Hey everyone, so I had posted another issue I was having with some valve train noise and as that post was being responded to my car started to do this strange misfire stumble at idle. I had just replaced all of the ignition coil packs with new and I'm not getting any codes for a misfire. The car feels slightly less responsive where it once felt crisp also, I can duplicate the stumble if I simply just gently step on the gas pedal and let off and as the RPMs drop down the car will do a little hiccup and the hiccup feeling is constant at idle especially when it's cold. I had replaced all the plugs and coil packs as previously mentioned and I've gotten no codes except for an O2 sensor which I replaced and when i plugged in on the scanner it shows that it's functioning properly. Has anybody else dealt with this issue?

 

Oddly enough, I have a very similar issue that i can't figure out. Pressing the gas pedal very lightly, maybe quarter throttle off of a dead stop and holding that position, i get a hiccup/stall/stumble, and it picks right back up and is fine. It's been going on almost as long as I've owned the car and i can't track it down. I also have what seems like a slight misfire at idle, however its not exactly a misfire as its not misfiring. Its a random, very slight rough idle that smooths out and comes right back. The only thing i can think of is a VAC leak somewhere. I was also getting a code (No Check engine light) for "Unmetered air" which leads me to believe its a Vac leak, or something in the Intake system is not completely sealed (Which is likely considering i'm running an aftermarket intake)

My only suggestion is to hook it up to a really good scanner, like an AUTEL that will read every single code and module and see what comes back. Just because its not throwing a check engine light doesn't mean it won't tell you that something else is going on causing the issue. For example, My "Unmetered air" issue, is being resolved by the computer automatically adjusting AFR, and it only happens for a split second.

The last suggestion i could give to completely rule out a Vac leak anywhere in the system is to go out and buy an automotive smoke machine. That will give you your answer and you can cross it off the white board.

- Joe

 

Yeah man, I wish I had access to a really good scanner. I'm almost positive it's a misfire somewhere between the new coils I put in or maybe one of the original spark plug wires which were never changed and the cars got 200,000 mi on it. I didn't see anything obvious, but you know how ignition wires are next week. I'm swapping out the ignition wires of an sl55 that my friend owns and I'm going to try swapping in the wires from his car which are good. Right now we're just doing it as preventative maintenance and see if that solves the issue, but just in case it doesn't, I'm still open to input from anybody who's had the same exact issue

 

In my S55, I was chasing a weird idle issue. It would be fairly smooth while in gear, but the idle would race up to about 1,500rpm in neutral and be fairly rough. It would surge and drop a couple hundred RPM, but no codes. It would also jump a bit when I put it in gear, due to the higher RPM, so I had to be careful. It ran a bit rough at slower speeds, but very drivable. Scanner showed an issue with the accelerator sensor/wiring. The sensor is integral with the pedal assembly, so I ordered a new pedal/sensor. It is a really easy swap that took maybe 7 minutes. Problem solved! It idles perfectly smooth right where it should be. Pedal is a couple hundred $ and really one of the easiest DIY jobs on these cars. It is one single 10mm bolt and one wire harness. Worth exploring with the symptoms you are describing.

 

Thanks for the input sadly this is not that kinda issue it feels like a straight up misfire ! I'm going to remove the supercharger belt today and see if that changes anything maybe a pulley is bad placing a strain on the engine if that's possible idk just know I need to resolve it asap

 

ok so ran a smooth idle test and noticed cylinder 4 is bouncing into the 5.xx range . im wondering if either that plug is defective or possibly the injector ring is leaking or defective injector all together ?

 

Why not just start with all plugs and coil packs first? They're probably due. These plugs are spec'd at 5/50 which I've always done but never "felt" needed to be done. Meaning they're done before you notice ill effects.

The other thing I'm knocking up against is all of the O-Rings and rubber at the back of the supercharger are probably due by now as well. We were chasing a CEL on mine which turned out to be a fuse related to the SAI pump. But along the way, spraying brake cleaner at the rear driver side of the intake we noticed her stumble a bit, which meant what we were spraying was getting where it shouldn't. So next oil change every rubber gasket and O-ring at the rear of the intake is getting changed. 20years living at the back of this hot engine sandwiched against the firewall on long 20+ hour freeway runs, yeah they're done.

CEL is gone and no stumble, but that just means any air leakage is within spec where the ECU can adjust the A:F ratio. That doesn't mean the rubber shouldn't be replaced. And I'm still seeing 21mph on highway runs over 80mph.

