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Rough idle


209MOR

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Thanks to the wealth of content on here I’ve done lots of research but most of the faults with idle issues seem to be either surging idle or rough idle when cold. Mine has neither - it starts and runs perfectly smooth when cold but after a run, it idles really roughly. I’ve also noticed a backfire when changing 2nd to 3rd and potential misfire. 

 

The list of potential injection and airflow solutions is endless so where should I start?

 

The car has done 80k miles and has no major work done to it as far as I know

 

TIA

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1 - check fuel pressures

2 - check for air leaks

3 - check Aux air reg is operating fully

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I guess normal things apply when misfiring

Plugs - when last changed, check tightness

Wires - Still on orginal, check for cracks and fitting snug

Coil - still on original?

Cap/rotor - when last changed

80k and if none of the above have been changed I would update them anyway for peace of mind for another good few miles.

Then as PeterK said, move onto fuel pressure etc and I guess if no major work done then perhaps some gaskets are in need of changing and air leak.

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Breather air leaks.  You may notice 3.2s rough idle when you remove the oil filler cap as its essentially a closed system.  If it makes no difference when warm and cap removed suspect the various breather hoses around the back of the airbox.  This will be somewhat masked when cold as it will be running rich during warm up.

 

Edited by Nige
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8 hours ago, Nige said:

Breather air leaks.  You may notice 3.2s rough idle when you remove the oil filler cap as its essentially a closed system.  If it makes no difference when warm and cap removed suspect the various breather hoses around the back of the airbox.  This will be somewhat masked when cold as it will be running rich during warm up.

 

Hi Nige,

I was thinking the same thing, as the problem seemed to resolve itself after the OP put oil in, thus re-seating the oil filler cap maybe ??? its the only posible explanation I can think of after the oil top up!

Edited by Ant7
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Hi,

 as you described a backfire, the first port of call is to check plugs/ignition wires have a good spark. If all is good, then check that the injectors are opening as they should ,eg with a stethoscope.

  As mentioned above the wiring of the Flywheel and Speed sensors fail over time, heat from engine will increase the resistance. Tough usually this causes a  car breakdown rather than a misfire Remove the nearside rear wheel, check the insulation is present on these wires.

 

                                                           

  

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Thanks for the tips - looks like a few areas to test at the weekend if I get a chance. Also noticed an oil leak from the vacuum switching valve (item E on Here) not sure if it’s related but might as well replace it once I find the part No.

 

 

IMG_5194.jpeg

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  • 2 weeks later...

Update 

It’s been a couple of weeks now and I think I’ve cracked it! Engine is idling smoothly now and runs well through the rev range 

 

Things I’ve checked and changed are;

 

  1. Cleaned up the idle control valve  - it was dirty and the piston didn’t move freely when shaking but that had no effect 
  2. Checked all hoses but no signs of any air leaks in the breather hoses
  3. Tightened up inlet manifold and most of the bolts took a 1/4 turn
  4. Changed the plugs, HT leads, dizzy cap and rotor. 
  5. Got the injectors checked and cleaned by Graham at injectorcleaning.co.uk - AMAZING service with quick turn around and very cheap. The report said they were in fair to good condition so I don’t think that was a factor really
  6. Stripped the mass air flow sensor down and there were definitely tracks carved in the carbon strip which would have affected the idle. With a slight adjustment of the circuit board position, the wiper is now running on a clean bit of track

 

So my guess is that it was a combination of the new ignition parts and the air flow sensor adjustment that resolved the issues. 

 

Anyway, absolutely delighted how this old thing sounds and drives now. By far the most difficult job of all was getting the top clip at the back of the air box on!!!!

 

My next thread will be about the blower motor not working! Oh the joys……

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The Blower motors on these old cars are a weak point for sure, I have changed a few on the car's I have owned over the years. In my opinon they are a very crude and fragile motor considering the price of these cars when new. I remember trying to repair the first one, unfortunetly the motor housing the brushes sit in is made of some form of plastic which obviously melts and distorts when the motor is being used for any length of time. There is an upgraded metal version that some have fitted, which looks to be a no brainer especialy as the motor is not the easiest to get to and replace, I will try and find a link and post it here.

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29 minutes ago, Ant7 said:

The Blower motors on these old cars are a weak point for sure, I have changed a few on the car's I have owned over the years. In my opinon they are a very crude and fragile motor considering the price of these cars when new. I remember trying to repair the first one, unfortunetly the motor housing the brushes sit in is made of some form of plastic which obviously melts and distorts when the motor is being used for any length of time. There is an upgraded metal version that some have fitted, which looks to be a no brainer especialy as the motor is not the easiest to get to and replace, I will try and find a link and post it here.

Thanks Ant7 but the motor is fine on a 12v supply - there's just no power getting to it 

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1 hour ago, 209MOR said:

Thanks Ant7 but the motor is fine on a 12v supply - there's just no power getting to it 

To get the best response you need to identify which blower you mean, fresh air one up front, hot air blower in engine compartment, or footwell blowers (3.2s).

Mark

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21 minutes ago, lindsayhbrown said:

My engine blower fan shorted out and melted causing acrid smoke in the cabin, easy replacement but it also took the fan relay out,that cost £250 iirc

Turns out it was the relay - thanks to Ruskiedog who loaned me his one so I could test my set up. Can you recall where you got yours from?

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On 01/10/2022 at 12:33, 209MOR said:

Thanks Ant7 but the motor is fine on a 12v supply - there's just no power getting to it 

No worries, as others have said it depends on which motor you had the issue with, my description was of the one behind the dash for the vents, but as others have said on  the 3.2 you have another of the same motor on the left and right of the footwell. The heater blower motor in the engine bay is of a diffrent type, more often than not it is the relay that causes the issue with this one, anyway- good to hear you got it sorted, I have repaired these relays in the past, so anyone who has a dead one, don't throw it, If I can repair it, I will offer it back to the forum to the next person who needs one.

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10 minutes ago, Ant7 said:

No worries, as others have said it depends on which motor you had the issue with, my description was of the one behind the dash for the vents, but as others have said on  the 3.2 you have another of the same motor on the left and right of the footwell. The heater blower motor in the engine bay is of a diffrent type, more often than not it is the relay that causes the issue with this one, anyway- good to hear you got it sorted, I have repaired these relays in the past, so anyone who has a dead one, don't throw it, If I can repair it, I will offer it back to the forum to the next person who needs one.

It is the blower motor in the engine which is not working, due to a failure in the relay.  I haven't sorted it - just identified the problem. so if you have a solution to repair the relay - i.e. you know which part has failed, I'd be interested to hear.....

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19 minutes ago, 209MOR said:

It is the blower motor in the engine which is not working, due to a failure in the relay.  I haven't sorted it - just identified the problem. so if you have a solution to repair the relay - i.e. you know which part has failed, I'd be interested to hear.....

I did a write up on Pelican years ago on the issues I found with my own,[I will see if I can find it] but safe to say; if you are confident in taking a look yourself, the main thing to look for when you get the can off is broken solder joints, especialy around the heavier parts on the circuit board.

Edited by Ant7
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Going back through my notes on the relay, the issue with mine was both internal relays had open circuit coils, this was also the case with my original DME relay [obviously a power surge in the past posibly from someone jump starting the car]  someone had bridged over the fusebox connections so the fuel pump would run as soon as you put the ignition on, safe to say I put everything back to standard once I fitted a working DME relay! Anyway hope this helps.

 

Edited by Ant7
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