Really random idle revs

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Stan Thomas
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Re: Really random idle revs

Post by Stan Thomas »

Just a thought - but have any of your vacuum pipes gone "soggy".

I say this because we had a similar problem to yours and it transpirered a soft vacuum pipe was sucking "closed" when the engine was running but appeared O.K. when the engine was stopped.
lsowden12
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Re: Really random idle revs

Post by lsowden12 »

friend of mine brought up a very good point. The first time this started happening was the day after I was testing for a battery drain and was consistently disconnecting and reconnecting the battery all day. He thinks the ECU got confused and has forgotten to program the right air fuel mix ratio. I have disconnected the battery entirely and will leave it off overnight and see if that resolves anything. I will also try the brake cleaner trick tomorrow if not :)
1994 Rover 214SEi - Nightfire Red / Tempest Grey
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g259fsg
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Re: Really random idle revs

Post by g259fsg »

Had this problem on our 214 GSi after it had been in the garage for a head gasket change. Idling was somewhat erratic, although it was initially fine when I collected the car. Took it back to garage, and the mechanic (an ex-Rover guy) went straight to the vacuum tubes. One goes to the MAP sensor on the ECU, but it was the other one which was the culprit. It goes off the manifold up to an air temperature sensor/valve in the air filter and then over to a flap arrangement in the air intake to switch to warmer air off the exhaust manifold. Don't think any of that works now, but the mechanic found one of the vacuum connections was loose. Fixed the problem immediately. I did fit some new tubes later to be sure and it has not re-occurred. Don't know if your car has this, being a later model, but you could block this tube at the manifold to see if the circuit is causing trouble. If air gets in, it destabilises the mixture and the ECU starts hunting. Make sure there aren't any other air leaks round the throttle body.
1990 Rover 214 GSi (VIN 222977)
1964 Humber Super Snipe Series V
1965 Humber Sceptre Mk.1
1966 Hillman Minx Series VI
crepello
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Location: Herts

Re: Really random idle revs

Post by crepello »

Thought: Do vacuum non-return valves to the brake servo fail sometimes?
lsowden12
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Re: Really random idle revs

Post by lsowden12 »

Some really helpful ideas on this one. Figured I’d update.

Disconnecting the battery under the assumption that the ecu had confused itself did actually initially fix the problem for about 2 days then it started again. Tried to smoke test the car and as far as I’m aware I couldn’t find any leaks. I am going to be replacing both the fuel filter and distribution cap this week hopefully to see whether that is related or not.

The fuel filter looks insanely rusty and I suspect it’s original and likely blocked and the car jumps around when you get on the throttle so perhaps it’s the cap that’s given in and it’s just struggling

Either way, for now, the car still revs all over the place. The motor seems to reset every time the ignition turns off too and I can’t remember it its always done that or not. That whirring clicky motor sound, happens every time you turn off the ignition. But it doesn’t just do it once it does it about three times with a period in between.
1994 Rover 214SEi - Nightfire Red / Tempest Grey
crepello
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Location: Herts

Re: Really random idle revs

Post by crepello »

When the ignition is turned off I believe the ECU is supposed to set the stepper motor to the
position it predicts is required for the next cold start, so whirring sounds normal. Three times,
I'm not so sure...
lsowden12
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Re: Really random idle revs

Post by lsowden12 »

wowee, this probably isn't related to the idle issue but the distributor sure as hell needed replacing, absolutely covered in oil on the inside and all the contacts are pretty much non existent at this point because they're so worn out

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1994 Rover 214SEi - Nightfire Red / Tempest Grey
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g259fsg
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Re: Really random idle revs

Post by g259fsg »

The contacts do look a bit moth-eaten but probably wouldn't affect the spark too much. The contacts look a bit eroded by the spark. Maybe an indication of a poorer quality component. Worth changing it and the rotor arm so you can hopefully eliminate it from the problem. BTW, are you getting a good spark at the plugs when the engine is hot? If you take out a plug and hold it by the cable, you should get a spark jumping from the hot end of the plug to metalwork 12-15 mm long. If it's a lot less than that, then there's a problem with the ignition leads or the rotor arm (or the coil).
lsowden12
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Re: Really random idle revs

Post by lsowden12 »

g259fsg wrote: Tue Feb 27, 2024 5:30 pm The contacts do look a bit moth-eaten but probably wouldn't affect the spark too much. The contacts look a bit eroded by the spark. Maybe an indication of a poorer quality component. Worth changing it and the rotor arm so you can hopefully eliminate it from the problem. BTW, are you getting a good spark at the plugs when the engine is hot? If you take out a plug and hold it by the cable, you should get a spark jumping from the hot end of the plug to metalwork 12-15 mm long. If it's a lot less than that, then there's a problem with the ignition leads or the rotor arm (or the coil).
Not sure but I can give it a go, I'm just going to replace absolutely everything I can within reason one by one until I figure out whats going on, eventually I have to hit the mark, the question is when. If the dizzy replace doesnt work then the leads are next up
1994 Rover 214SEi - Nightfire Red / Tempest Grey
Mr Teddy Bear
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Re: Really random idle revs

Post by Mr Teddy Bear »

Don't touch the H.T leads with your hands while the engine is running, use an electrically insulated plier if necessary. Otherwise you will receive a very nasty shock!
Teddy Bear

216 Sli SRS Charcoal Met 1996

214Si Silver? Tempest Grey 1993
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