Point is, these aren't "break fix" cars. If you're seeing ill effects, you're already late. Download the maintenance schedule, catch up and stay caught up. Otherwise you're chasing ghosts.

maw

 

Could plugs wires all new and good

 

Meant to type - coils , plugs , wires are all new and good

 

This + my prior response + your other thread about a hiss all point to a vacuum leak in my mind. Have you had the car smoke tested?

maw

 

I just had a smoke machine dropped off by a friend. I'm going to look at the procedure on the best way to do it for this car and smoke it tonight or tomorrow afternoon. I'm also going to pull the belts and check the pulleys. The car still has that misfire feeling but it's not misfiring. As for the strange sound totally it's a vacuum leak or I was thinking possiblity it's a bad pulley. I do have a whine coming from a pulley at idle that's independent of the rpm and subside along with that strange chatter sound from the rear cylinder on the driver's side somewhere between the valve area on the surge tank and that intake roller rocker. The maintenance on this car prior to me acquiring it was seriously neglected so I've been playing a game of catch up. I hit a bad pothole on Thursday bent my rim popped two tires got the rim fixed but now the car has a nasty vibration at 65 so I'm assuming it's out of balance needless to say, the money that went to rectifying the tires and the rim repair would have been earmarked for the engine repair instead. I'm going to remove the belts this weekend. After I smoke, test it and see what I can isolate. Car has $200 and 5,000 mi on it. And as I mentioned when I did the valve cover gaskets that one metal vacuum line that goes into the rear driver side of the supercharger had fallen out of place and the rubber grommet dislodged. I was able to find the rubber grommet laying on top of the intake manifold and put it back in and put the metal line back into where it belongs. But I wonder if that's the place where I'm leaking since that grommet is obviously not tight anymore I appreciate all your feedback and will be looking at some of the things you mentioned in this listing this weekend when I finally get back into it now that I have the smoke machine I wish I had somebody local to me in the Hudson valley New York area that had the star program to scan the car. That would be really helpful either way. Thank you for your feedback. It's not wasted

 

Find the vacuum leak OP?

 

That loose intake hose would cause too much air to fuel and throw a CEL ("maybe" ... I don't remember), but once you plug it back in all is well. There is nothing to "secure" it in place -- that fitment is normal. Smoke test the car and change the idler pulley -- I'm sure that's the one that's complaining. They go every few years, nothing abnormal about it. I do mine every 5/50 with plugs and transmission fluid.

That metallic sound near the rear of Bank 1 is what's concerning me, but I'd like to see a smoke test done first. If there's some hose missing, that would let you hear engine internals when you shouldn't.

Keep us posted.

maw

 

I'm going to smoke the car today since it's my first day off in a week . It's strange the check engine light isn't on yet the Mercedes malfunction indicates there is 1 & sometimes 2 malfunctions . I scan the car with my budget scanner and get nothing other then a code for an airbag sensor passenger side . I scanned the car with another Bluetooth scanner from a friend and get the following . These codes do not come up in the engine section of the scanner but some other sub section .
P202a-001- fuel pump relay positive short
P202a-002- fuel pump relay short to ground
P202a-008- fuel pump relay operational problem
b1416- coolant circulation pump short or positive overload
B1634- hcs pump short to ground
Attached are pictures of the scan session . My buddy says the scanner some times provides junk codes but this is what I got from the other scan session despite no actual check engine light which I know works because it came on when I missed that vacuum line falling out of the back of the supercharger and started the car up and ran it. If these are accurate, they seem like pretty significant codes and the check engine light should come on yet it's not coming on. When I search the p202 codes on the forum they point to idle speed control 🙄 that thread focused on a guy grinding his TB shaft and having to replace TB with stock unit

 

Okay, that crazy sound that I hear that. It sounds like a chain chattering is the blade in my throttle body the flap is what's chattering. Does this mean it's time for a new throttle body?
I examined it further and can feel the butterfly flap is loose despite the 2 screws in the shaft being tight . Do I simply look to replace the butterfly plates ? Is there an easy free fix for this or am I DOA and have to replace the entire unit 🤔

 

If there is shaft wear in the throttle body or the electric motor is making chattering you may get to replace the throttle body.

 

The chatter is the butterfly flap. It's got free play in it but the screws are tight. Also I smoke tested the car and didn't get any smoke out of anywhere concerning in any heavy amount. I'm going to order surge tank gaskets a throttle body gasket and since I can't find that grommet for that vacuum line I guess silicone's going to be my friend. I know I'm not going to pay. Mercedes $68 for that little tiny rubber grommet for the Evap line into the rear of the super charger that's insane if that's the actual price . I was thinking about taking the throttle body off to clean it but I don't have gaskets on hand to replace the ones currently installed I don't believe the codes that were listed by the scanner are accurate and thoughts ?.

