny

[mrcrappy]

have you fitterd one of those adjustable fuel pressure regulators, my car started idling badly and i found the fuel pressure was nearly 3 times what it should be (36psi) i had the car int 3 tuning " experts" and had it rolling roaded and none of them could find out what it was, in the end it was the last thing i could think of checking.

[keithTVR350i]

Hi Danny,
I have been checking for vacuum leaks, the biggest one so far is the actual throttle ajustment hole, I removed my allen key and stuck my finger in the hole and it was difficult to remove there was so much 'suck'. Idle has improved.

Are ajustable fuel pressure regulators not a sensible buy then ? I have recently ordered one from a RPI, (not fitted yet), they assure me it will improve overall running of the car. Anyone tryed one ?

[shpub]

See the engine mod section on www.t-v-r-services.co.uk. Story of what happened on my 390SE with one.

[danny hoffman]

I presume you mean the idle adjustment, mine has a slotted screw not a hex?

Danny

[keithTVR350i]

Hi Danny,
Yes the idle ajustment screw/allen headed screw(on my mk 2 version ?) was badly leaking, running better now plugged.
Cheers Keith

[2 Sheds]

If your idle problems persist its worth checking the throttle pot position, but you need a digital multimeter with thin probes, with the ignition on and the throttle closed, measure the voltage by pushing the red probe of the meter into red wire on the throttle pot connector and push the black probe into the green wire, you should have a reading of 0.32-0.34 volts.
The adjustable fuel regulators are a good idea, as it gives a fueling adjustment without modifications to the ECU, I have seen a 350i pick up 5 bhp !
Tim

[Brm Brm]

Hunting at idle is often caused by a dodgy or coked up stepper motor so recommend you check that too!

[danny hoffman]

My 350i is too old to have a stepper motor, in fact I am not sure any wedges did (I stand to be corrected)

Danny

[Brm Brm]

Well, I dont know what year they were introduced but my previous 400 (1989) had one (cos I changed it to cure hunting at idle - it worked) and my current SEAC 1988 has one.

[2 Sheds]

Stepper motor is on the hotwire cars Early 1990 onwards, 350i were all pre hotwire/ flapper, later 400's/450's and later SEACs were hotwire, the flapper injection cars 350's 420's etc had a cold start valve which looks similar to a stepper motor, but only operates when cold and does not normally fail so don't bother cleaning it.