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#1
08-03-2004, 03:30 PM
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1990 300sl no power when a/c is on
my car takes a good two to three seconds of holding down the gas pedal, before it starts to move if the ac is on, without the ac it takes about half to one second before it moves. is this common, or is something wrong. The car has been in the shop getting oil leak fixed for a couple months and i dont know if they messed something up. thanks.
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#2
08-04-2004, 12:05 PM
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That is not normal. The car should immediatly start to accelerate once you release the brake and push the throttle. Is the engine revving and you are not getting grip to the road? Or is it hesitation? Where you press the gas and nothing happens under the hood for awhile? How many miles on the car?
Brian
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#3
08-04-2004, 03:50 PM
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it is a hesitation, where nothing happens for two seconds, there are 86k miles on it.
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#4
08-04-2004, 04:37 PM
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so the engine doesn't immediately speed up (increase RPM) when you press the accelerator? With the car in Park, if you press the accelerator does the engine speed up normally? Or is there a delay between when you press on the gas and the engine responds?
__________________
1999 SL500
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#5
08-04-2004, 04:46 PM
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there is a momentary delay maybe a 1/10 of a second, but nothing major, it has the same delay with air on or off in park. I did notice the rpms seem to be low with the air on, around 6k, where its 7 or 8 with it off.
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#6
08-04-2004, 04:49 PM
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I suspect that the mechanic messed something up when he had the timing chain apart, but i have been told that this car starts out in second gear and that accounts for some delay.
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#7
08-04-2004, 05:04 PM
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My car starts out in second gear too, but there is no delay. That is normal. It sounds like it could be a timing problem though, but the fact that it does it worse when the ac is on, that throws me off. The increased drag on the engine should not have anything to do with hesitation, and the idle control valve should compensate for the increased drag by increasing the idle when the AC is on. I don't know if that model SL has an ICV, but it is worth checking out. Those engines are bulletproof and will run forever, I am sorry that you have had these experiences with your car. I got mine about a year ago, it is a 96 SL320, and I have replaced almost every seal and gasket in the engine (myself). I would think that after having these repairs made that something was not put back like it was. In other words a vacuum line was hooked up wrong, a wire got snapped, one of those plastic vacuum lines could have cracked, who knows. It will take some time to figure out. I can't imagine how frustrating it would be to step on the gas and to have your car think about it first, that is really strange. Tell your mechanic about the hesitation issue and the fact that your idle is dropping with the ac on. Good luck!
Happy Benzing! Brian
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#8
08-04-2004, 05:09 PM
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the mechanic is the one telling me this is normal, however i have not told him about the idle yet. It is interesting that you said a hose could be broken or something because my cruise control doesnt work and i suspect a hose. Thank you for the suggestions.
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#9
08-04-2004, 05:15 PM
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That is interesting, because the idle control valve on my car also handles the cruise control. If you have an ICV, this is what is malfuntioning or not connected properly, and if the idle is not being controlled and "ready" when you step on the gas then this could cause the delay. The computer sets the idle constantly, it depends on a lot of variances, the ac, the climate, the airflow, the transmission position, etc.. Good luck!
Brian
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#10
08-04-2004, 05:20 PM
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thank you, I will have that checked out on monday.
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#11
08-05-2004, 01:35 PM
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You can manually force a 300SL and other models to start in 1st gear. With the car at rest, if you move the shift lever to "2" the transmission will shift from 2nd gear to 1st, and you can return the shift lever to "D" or any of the other forward positions and it will remain in 1st. Might be interesting to see what impact a 1st-gear starthas on the problem.
The 1990 has an idle speed control valve. Your RPMs are low with the A/C on, but if your car idles at higher RPM when cold, I would guess the valve is working. Maybe the compressor is binding internally...If you reach down and turn the clutch on the front of the compressor with your hand it should move with little effort (engine off, of course). Regarding the cruise control, unfortunately, you probably need a new control module. If you have a voltmeter you can check the inputs and outputs to the controller to identify the problem. If you want to do this yourself, I suggest starting a new thread on the topic. I can give you some basics and others who know more than me can contribute.
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#12
08-05-2004, 03:53 PM
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I was unaware of being able to start in first gear, I will try that. I do have a volt meter, and as soon as I am able to find some time, I will also try to test the cruise. I am sure it wont be easy since the cruise doesnt engage unless the car is moving. Thank you for the help.
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#13
08-12-2004, 09:03 PM
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All of the above advice is good. I would just add that my 300SL is noticeably "pokey" with the A/C compressor running. It is normal. The engine just doesn't have enough torque at low / idle RPM's. Starting in 1st gear will help, but it's a PITA in street stop and go driving. You guys with 500's and 600's have probably never even noticed. Mercedes should have engineered this car to start moving in 1st gear with the A/C on.
__________________
Resistance is Futile.
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#14
08-14-2004, 04:11 PM
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The car is now in the shop, and the mechanic found several spark plug wires with cracks in them, i will let you know if anything works.
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