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Old 11-06-2003, 10:45 AM
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Join Date: Jul 2003
Posts: 42
Hesitation Problem Solved (hopefully)

Idle Hesitation Problem Solved (I Hope)

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 hesitation would appear. On somedays, this would not occur at all. Cold Idle was always a little rough.

Car recently received 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 called saying the car was fixed. 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 various parts of the 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.

It seems like the problem has been solved. Car runs very smoothly. 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 here is the 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.


Mike G
1991 500 SL
2002 BMW 745i
2003 Harley Electra Glide
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Old 11-06-2003, 11:51 AM
haasman's Avatar
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Join Date: Jun 2001
Location: San Francisco, CA
Posts: 3,097

Glad to hear you have solved your problem .... did you see this: Hesitation

'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)
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Old 11-07-2003, 11:26 AM
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Join Date: Jul 2003
Posts: 42
I saw it, but I do not think it applied to me. I went through several tankfuls of gas.

Now that I think of it, I should never have let the first shop clean the injectors. Perhaps the removal and refitting of them damaged them in some respect. It was only a couple weeks later that the problem started.

With injectors on my car costing around $20.00 a piece, its simply not worth fooling around trying to diagnose a hesitation or rough idle issue. In fact, at that price, I think they should be a maintenance item at the 120K mile mark.

1991 500 SL
2002 BMW 745i
2003 Harley Electra Glide
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