1995 SL500 strange idle and rocking today

[tmwsccsh]

Morning all.

Drove her last night - no problems at all.

This morning, started her up and the idle was a bit higher than usual, around 1000 but then dropped to 500, but was bouncing up and down to around 800 and back, sounding like it was thinking of cutting out and the car was rocking as well. Gave some gas and about 1500 all was Ok, let it go and it started bouncing and rocking again.

Switched off, left it a short while and tried again - same thing.

At this point, I got in the Jag and drove to work.

Any obvious things to check for at the start?

Thanks in advance.

Regards

Tim Watts

 

[EDZ649]

Check the rotor arms and distributor caps first, they suffer with moisture contamination.

Did you leave it parked outside over night? Warm days and cool nights will cause condensation to form.

 

[tmwsccsh]

Cheers - will take a look tomorrow.

She's always out overnight unfortunately. :-(

TMW

 

[Vlad]

Or you have an air leak....check that the pipe under the air cleaner is on firmly.

 

[tmwsccsh]

Or you have an air leak....check that the pipe under the air cleaner is on firmly.

Cheers.

Where's that?

TMW

 

[Doodle]

Underside of the airbox, it sits directly on top of the throttle body.

 

[rorf]

Would help to know what year model your SL500 is

 

[Sp!ke]

Would help to know what year model your SL500 is

First post says it is a 1995

 

[tmwsccsh]

All sorted - HT Leads and Rotor Arms - again!

Only had them replaced in October / November for new ones and they needed doing again - less than 1,500 miles on.

Fortunately, covered by a 1-year warranty on the parts so no real cost.

Should they go that quickly? I would have thought most definitely not...

TMW

 

[donubenz]

My S class V8 had similar problems. The garage said it was because I did not get the engine fully hot with only short trips to work. Apparently they reasoned that there is some moisture in the oil that is not driven off by short trips. Then the distributor being the coldest bit of the motor when it cools attracts the condensation in the cap and corrodes the contacts. Sounded like a good theory to me?
Don

 

[Vlad]

I'm not surprised at the rotors needing to be changed, although I would have thought a quick clean with emery cloth would have cured that, but I'm surprised that the leads needed replacing...what make were they?

As has been stated.....short trips or infrequent use can cause condensation to build up in the caps.

 

[tmwsccsh]

As has been stated.....short trips or infrequent use can cause condensation to build up in the caps.

I shall watch that - have done a few short trips thinking I was doing her good in keeping it running - clearly that's not the case and I shall have to extend my short trips a bit!

TMW

 

[tmwsccsh]

All sorted - HT Leads and Rotor Arms - again!

Only had them replaced in October / November for new ones and they needed doing again - less than 1,500 miles on.

Unbelievable - 6 months on and it looks like they've gone again...

What am I doing wrong?

The car is not used too often (once every week or so) but I make sure the first run is around 5 miles or so so it's not a short a run being done.

I don't get how it's so sudden though - there's no indication on the previous journey and then it happens - the clue is the (very) rough idling after about 5 minutes of running - and I am letting her "warm up" before driving off.

She's back with my mechanic chap over Christmas (got family staying so need the bigger car!) and I will get her back in the new year. He's already said that if it is indeed the HT Leads again the supplier will be questioned as to what's going on, but this is getting annoying now...

Anyone got any other pointers as to how this could be going after just 6 months?

Thanks in advance.

TMW

 

[Dieselman]

It is moisture in the distributor. Ensure the engine gets properly hot quickly and the seal inside the distributor cap is good.

If it continues, drilling a hole in the cap to allow moisture out may be a solution. You don't need to keep replacing the cap, just dry it out.

 

[tmwsccsh]

It is moisture in the distributor. Ensure the engine gets properly hot quickly and the seal inside the distributor cap is good.

If it continues, drilling a hole in the cap to allow moisture out may be a solution. You don't need to keep replacing the cap, just dry it out.

Thanks for this.

Have forwarded the info on to my mechanic chap for his thoughts.

Here's hoping it is as simple as this...

TMW

 

[IanA2]

The car is not used too often (once every week or so) but I make sure the first run is around 5 miles or so so it's not a short a run being done.
TMW

I not quite sure that I understand what you are saying here by the first run. Are you saying that you give it two runs? The reason I ask is that I'm not sure that I'd really call 5 miles a long run for that engine. Only just warmed up really.

 

[ivan1983]

My guide for when the oil is starting to get warm is when the oil pressure gauge drops from 3 at idle, this can take quite some time!

 

[tmwsccsh]

I not quite sure that I understand what you are saying here by the first run. Are you saying that you give it two runs? The reason I ask is that I'm not sure that I'd really call 5 miles a long run for that engine. Only just warmed up really.

Typically, it's once a week trip out is to work and back. So, 5 miles or so to the office, then 5 miles or so back in the evening.

I've heard about "not long runs for these engines" before and similar, but surely there are times that everyone just pops down the road to the local shops or something and therefore only does a mile or 2 on a trip? We can't all spend our whole lives doing 10 mile trips minimum just because it's what the engine expects, surely? And I will call you all surely!

Used to have a 5 Litre V8 Mustang and that was my daily runner - all lengths of journeys and it never missed a beat or had any similar problems to this in the 4 years I had it...

TMW

 

[IanA2]

Typically, it's once a week trip out is to work and back. So, 5 miles or so to the office, then 5 miles or so back in the evening.

I've heard about "not long runs for these engines" before and similar, but surely there are times that everyone just pops down the road to the local shops or something and therefore only does a mile or 2 on a trip? We can't all spend our whole lives doing 10 mile trips minimum just because it's what the engine expects, surely? And I will call you all surely!

Used to have a 5 Litre V8 Mustang and that was my daily runner - all lengths of journeys and it never missed a beat or had any similar problems to this in the 4 years I had it...

TMW

Well, I wouldn't start my SL unless I was going ten miles plus. I would use another car. I don't know what others think, but I think a two five mile trips once a week are the cause of your problems with the car. Just my opinion.

 

[jonthetourist]

Typically, it's once a week trip out is to work and back. So, 5 miles or so to the office, then 5 miles or so back in the evening.

I've heard about "not long runs for these engines" before and similar, but surely there are times that everyone just pops down the road to the local shops or something and therefore only does a mile or 2 on a trip? We can't all spend our whole lives doing 10 mile trips minimum just because it's what the engine expects, surely? And I will call you all surely!


TMW

We all do short runs, but I think the point being made is that your regular run is not adequate to warm up the engine and disperse moisture in your distributor cap. But it depends. My regular run is 6.5 miles without any traffic lights, but I come back after 2 hours so the engine has not fully cooled down before I set off back. If you drive in heavy traffic it is feasible that some of your 5 miles is spent with the engine warm.

Jon (fellow sufferer)