Idle Hesitation Problem Solved (I Hope)

[Mike G]

I have a 1991 500SL with 115kmiles.

I posted a couple weeks ago about an intermittent hestiation as the car moved away from a stop. It seemed to come on all at once as you were driving. Car would actually temporarily lose power -- and then hestition would appear. Somedays, this would not occur at all. Cold Idle was always rough though.

Car had recently has a complete tune (rotors, caps, plugs, lamda, filters etc.) They also "cleaned" injectors on a machine. A month after the tune is when the problems started.

I read over a hundred posts on idle hesitation. There are dozens of reasons why my car could be doing this -- OVP, wiring harness, etc. I did not know where to start.

I decided to skip my independent mechanic and take it straight to the dealer. I figured that they worked on more of these and the last thing I wanted was a guy guessing at what it was. It would be cheaper to pay more but get it done right the first time.

Well, went to the dealer (Fletcher Jones (formerly Loeber) in Chicago) and they made the Lambda sensor adjustment and adjusted the overall fuel/air mixture (tower). They said car runs great. However, when I picked it up, it was the same. $400.00 down the drain.

The Dealer was very sympathetic and told me to bring it right back. They could not figure it out until they had their best guy look at it. They ran various ignition tests and they said they even jumped some wires to test ignition, but hesitation was still there. They finally concluded that it was the injectors.

Now this is something I could have done myself, but figured let them do it. I wanted this problem solved, and they were on its trail.

Problem has been solved. Car runs amazingly. Now this was an intermittent problem, so I am praying that it will not return, but car idles better and I can see a real difference.

So there is my story. Moral of the story -- if a car has over 100K miles, replace the injectors before you spend any additional money. Do not have them cleaned. A half a dozen bottles of Techron did me no good. I think it was an electrical problem in the injector(s).

Thanks

Mike G

1991 500 SL
115,000 miles.

[LeaUK]

Mike

Very interesting. I once owned a 190E 2.6 which I loved and cared for, but the only thing that I couldn't cure was the rough idle. Finally I upgraded to my new baby and sold the 190 to a buddy who also now loves her and cares for her too...

but more importantly, he's in the trade and has changed everything apart from the injectors. A quick call to MB and they confirmed that the injector on that model only has a life expectancy of 70K miles. Uhm, perhaps this is common for injectors in general?

Also bear in mind that injectors have micro-filters buried within so fuel contamination could reduce life even further.

Glad it's all sorted now - but guess 8 wen't cheap though!!

[Mike G]

Learoy,

Injectors are a little more than $20 each on the internet. For this price, they should be a maintenance item at the 100k mark.

I really wish the first mechanic had just changed them.

MG