Sudden Idle problems...and panic. - PeachParts Mercedes-Benz Forum

jkazzoun · #1 04-30-2002, 09:49 AM

Yesteday evening I pulled up to a stop light and suddenly felt an irregular, fairly hard shudder at idle. This morning it was there as well. The bad idle seems a little more pronounced this morning.
It seems fine at all speeds but idle. If I shift to Neutral at rest, the RPM's climb slightly and things are better. It may stumble when I pull off, but that could be my imagination as well. It also could be the engine is rougher at speed, but I really don't think so..

I purchased the car 3 weeks ago. 10 days ago I had the dist. cap., rotor, fuel filter, oil/oil filter, transmission fluid/filter and plugs all changed just becuase (not becuase of any poor performance). It has been perfectly fine until last night.

The panic? First thing I thought of was the timing chain. Why? Because my car has 110,000 and I know I need to get it done as a maintenance item. And, that would be the worst case scenario.

Seriously though, could it just be a bad (or loose) plug wire that affects it only when the RPM's are low and spark weaker?

Please help! The good MB garage near here is backed-up and I don't trust anyone else!

Thanks in advance,

Joe

MikeTangas · #2 04-30-2002, 10:44 AM

Are any idiot lights illuminated when the poor idle manifests itself, perhaps the ABS light? Check the fuse on the OVP, it may be bad or even the OVP may be going south./

jkazzoun · #3 04-30-2002, 10:59 AM

Nope, no idiot lights. OVP?

Austin814 · #4 04-30-2002, 01:15 PM

OVP (Over Voltage Protection) There should be a unit with a fuse in it...depending on your model where it is located. The OVP causes hard starting, rough idle etc. I had the problem once with my 190E hard starting and the OVP was the problem. Another thing to consider would be check the brushes on the alternator, if they are getting bad the output might be falling under 10 volts at idle which might be causing a bad spark. Do a search for "OVP" on this forum and I'm sure you find lots of info in the OVP.

-Brad

jkazzoun · #5 04-30-2002, 01:35 PM

Brad,

Thanks. I've done OVP searches and could not find the definition (was still looking when you posted).

I get radio interference coming on and off when I go over bumps. Truthfully, I can't tell if it is one speaker or both. If it is one, then it is a stereo issue, if both I was thinking maybe a bad plug wire. However, to your thought on the alterantor, a mechanic told me the radio noise (which was occuring when he changed some parts for me) was possibly the alternator. hmm...

Mike, if the SRS light not on does that rule out the OVP or not?

Thanks,

Joe

jkazzoun · #6 04-30-2002, 01:48 PM

one more thing, it starts just fine...

jkazzoun · #7 04-30-2002, 02:11 PM

last addition...it idles for 3-6 seconds just perfectly and then the shudder hits..boom..then goes...it is not like the steady rough idle or stumbling I've experienced in the past..just a brief, failry harsh shake...at first I thought a heavy truck was hitting the over pass seams behind me.

just trying to be descriptive...

Austin814 · #8 04-30-2002, 02:57 PM

The OVP is very simple to check, it’s a little silver box next to your firewall. There will be a 10 Amp fuse in it. If it is blown then replace it, if not...rule it out. I don’t know where it is on your model but on my 190E if I recall correctly it was in the back of the front driver’s side fuse box. There was a flip up cover over the fuse and the fuse pulled out horizontally. I'd have to look again to be completely sure as it was almost 2 years ago but again, it’s very simple to check.

carman850 · #9 04-30-2002, 03:01 PM

Have you tried some fuel system cleaner? maybe just as sample as that.

Before I had the same sudden shudders plus rough idle when cold, they all went away after I used one bottle of fuel system cleaner. My car is a 92 400E, I spent $1000 for parts with no luck, finally $10 cleaner solved the problem.

Jerry Hudson · #10 04-30-2002, 03:19 PM

The OVP on a 88 560 SL in behind the kick panal to the right of the pasenger side foot well.

jkazzoun · #11 04-30-2002, 04:35 PM

Thanks all.

I will check the fuse after work tonight and if it is not blown, I'll buy the fuel system cleaner. Cant eh OVP be bad but the fuse still be good?

Sitting at my desk, I lean towards the OVP and/or associated fuse being the likey cause just because it came on so suddenly. The idle has been smooth as glass until just last night (and is smooth as glass between the intermitent shudders).

Will report back...

MikeTangas · #12 04-30-2002, 07:33 PM

The OVP may trigger the ABS light not the SRS. SRS will trigger if a fault in the SRS system or voltage drops below 10v. If an intermittent alternator problem, SRS light should go out once the system is above 10.1v.

jkazzoun · #13 05-01-2002, 09:20 AM

Mike, I meant ABS, sorry...

jkazzoun · #14 05-01-2002, 05:42 PM

Okay, so last night I put in some fuel system cleaner and got in the car. It was running worse than before...The intermitent boom turned into a more generally rough idle. I tried to locate the OVP. I see several small silver squares above the fusebox on the passenger kickpanel, but don't know which one it is. Any help?

Today I took it over to the local independant (Roxbury Foreign Car Repair in Northern NJ) to have look at the fuse. In the way there the problem worsened and the engine was rough accelerating up to about 2500 rpm.

I got there, the whole problem went away, we did not look at the OVP fuse and I drove off (I did however schedule to have the timing chain replaced as a maintenenace item).
He said maybe a fuel injector is sticking or there is some other fuel management issue. He basically said it could be a hundred things...

Two miles later the problem resurfaced and now the car just idels rough, but at the right speed. The engine remains rough up to about 2000 RPM, but still puills fine without any hesitation. I don't think it's misfiring. It starts up just fine.

Anyway, neither he nor the dealer can look at it for a couple of weeks so I'[ll just drive it until I take it in for the timing cahin on 5/21 - unless I break down or it gets much worse. I'm not really a do it yourselfer excpet for minor, minor, minor things (and interior, trim stuff).

Any thoughts/ideas would be great, otherwise I'll report back later.

Jerry Hudson · #15 05-01-2002, 06:22 PM

you are in the right area for the OVP. it is the silver box with a red plastic cap on it that covers the fuse. hope this helps.