 

If you have ANY smoke, the gaskets and O-Rings need replacement. Those are the ones I was talking about living 20 years at the back of a hot engine bay.

And you probably need a new throttle body as well. Not surprising, especially if the car was once tuned, as most of them have been at this point.

Guessing from a long way away, you might have bought one that was tuned, ridden hard, put up wet, then "put back stock" for sale.

I'd clear those codes, get the car on a battery tender to full charge, then re-scan and see what comes back. But if throttle body and some misc gaskets and O-Rings are all the car needs, consider yourself lucky. Buy a used TB off ebay, new OE gaskets and O-Rings and have a nice day.

Welcome to the game.

maw

PS... for what I've prescribed above, I wouldn't even bother to DIY it. A qualified indy will have that done in a few hours for way less grey matter than you're ever going to spend on it. Also if I was going to do that, I'd do the EGR valves too. If I can find an ebay link I'll come back and post it. Here you go... these... https://www.ebay.com/itm/11663188445...IAAOSwi-tjfQkX ... and this... https://www.ebay.com/itm/11654596473...0AAOSwx35n7k7M ... so for $500 in parts and a few hours of work by someone who knows what they're doing your problems could all be solved... if you never drive the car as it was engineered, why bother??

 

I definitely agree with you. The throttle body needs replacing I can't find any type of fix for that issue I'm having with the free play in the throttle body butterfly flap also To my knowledge this car doesn't have an EGR valve. It's supercharged and I was told there is no EGR on this model. Otherwise I would have replaced it right off the bat I build custom motorcycles for a living and would much rather put the $500 in labor towards additional parts for the car than to pay somebody else to do it. Doing the work isn't the problem. Plus I have all the tools. It's knowing what else to do while I'm doing the throttle body. So the plan right now is to hit the map sensor because it'll be accessible. I already have all new hoses for the breathers I figure gaskets for the throttle body and surge tanks what are the o-rings and seals? Should I focus on replacing considering I've already redone the valve cover gaskets and resealed? The breathers and I greatly appreciate your detailed response.

 

The things I called EGR valves you definitely have. I just did mine. Based upon what my mechanic (and friend) told me, half the S55 chasing CEL right now are because of those. TLDR, I don't have that kind of patience.

Fine, do the work yourself. Just buy all the OE seals, gaskets and o-rings where you see smoke. Yes I said and mean all.

That with the throttle body might just get you where you need to be. Fuel filter is table stakes for these by now (I'm on my 4th... change them damned near like cabin filters).

Start there, report back. For your skill set, this is all simple. When you reconnect the battery all systems might be go.

maw

 

Can you please elaborate on what exactly you're referring to as an EGR valve?

 

Look at the eBay links.

maw

 

I'm exploring deleting the entire system but being in NY/NJ my assumption is that it would most likely result in an issue with emissions inspection unless I sprung for a custom tune .
I might just pull and clean . I've not gotten any codes pointing towards the system having an issue but understand the build up will cause issues . My throttle body is in the mail so I plan to replace the map sensor , breather hose Union and surge tank gaskets along with any gaskets related to the TB . I'm trying to locate that rubber grommet for the metal Evap vacuum line that runs into the back of the supercharger. And if i can't find it or a viable option as a replacement it's going to get sealed into place with silicone along with the metal line .

 

For $100 bucks why bother cleaning them. My guy said he could dip them in some acid, yada yada. I looked at him like he was silly. "Habibi, for $100 bucks just toss in new ones and don't worry about it. If they're no good, then we'll acid dip all 4 and I'll have 2 spares." No need to make work. This isn't a science project. I don't think the engine will work well without them but that's over my head. I'm not a mechanic. I just want the car to run right with minimum headache.

maw

PS... as tempting as it might me, for whatever reason I don't know, these cars don't need a lot of re-engineering. Find the offending part, replace it with a new (or used if unavailable) factory part and move on, is almost always the best course of action. Anything else tends to be asking for varying amounts of trouble for almost no benefit, I've observed over the years. That's why they're Mercedes Benzes. No need to recreate that wheel and no benefit from doing so as a general matter.

 

It's not $100 for new ones it's $250 for 2 new ones . Used ones are $110 and who knows their age of mileage or how long they will last but I hear you